试图调用虚拟方法无效android.widget.ListView.setAdapter [英] Attempt to invoke virtual method 'void android.widget.ListView.setAdapter

问题描述

我试图让包含这是与选项卡的viewpager片段中的图片和文字列表视图，这样我就可以向左或向右滑动以打开另一个片段。

我是比较新到Android所以我可能会做可能是完全错误的。我可以建立项目完全正常，但那么当模拟器运行它崩溃（LOG在页面底部显示的）。

我创建了一个单独的应用程序，并成功能够创建一个列表视图，但是当我尝试它，就像这样的片段中结合，这是行不通的。
这是我下面code

  

MainActivity.java

 进口的java.util.ArrayList;
进口的java.util.List;
进口java.util.Locale中;进口android.app.ListFragment;
进口android.content.Intent;
进口android.support.v7.app.ActionBarActivity;
进口android.support.v7.app.ActionBar;
进口android.support.v4.app.Fragment;
进口android.support.v4.app.FragmentManager;
进口android.support.v4.app.FragmentTransaction;
进口android.support.v4.app.FragmentPagerAdapter;
进口android.os.Bundle;
进口android.support.v4.view.ViewPager;
进口android.view.Gravity;
进口android.view.LayoutInflater;
进口android.view.Menu;
进口android.view.MenuItem;
进口android.view.View;
进口android.view.ViewGroup;
进口android.widget.AdapterView;
进口android.widget.ArrayAdapter;
进口android.widget.ImageView;
进口android.widget.ListView;
进口android.widget.TextView;
进口android.widget.Toast;
公共类MainActivity扩展ActionBarActivity实现ActionBar.TabListener {    / **
     *本{@link android.support.v4.view.PagerAdapter}，将提供
     *对于每个部分的片段。我们使用
     * {@link FragmentPagerAdapter}衍生，这将让每一个
     *加载到内存中的片段。如果这成为太内存密集型，它
     *可能是最好切换到
     * {@link android.support.v4.app.FragmentStatePagerAdapter}。
     * /
    SectionsPagerAdapter mSectionsPagerAdapter;    / **
     *本{@link ViewPager}将承载部分内容。
     * /
    ViewPager mViewPager;
   私人列表＆LT;岗位＆GT; myPosts =新的ArrayList＆LT;邮电GT;（）;
    @覆盖
    保护无效的onCreate（捆绑savedInstanceState）{
        super.onCreate（savedInstanceState）;
        的setContentView（R.layout.activity_main）;
        //设置操作栏。
        最后的动作条动作条= getSupportActionBar（）;
        actionBar.setNavigationMode（ActionBar.NAVIGATION_MODE_TABS）;        //创建将返回一个片段为三个的适配器
        //活性的主要部分。
        mSectionsPagerAdapter =新SectionsPagerAdapter（getSupportFragmentManager（））;        //设置的ViewPager与部分适配器。
        mViewPager =（ViewPager）findViewById（R.id.pager）;
        mViewPager.setAdapter（mSectionsPagerAdapter）;        //当不同部分之间滑动，选择对应的
        // 标签。我们也可以使用ActionBar.Tab＃select（）来做到这一点，如果我们有
        //为Tab的参考。
        mViewPager.setOnPageChangeListener（新ViewPager.SimpleOnPageChangeListener（）{
            @覆盖
            公共无效使用onPageSelected（INT位置）{
                actionBar.setSelectedNavigationItem（位置）;
            }
        }）;        //对于每一个应用中的部分，添加标签，操作栏。
        的for（int i = 0; I＆LT; mSectionsPagerAdapter.getCount（）;我++）{
            //创建对应于定义的页面标题文字标签
            //适配器。同时，指定此活动的对象，它实现
            //将TabListener接口，回调（监听程序）进行时
            //这个选项卡中选择。
            actionBar.addTab（
                    actionBar.newTab（）
                            .setText（mSectionsPagerAdapter.getPageTitle（I））
                            .setTabListener（本））;        }         意向意图=新意图（MainActivity.this，NotMainActivity.class）;
