尝试在空对象引用调用虚拟方法无效android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' [英] Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' on a null object reference
问题描述
我试图采用了android材料设计来实现滑动的拉布局。但它给了我 NullPointerException异常
。这里是我的code迄今:
MainActivity.java
公共类MainActivity扩展ActionBarActivity {
私人工具栏工具栏;
私人ViewPager寻呼机;
私人SlidingTabLayout nLayout;
@覆盖
保护无效的onCreate(捆绑savedInstanceState){
super.onCreate(savedInstanceState); 的setContentView(R.layout.activity_main_appbar);
工具栏=(栏)findViewById(R.id.app_bar);
setSupportActionBar(工具栏);
getSupportActionBar()setDisplayShowHomeEnabled(真)。 NavigationDrawerFragment drawerFragment =(NavigationDrawerFragment)
。getSupportFragmentManager()findFragmentById(R.id.navigation_drawer_fragment);
drawerFragment.setUp(R.id.navigation_drawer_fragment,(DrawerLayout)findViewById(R.id.drawer_layout),工具栏);
寻呼机=(ViewPager)findViewById(R.id.pager);
pager.setAdapter(新MyPagerAdapter(getSupportFragmentManager())); nLayout =(SlidingTabLayout)findViewById(R.id.tabs);
nLayout.setViewPager(寻呼机);
} @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;
}
如果(ID == R.id.navigate){
startActivity(新意图(这一点,SubActivity.class)); } 返回super.onOptionsItemSelected(项目);
} 类MyPagerAdapter扩展FragmentPagerAdapter { 串片[]; 公共MyPagerAdapter(FragmentManager FM){
超(FM);
标签= getResources()getStringArray(R.array.tabs)。
} @覆盖
公共片段的getItem(INT位置){
MyFragment myFragment = MyFragment.getInstance(位置);
返回myFragment;
} @覆盖
公共CharSequence的getPageTitle(INT位置){
返回标签[位置]
} @覆盖
公众诠释的getCount(){
返回3;
}
} 公共静态类MyFragment扩展片段{
私人TextView的TextView的; 公共静态MyFragment的getInstance(INT位置){
MyFragment myFragment =新MyFragment();
捆绑ARGS =新包();
args.putInt(位置,位置);
myFragment.setArguments(参数);
返回myFragment;
} @Nullable
@覆盖
公共查看onCreateView(LayoutInflater充气器,容器的ViewGroup,捆绑savedInstanceState){
查看布局= inflater.inflate(R.layout.fragment_my,集装箱,FALSE);
的TextView =(TextView中)layout.findViewById(R.id.position);
捆绑包= getArguments();
如果(捆绑!= NULL){
textView.setText(选定的页面是+ bundle.getInt(位置));
}
返回布局;
}
}
}
activity_main.xml中
<的LinearLayout
机器人:layout_width =match_parent
机器人:layout_height =match_parent
机器人:方向=垂直
工具:上下文=carsaleapp.shanaka.com.carsaleapp.MainActivity> <包括
机器人:ID =@ + ID / app_bar
布局=@布局/ app_bar/> < app.shanaka.tabs.SlidingTabLayout
机器人:ID =@ + ID /标签
机器人:layout_width =match_parent
机器人:layout_height =WRAP_CONTENT/>
< android.support.v4.view.ViewPager
机器人:ID =@ + ID /寻呼机
机器人:layout_width =match_parent
机器人:layout_height =0dp
机器人:layout_weight =1/>
< / LinearLayout中>
这是我得到了我的运行应用程序后错误:
了java.lang.RuntimeException:无法启动活动ComponentInfo {carsaleapp.shanaka.com.carsaleapp / carsaleapp.shanaka.com.carsaleapp.MainActivity}:显示java.lang.NullPointerException:尝试调用虚拟方法无效android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)对空对象引用
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: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)
显示java.lang.NullPointerException:引起尝试在空对象引用调用虚拟方法无效android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)'
在carsaleapp.shanaka.com.carsaleapp.MainActivity.onCreate(MainActivity.java:42)
在android.app.Activity.performCreate(Activity.java:5933)
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: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)
他们继续说,寻呼机
对象为null。但对我来说我已经正确设置。
寻呼机=(ViewPager)findViewById(R.id.pager);
您在 activity_main.xml中
视图寻呼机,而你的活动布局
的setContentView(R.layout.activity_main_appbar)
。你不必观点寻呼机在 activity_main_appbar.xml
。
findViewById
查找在当前视图层次视图。我想这应该是的setContentView(R.layout.activity_main);
,但做检查你有包含的布局有什么意见 app_bar.xml
I'm trying to implement sliding tab layout using android material design. But it gives me NullPointerException
. Here is my code so far:
MainActivity.java
public class MainActivity extends ActionBarActivity {