        startActivity（意向）;
        完（）;
    }    @覆盖
    公共布尔onCreateOptionsMenu（菜单菜单）{
        //充气菜单;如果是present这增加了项目操作栏。
        。getMenuInflater（）膨胀（R.menu.menu_main，菜单）;
        返回true;
    }    @覆盖
    公共布尔onOptionsItemSelected（菜单项项）{
        //处理动作栏项目点击这里。操作栏会
        //自动处理上点击主页/向上按钮，只要
        //你在AndroidManifest.xml中指定一个父活动。
        INT ID = item.getItemId（）;        // noinspection SimplifiableIfStatement
        如果（ID == R.id.action_settings）{
            返回true;
        }        返回super.onOptionsItemSelected（项目）;
    }    @覆盖
    公共无效onTabSelected（ActionBar.Tab选项卡，FragmentTransaction fragmentTransaction）{
        //当选择给定的标签上，切换到相应的页面
        //的ViewPager。
        mViewPager.setCurrentItem（tab.getPosition（））;
    }    @覆盖
    公共无效onTabUnselected（ActionBar.Tab选项卡，FragmentTransaction fragmentTransaction）{
    }    @覆盖
    公共无效onTabReselected（ActionBar.Tab选项卡，FragmentTransaction fragmentTransaction）{
    }
    / **
     * A {@link FragmentPagerAdapter}返回对应片段
     *章节/标签/页面。
     * /
    公共类SectionsPagerAdapter扩展FragmentPagerAdapter {        公共SectionsPagerAdapter（FragmentManager FM）{
            超（FM）;
        }        @覆盖
        公共片段的getItem（INT位置）{
            //的getItem被称为实例化片段为给定的页面。
            //返回一个PlaceholderFragment（定义如下静态内部类）。
            开关（位置）{
                情况下0：
                    返回新TheWallFragment（）;
                情况1：
                    返回新PeekFragment（）;
                案例2：
                    返回新CameraFragment（）;
                默认：
                    打破;            }            返回PlaceholderFragment.newInstance（位置+ 1）;
        }
        @覆盖
        公众诠释的getCount（）{
            //显示3总页​​数。
            返回3;
        }        @覆盖
        公共CharSequence的getPageTitle（INT位置）{
            区域设置L = Locale.getDefault（）;
            开关（位置）{
                情况下0：
                    返回的getString（R.string.title_section1）.toUpperCase（升）;
                情况1：
                    返回的getString（R.string.title_section2）.toUpperCase（升）;
                案例2：
                    返回的getString（R.string.title_section3）.toUpperCase（升）;
            }
            返回null;
        }
    }    / **
     *包含一个简单视图中的占位符片段。
     * /
    公共静态类PlaceholderFragment扩展片段{
        / **
         *片段参数重新presenting本节号
         *片段。
         * /
        私有静态最后弦乐ARG_SECTION_NUMBER =SECTION_NUMBER;        / **
         *返回该片段的一个新实例为给定的部
         *号。
         * /
        公共静态的newInstance PlaceholderFragment（INT sectionNumber）{
            PlaceholderFragment片段=新PlaceholderFragment（）;
            捆绑ARGS =新包（）;
            args.putInt（ARG_SECTION_NUMBER，sectionNumber）;
            fragment.setArguments（参数）;
            返回片段;
        }        公共PlaceholderFragment（）{
        }        @覆盖
        公共查看onCreateView（LayoutInflater充气器，容器的ViewGroup，
                                 捆绑savedInstanceState）{
            查看rootView = inflater.inflate（R.layout.wall_layout，集装箱，FALSE）;            返回rootView;
        }
    }}
 