private Toolbar toolbar;
private ViewPager pager;
private SlidingTabLayout nLayout;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_appbar);
toolbar = (Toolbar) findViewById(R.id.app_bar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayShowHomeEnabled(true);
NavigationDrawerFragment drawerFragment = (NavigationDrawerFragment)
getSupportFragmentManager().findFragmentById(R.id.navigation_drawer_fragment);
drawerFragment.setUp(R.id.navigation_drawer_fragment, (DrawerLayout) findViewById(R.id.drawer_layout), toolbar);
pager = (ViewPager) findViewById(R.id.pager);
pager.setAdapter(new MyPagerAdapter(getSupportFragmentManager()));
nLayout = (SlidingTabLayout) findViewById(R.id.tabs);
nLayout.setViewPager(pager);
}
@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;
}
if (id == R.id.navigate) {
startActivity(new Intent(this, SubActivity.class));
}
return super.onOptionsItemSelected(item);
}
class MyPagerAdapter extends FragmentPagerAdapter {
String tabs[];
public MyPagerAdapter(FragmentManager fm) {
super(fm);
tabs = getResources().getStringArray(R.array.tabs);
}
@Override
public Fragment getItem(int position) {
MyFragment myFragment = MyFragment.getInstance(position);
return myFragment;
}
@Override
public CharSequence getPageTitle(int position) {
return tabs[position];
}
@Override
public int getCount() {
return 3;
}
}
public static class MyFragment extends Fragment {
private TextView textView;
public static MyFragment getInstance(int position) {
MyFragment myFragment = new MyFragment();
Bundle args = new Bundle();
args.putInt("position", position);
myFragment.setArguments(args);
return myFragment;
}
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View layout = inflater.inflate(R.layout.fragment_my, container, false);
textView = (TextView) layout.findViewById(R.id.position);
Bundle bundle = getArguments();
if (bundle != null) {
textView.setText("The page selected is " + bundle.getInt("position"));
}
return layout;
}
}
}
activity_main.xml
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="carsaleapp.shanaka.com.carsaleapp.MainActivity">
<include
android:id="@+id/app_bar"
layout="@layout/app_bar" />
<app.shanaka.tabs.SlidingTabLayout
android:id="@+id/tabs"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<android.support.v4.view.ViewPager
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1" />
</LinearLayout>
This is the error I got after run my application:
java.lang.RuntimeException: Unable to start activity ComponentInfo{carsaleapp.shanaka.com.carsaleapp/carsaleapp.shanaka.com.carsaleapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' 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: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)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' on a null object reference
at carsaleapp.shanaka.com.carsaleapp.MainActivity.onCreate(MainActivity.java:42)
at android.app.Activity.performCreate(Activity.java:5933)
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: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)
They keep on saying that the pager
object is null. But for me I have set it correctly.
pager = (ViewPager) findViewById(R.id.pager);
You have your view pager in activity_main.xml
while your layout for activity is
setContentView(R.layout.activity_main_appbar)
. You do not have view pager in activity_main_appbar.xml
.
findViewById
looks for a view in the current view hierarchy. I guess it should be setContentView(R.layout.activity_main);
but do check what views you have in included layout app_bar.xml
这篇关于尝试在空对象引用调用虚拟方法无效android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)'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!