  

NotMainActivity.java

 公共类NotMainActivity扩展FragmentActivity {    私人列表＆LT;岗位＆GT; myPosts =新的ArrayList＆LT;邮电GT;（）;    @覆盖
    保护无效的onCreate（捆绑savedInstanceState）{
        super.onCreate（savedInstanceState）;
        的setContentView（R.layout.activity_main）;
        populatePostList（）;
        populateListView（）;       registerClickCallBack（）;
        System.out.print（主要活动开始）;    }
    私人无效populatePostList（）{
        myPosts.add（新帖子（渥太华，安大略省，787，图片我的狗！，R.drawable.dog））;
        myPosts.add（新帖子（渥太华，安大略省，787，图片我的狗！，R.drawable.dog））;
        myPosts.add（新帖子（渥太华，安大略省，787，图片我的狗！，R.drawable.dog））;
        myPosts.add（新帖子（渥太华，安大略省，787，图片我的狗！，R.drawable.dog））;
        myPosts.add（新帖子（渥太华，安大略省，787，图片我的狗！，R.drawable.dog））;
        myPosts.add（新帖子（渥太华，安大略省，787，图片我的狗！，R.drawable.dog））;
        myPosts.add（新帖子（渥太华，安大略省，787，图片我的狗！，R.drawable.dog））;
        myPosts.add（新帖子（渥太华，安大略省，787，图片我的狗！，R.drawable.dog））;    }    私人无效populateListView（）{
        ArrayAdapter＆LT;岗位＆GT;适配器=新MyListAdapter（）;
        ListView控件列表=（ListView控件）findViewById（android.R.id.list）;
        list.setAdapter（适配器）;        }
    //把手上的列表项点击
    私人无效registerClickCallBack（）{
        ListView控件列表=（ListView控件）findViewById（android.R.id.list）;
        list.setOnItemClickListener（新AdapterView.OnItemClickListener（）{
            @覆盖
            公共无效onItemClick（适配器视图＆LT;＆GT;母公司，观景，INT位置，长的id）{
                帖子clickedPost = myPosts.get（位置）;
                字符串消息=你点击+位置
                        +后的定位是+ clickedPost.getPostlocation（）;
                Toast.makeText（NotMainActivity.this，消息，Toast.LENGTH_LONG）.show（）;
            }
        }）;
    }
    私有类MyListAdapter扩展ArrayAdapter＆LT;岗位＆GT; {
        公共MyListAdapter（）{
            超（NotMainActivity.this，R.layout.item_view，myPosts）;
        }
        @覆盖
        公共查看getView（INT位置，查看convertView，父母的ViewGroup）{
            //确保我们有一个观点一起工作{可能给空}
            查看ItemView控件= convertView;
            如果（ItemView控件！= NULL）{
                。ItemView控件= getLayoutInflater（）膨胀（R.layout.item_view，父母，假）;
            }
            //找到邮局的工作。
            帖子currentPost = myPosts.get（位置）;
            //填充视图
            ImageView的ImageView的=（ImageView的）itemView.findViewById（R.id.item_postImage）;
            imageView.setImageResource（currentPost.getIconID（））;            //在标题填写            TextView的titleText =（TextView中）itemView.findViewById（R.id.item_postText）;
            titleText.setText（currentPost.getPosttitle（））;            //设置票数
            TextView的voteText =（TextView中）itemView.findViewById（R.id.item_postVoteText）;
            voteText.setText（currentPost.getPostvote（））;            返回ItemView控件;
        }    }}
 

  

Posts.java

 公共类职位{
    私人字符串postlocation;
    私人字符串postvote;
    私人字符串posttitle;
    私人诠释iconID;    公共帖子（字符串postlocation，字符串postvote，字符串posttitle，诠释iconID）{
        this.postlocation = postlocation;
        this.postvote = postvote;
        this.posttitle = posttitle;
        this.iconID = iconID;
    }    公共字符串getPostlocation（）{
        返回postlocation;
    }    公共字符串getPostvote（）{
        返回postvote;
    }    公共字符串getPosttitle（）{
        返回posttitle;
    }
    公众诠释getIconID（）{
        返回iconID;
    }
 

  

TheWallFragment.java

 公共类TheWallFragment扩展android.support.v4.app.ListFragment {
    清单＆LT;岗位＆GT; myPosts =新的ArrayList＆LT;邮电GT;（）;
    私有String [] strListView;
    私人的ListView myListView;
    私人诠释数目;
    公共查看onCreateView（LayoutInflater充气器，容器的ViewGroup，
                             捆绑savedInstanceState）{
        查看rootView = inflater.inflate（R.layout.wall_layout，集装箱，FALSE）;
        返回rootView;
    }
}
 

  

activity_main.xml中

 ＆LT; android.support.v4.view.ViewPager的xmlns：机器人=htt​​p://schemas.android.com/apk/res/android
的xmlns：工具=htt​​p://schemas.android.com/tool​​s机器人：ID =@ + ID /寻呼机
机器人：layout_width =match_parent机器人：layout_height =match_parent
工具：上下文=。MainActivity/＆GT;
 

  

AndroidManifest.xml中

 ＆LT;？XML版本=1.0编码=UTF-8＆GT？;
＆LT;清单的xmlns：机器人=htt​​p://schemas.android.com/apk/res/android
    包=com.gnumbu.errolgreen.testing＆GT;    ＆lt;应用
        机器人：allowBackup =真
        机器人：图标=@的mipmap / ic_launcher
        机器人：标签=@字符串/ APP_NAME
        机器人：主题=@风格/ AppTheme＆GT;
        ＆LT;活动
            机器人：名字=。MainActivity
            机器人：标签=@字符串/ APP_NAME＆GT;
            ＆所述;意图滤光器＆gt;
                ＆lt;作用机器人：名字=android.intent.action.MAIN/＆GT;                ＆LT;类机器人：名字=android.intent.category.LAUNCHER/＆GT;
            ＆所述; /意图滤光器＆gt;
        ＆LT; /活性GT;
＆LT;活动
    机器人：名字=。NotMainActivity＆GT;
    ＆LT; /活性GT;
    ＆LT; /用途＆gt;＆LT; /清单＆GT;
 

  

item_view.xml

 ＆LT;？XML版本=1.0编码=UTF-8＆GT？;
＆LT;的RelativeLayout的xmlns：机器人=htt​​p://schemas.android.com/apk/res/android
    机器人：layout_width =match_parent机器人：layout_height =match_parent＆GT;    ＆LT; ImageView的
        机器人：layout_width =WRAP_CONTENT
        机器人：layout_height =WRAP_CONTENT
        机器人：ID =@ + ID / item_postImage
        机器人：SRC =@绘制/狗
        安卓了maxWidth =80dp
        安卓了minHeight =80dp
        机器人：adjustViewBounds =真
        机器人：layout_marginLeft =14dp
        机器人：layout_marginStart =14dp
        机器人：layout_alignParentTop =真
        机器人：layout_toRightOf =@ + ID / item_upvoteArrow
        机器人：layout_toEndOf =@ + ID / item_upvoteArrow
        机器人：layout_alignBottom =@ + ID / item_downvotearrow/＆GT;    ＆LT;的TextView
        机器人：layout_width =WRAP_CONTENT
        机器人：layout_height =WRAP_CONTENT
        机器人：文字=这是我的狗我的狗是惊人的，给它舔！
        机器人：ID =@ + ID / item_postText
        机器人：paddingStart =5DP
        机器人：layout_above =@ + ID / item_downvotearrow
        机器人：layout_toRightOf =@ + ID / item_postImage
        机器人：layout_toEndOf =@ + ID / item_postImage/＆GT;    ＆LT; ImageView的
        机器人：layout_width =WRAP_CONTENT
        机器人：layout_height =WRAP_CONTENT
        机器人：ID =@ + ID / item_upvoteArrow
        机器人：SRC =@绘制/ upvotearrow
        安卓了maxHeight =24dp
        安卓了maxWidth =24dp
        机器人：adjustViewBounds =真
        机器人：layout_alignParentTop =真
        机器人：layout_alignLeft =@ + ID / item_downvotearrow
        机器人：layout_alignStart =@ + ID / item_downvotearrow
        机器人：可点击=真/＆GT;    ＆LT; ImageView的
        机器人：layout_width =WRAP_CONTENT
        机器人：layout_height =WRAP_CONTENT
        机器人：ID =@ + ID / item_downvotearrow
        机器人：SRC =@绘制/ downvotearrow
        安卓了maxWidth =24dp
        安卓了maxHeight =24dp
        机器人：adjustViewBounds =真
        机器人：layout_marginLeft =9dp
        机器人：layout_marginStart =9dp
        机器人：layout_below =@ + ID / item_postVoteText
        机器人：layout_alignParentLeft =真
        机器人：layout_alignParentStart =真
        机器人：longClickable =假
        机器人：可点击=真/＆GT;    ＆LT;的TextView
        机器人：layout_height =WRAP_CONTENT
        机器人：文字=22
        机器人：ID =@ + ID / item_postVoteText
        安卓了maxHeight =20dp
        机器人：focusableInTouchMode =假
        机器人：知名度=看得见
        机器人：单线=真
        机器人：比重=中心
        机器人：启用=真
        机器人：layout_below =@ + ID / item_upvoteArrow
        机器人：layout_alignLeft =@ + ID / item_upvoteArrow
        机器人：layout_alignStart =@ + ID / item_upvoteArrow
        机器人：nestedScrollingEnabled =假
        机器人：layout_width =WRAP_CONTENT
        机器人：layout_toStartOf =@ + ID / item_postImage/＆GT;＆LT; / RelativeLayout的＆GT;
 

  

wall_layout.xml

 ＆LT;？XML版本=1.0编码=UTF-8＆GT？;
＆LT; LinearLayout中的xmlns：机器人=htt​​p://schemas.android.com/apk/res/android
    机器人：方向=垂直的android：layout_width =match_parent
    机器人：layout_height =match_parent＆GT;    ＆LT;的TextView
        机器人：layout_width =WRAP_CONTENT
        机器人：layout_height =WRAP_CONTENT
        机器人：文字=新文本
        机器人：ID =@ + ID / TextView的
        机器人：layout_gravity =CENTER_HORIZONTAL/＆GT;    ＆LT; ListView控件
        机器人：ID =@机器人：ID /列表
        机器人：layout_width =WRAP_CONTENT
        机器人：layout_height =WRAP_CONTENT
            /＆GT;
＆LT; / LinearLayout中＆GT;
 

  

错误日志

 显示java.lang.NullPointerException：尝试对空对象引用调用虚拟方法无效android.widget.ListView.setAdapter（android.widget.ListAdapter）'
            在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2298）
            在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2360）
            在android.app.ActivityThread.access $ 800（ActivityThread.java:144）
            在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1278）
            在android.os.Handler.dispatchMessage（Handler.java:102）
            在android.os.Looper.loop（Looper.java:135）
            在android.app.ActivityThread.main（ActivityThread.java:5223）
            在java.lang.reflect.Method.invoke（本机方法）
            在java.lang.reflect.Method.invoke（Method.java:372）
            在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:899）
            在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:694）
     显示java.lang.NullPointerException：引起尝试在空对象引用调用虚拟方法无效android.widget.ListView.setAdapter（android.widget.ListAdapter）'
            在com.gnumbu.errolgreen.testing.NotMainActivity.populateListView（NotMainActivity.java:70）
            在com.gnumbu.errolgreen.testing.NotMainActivity.onCreate（NotMainActivity.java:43）
            在android.app.Activity.performCreate（Activity.java:5937）
            在android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1105）
            在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2251）
在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2360）
在android.app.ActivityThread.access $ 800（ActivityThread.java:144）
在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1278）
在android.os.Handler.dispatchMessage（Handler.java:102）
在android.os.Looper.loop（Looper.java:135）
在android.app.ActivityThread.main（ActivityThread.java:5223）
在java.lang.reflect.Method.invoke（本机方法）
在java.lang.reflect.Method.invoke（Method.java:372）
在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:899）
在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:694）
 

  

新的错误

 流程：com.gnumbu.errolgreen.testing，PID：5304
    显示java.lang.NullPointerException：尝试调用虚方法对空对象引用'诠释android.view.View.getImportantForAccessibility（）
            在android.widget.AbsListView.obtainView（AbsListView.java:2360）
            在android.widget.ListView.measureHeightOfChildren（ListView.java:1270）
            在android.widget.ListView.onMeasure（ListView.java:1182）
            在android.view.View.measure（View.java:17430）
            在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:5463）
            在android.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1436）
            在android.widget.LinearLayout.measureVertical（LinearLayout.java:722）
            在android.widget.LinearLayout.onMeasure（LinearLayout.java:613）
            在android.view.View.measure（View.java:17430）
            在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:5463）
            在android.widget.FrameLayout.onMeasure（FrameLayout.java:430）
            在android.view.View.measure（View.java:17430）
            在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:5463）
            在android.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1436）
            在android.widget.LinearLayout.measureVertical（LinearLayout.java:722）
            在android.widget.LinearLayout.onMeasure（LinearLayout.java:613）
            在android.view.View.measure（View.java:17430）
            在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:5463）
            在android.widget.FrameLayout.onMeasure（FrameLayout.java:430）
            在com.android.internal.policy.impl.PhoneWindow $ DecorView.onMeasure（PhoneWindow.java:2560）
            在android.view.View.measure（View.java:17430）
            在android.view.ViewRootImpl.performMeasure（ViewRootImpl.java:2001）
            在android.view.ViewRootImpl.measureHierarchy（ViewRootImpl.java:1166）
            在android.view.ViewRootImpl.performTraversals（ViewRootImpl.java:1372）
            在android.view.ViewRootImpl.doTraversal（ViewRootImpl.java:1054）
            在android.view.ViewRootImpl $ TraversalRunnable.run（ViewRootImpl.java:5779）
            在android.view.Choreographer $ CallbackRecord.run（Choreographer.java:767）
            在android.view.Choreographer.doCallbacks（Choreographer.java:580）
            在android.view.Choreographer.doFrame（Choreographer.java:550）
            在android.view.Choreographer $ FrameDisplayEventReceiver.run（Choreographer.java:753）
            在android.os.Handler.handleCallback（Handler.java:739）
            在android.os.Handler.dispatchMessage（Handler.java:95）
            在android.os.Looper.loop（Looper.java:135）
            在android.app.ActivityThread.main（ActivityThread.java:5221）
            在java.lang.reflect.Method.invoke（本机方法）
            在java.lang.reflect.Method.invoke（Method.java:372）
            在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:899）
            在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:694）
 

解决方案

NotMainActivity 要求的setContentView 与 R.layout.activity_main 为包含参数 ViewPager ，而不是的ListView 。既然你没有一个ListView申报到布局， findViewById（android.R.id.list）返回null，并且当您尝试访问它（调用 setAdapter ）的 NullPointerException异常被抛出。

在 MyAdapter ，从

变化

 如果（ItemView控件！= NULL）{
      。ItemView控件= getLayoutInflater（）膨胀（R.layout.item_view，父母，假）;
}
 

到

 如果（ItemView控件== NULL）{
      。ItemView控件= getLayoutInflater（）膨胀（R.layout.item_view，父母，假）;
}
 

I am trying to make a list view that contains pictures and text within a fragment that is on a viewpager with tabs, so I can swipe left or right to bring up another fragment.

I'm relatively new to android so what I may be doing could be completely wrong. I can build the project perfectly fine but then when the emulator runs it crashes (log displayed at bottom of page).

I created a separate application and successfully was able to create a list view, but when I try to combine it within a fragment like so, it doesn't work. Here is my following code

MainActivity.java

import java.util.ArrayList;
import java.util.List;
import java.util.Locale;

import android.app.ListFragment;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.app.FragmentPagerAdapter;
import android.os.Bundle;
import android.support.v4.view.ViewPager;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;


public class MainActivity extends ActionBarActivity implements ActionBar.TabListener {

    /**
     * The {@link android.support.v4.view.PagerAdapter} that will provide
     * fragments for each of the sections. We use a
     * {@link FragmentPagerAdapter} derivative, which will keep every
     * loaded fragment in memory. If this becomes too memory intensive, it
     * may be best to switch to a
     * {@link android.support.v4.app.FragmentStatePagerAdapter}.
     */
    SectionsPagerAdapter mSectionsPagerAdapter;

    /**
     * The {@link ViewPager} that will host the section contents.
     */
    ViewPager mViewPager;
   private List<Posts> myPosts = new ArrayList<Posts>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // Set up the action bar.
        final ActionBar actionBar = getSupportActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        // Create the adapter that will return a fragment for each of the three
        // primary sections of the activity.
        mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

        // Set up the ViewPager with the sections adapter.
        mViewPager = (ViewPager) findViewById(R.id.pager);
        mViewPager.setAdapter(mSectionsPagerAdapter);

        // When swiping between different sections, select the corresponding
        // tab. We can also use ActionBar.Tab#select() to do this if we have
        // a reference to the Tab.
        mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
            @Override
            public void onPageSelected(int position) {
                actionBar.setSelectedNavigationItem(position);
            }
        });

        // For each of the sections in the app, add a tab to the action bar.
        for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
            // Create a tab with text corresponding to the page title defined by
            // the adapter. Also specify this Activity object, which implements
            // the TabListener interface, as the callback (listener) for when
            // this tab is selected.
            actionBar.addTab(
                    actionBar.newTab()
                            .setText(mSectionsPagerAdapter.getPageTitle(i))
                            .setTabListener(this));

        }

         Intent intent = new Intent(MainActivity.this, NotMainActivity.class);
        startActivity(intent);
        finish();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
        // When the given tab is selected, switch to the corresponding page in
        // the ViewPager.
        mViewPager.setCurrentItem(tab.getPosition());
    }

    @Override
    public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
    }

    @Override
    public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
    }
    /**
     * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
     * one of the sections/tabs/pages.
     */
    public class SectionsPagerAdapter extends FragmentPagerAdapter {

        public SectionsPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int position) {
            // getItem is called to instantiate the fragment for the given page.
            // Return a PlaceholderFragment (defined as a static inner class below).
            switch (position){
                case 0:
                    return new TheWallFragment();
                case 1:
                    return new PeekFragment();
                case 2:
                    return new CameraFragment();
                default:
                    break;

            }

            return PlaceholderFragment.newInstance(position + 1);
        }




        @Override
        public int getCount() {
            // Show 3 total pages.
            return 3;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            Locale l = Locale.getDefault();
            switch (position) {
                case 0:
                    return getString(R.string.title_section1).toUpperCase(l);
                case 1:
                    return getString(R.string.title_section2).toUpperCase(l);
                case 2:
                    return getString(R.string.title_section3).toUpperCase(l);
            }
            return null;
        }
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {
        /**
         * The fragment argument representing the section number for this
         * fragment.
         */
        private static final String ARG_SECTION_NUMBER = "section_number";

        /**
         * Returns a new instance of this fragment for the given section
         * number.
         */
        public static PlaceholderFragment newInstance(int sectionNumber) {
            PlaceholderFragment fragment = new PlaceholderFragment();
            Bundle args = new Bundle();
            args.putInt(ARG_SECTION_NUMBER, sectionNumber);
            fragment.setArguments(args);
            return fragment;
        }

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.wall_layout, container, false);

            return rootView;
        }
    }

}

NotMainActivity.java

public class NotMainActivity extends FragmentActivity {

    private List<Posts> myPosts = new ArrayList<Posts>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        populatePostList();
        populateListView();

       registerClickCallBack();
        System.out.print("Main Activity Started");



    }


    private void populatePostList()     {
        myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog));
        myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog));
        myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog));
        myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog));
        myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog));
        myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog));
        myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog));
        myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog));



    }

    private void populateListView() {
        ArrayAdapter<Posts> adapter = new MyListAdapter();
        ListView list = (ListView) findViewById(android.R.id.list);
        list.setAdapter(adapter);

        }


    //Handles clicks on the list items
    private void registerClickCallBack(){
        ListView list = (ListView) findViewById(android.R.id.list);
        list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Posts clickedPost = myPosts.get(position);
                String message = "You clicked" + position
                        +"Location of post is" + clickedPost.getPostlocation();
                Toast.makeText(NotMainActivity.this, message, Toast.LENGTH_LONG).show();
            }
        });
    }


    private class MyListAdapter extends ArrayAdapter<Posts> {
        public MyListAdapter() {
            super(NotMainActivity.this, R.layout.item_view, myPosts);
        }


        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            // Make sure we have a view to work with {may have given null}
            View itemView = convertView;
            if (itemView != null) {
                itemView = getLayoutInflater().inflate(R.layout.item_view, parent, false);
            }
            // Find the post to work with.
            Posts currentPost = myPosts.get(position);


            //Fill the view
            ImageView imageView = (ImageView)itemView.findViewById(R.id.item_postImage);
            imageView.setImageResource(currentPost.getIconID());

            //Fill in Title

            TextView titleText = (TextView) itemView.findViewById(R.id.item_postText);
            titleText.setText(currentPost.getPosttitle());

            //Set Vote Number
            TextView voteText = (TextView) itemView.findViewById(R.id.item_postVoteText);
            voteText.setText(currentPost.getPostvote());



            return itemView;
        }

    }

}

Posts.java

public class Posts {
    private String postlocation;
    private String postvote;
    private String posttitle;
    private int iconID;

    public Posts(String postlocation, String postvote, String posttitle, int iconID) {
        this.postlocation = postlocation;
        this.postvote = postvote;
        this.posttitle = posttitle;
        this.iconID = iconID;
    }







    public String getPostlocation() {
        return postlocation;
    }

    public String getPostvote() {
        return postvote;
    }

    public String getPosttitle() {
        return posttitle;
    }
    public int getIconID() {
        return iconID;
    }

TheWallFragment.java

public class TheWallFragment extends android.support.v4.app.ListFragment {
    List<Posts> myPosts = new ArrayList<Posts>();
    private String[] strListView;
    private ListView myListView;
    private int number;
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.wall_layout, container, false);
        return rootView;
    }


}

activity_main.xml

<android.support.v4.view.ViewPager      xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:id="@+id/pager"
android:layout_width="match_parent" android:layout_height="match_parent"
tools:context=".MainActivity" />

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.gnumbu.errolgreen.testing" >

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
<activity
    android:name=".NotMainActivity">
    </activity>
    </application>

</manifest>

item_view.xml

    <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent">

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/item_postImage"
        android:src="@drawable/dog"
        android:maxWidth="80dp"
        android:minHeight="80dp"
        android:adjustViewBounds="true"
        android:layout_marginLeft="14dp"
        android:layout_marginStart="14dp"
        android:layout_alignParentTop="true"
        android:layout_toRightOf="@+id/item_upvoteArrow"
        android:layout_toEndOf="@+id/item_upvoteArrow"
        android:layout_alignBottom="@+id/item_downvotearrow" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="This is my dog! My Dog is amazing, give it a lick!"
        android:id="@+id/item_postText"
        android:paddingStart="5dp"
        android:layout_above="@+id/item_downvotearrow"
        android:layout_toRightOf="@+id/item_postImage"
        android:layout_toEndOf="@+id/item_postImage" />

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/item_upvoteArrow"
        android:src="@drawable/upvotearrow"
        android:maxHeight="24dp"
        android:maxWidth="24dp"
        android:adjustViewBounds="true"
        android:layout_alignParentTop="true"
        android:layout_alignLeft="@+id/item_downvotearrow"
        android:layout_alignStart="@+id/item_downvotearrow"
        android:clickable="true" />

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/item_downvotearrow"
        android:src="@drawable/downvotearrow"
        android:maxWidth="24dp"
        android:maxHeight="24dp"
        android:adjustViewBounds="true"
        android:layout_marginLeft="9dp"
        android:layout_marginStart="9dp"
        android:layout_below="@+id/item_postVoteText"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:longClickable="false"
        android:clickable="true" />

    <TextView
        android:layout_height="wrap_content"
        android:text="22"
        android:id="@+id/item_postVoteText"
        android:maxHeight="20dp"
        android:focusableInTouchMode="false"
        android:visibility="visible"
        android:singleLine="true"
        android:gravity="center"
        android:enabled="true"
        android:layout_below="@+id/item_upvoteArrow"
        android:layout_alignLeft="@+id/item_upvoteArrow"
        android:layout_alignStart="@+id/item_upvoteArrow"
        android:nestedScrollingEnabled="false"
        android:layout_width="wrap_content"
        android:layout_toStartOf="@+id/item_postImage" />

</RelativeLayout>

wall_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="New Text"
        android:id="@+id/textView"
        android:layout_gravity="center_horizontal" />

    <ListView
        android:id="@android:id/list"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
            />
</LinearLayout>

Error Log

 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5223)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
            at com.gnumbu.errolgreen.testing.NotMainActivity.populateListView(NotMainActivity.java:70)
            at com.gnumbu.errolgreen.testing.NotMainActivity.onCreate(NotMainActivity.java:43)
            at android.app.Activity.performCreate(Activity.java:5937)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5223)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

New Error

 Process: com.gnumbu.errolgreen.testing, PID: 5304
    java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getImportantForAccessibility()' on a null object reference
            at android.widget.AbsListView.obtainView(AbsListView.java:2360)
            at android.widget.ListView.measureHeightOfChildren(ListView.java:1270)
            at android.widget.ListView.onMeasure(ListView.java:1182)
            at android.view.View.measure(View.java:17430)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
            at android.view.View.measure(View.java:17430)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
            at android.view.View.measure(View.java:17430)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
            at android.view.View.measure(View.java:17430)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2560)
            at android.view.View.measure(View.java:17430)
            at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2001)
            at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1166)
            at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1372)
            at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
            at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
            at android.view.Choreographer.doCallbacks(Choreographer.java:580)
            at android.view.Choreographer.doFrame(Choreographer.java:550)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

解决方案

NotMainActivity calls setContentView with R.layout.activity_main as parameter that contains a ViewPager and not a ListView. Since you don't have a ListView declare in to that layout, findViewById(android.R.id.list) returns null, and when you try access it (calling setAdapter) the NullPointerException is thrown.

in your MyAdapter, change from

if (itemView != null) {
      itemView = getLayoutInflater().inflate(R.layout.item_view, parent, false);
}

to

if (itemView == null) {
      itemView = getLayoutInflater().inflate(R.layout.item_view, parent, false);
}

这篇关于试图调用虚拟方法无效android.widget.ListView.setAdapter的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！