tabHost.setup()给出空指针异常(安卓工作室) [英] tabHost.setup() gives null pointer exception (Android studio)
问题描述
我有一个非常简单的应用程序,它仅仅是上有一个标签视图的活动。
I have a very simple app which is just an activity with a tab view on it.
我已经初始化,铸造一切理所应当的,但我不断地得到它总是链接回空指针错误
I have initialised and casted everything to as it should be but am continually getting a null pointer error which always links back to
tabHost.setup();
tabHost.setup();
我使用的机器人工作室是新来的Java。这个问题已经被问了很多在这里,但所有的答案,只是说包括设置(),我已经做到了。
I am using android studio and am new to java. This question has been asked a lot on here but all answers just say to include the setup() and I have already done that.
下面是我的.java文件:
Here is my .java file:
package com.example.app;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.os.Build;
import android.widget.TabHost;
public class MainActivity extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
TabHost tabHost = (TabHost) findViewById(R.id.tabHost);
tabHost.setup();
TabHost.TabSpec spec1, spec2, spec3;
spec1 = tabHost.newTabSpec("spec1");
spec1.setContent(R.id.tab1);
spec1.setIndicator("Tab1");
tabHost.addTab(spec1);
spec2 = tabHost.newTabSpec("spec2");
spec2.setContent(R.id.tab2);
spec2.setIndicator("Tab2");
tabHost.addTab(spec2);
spec3 = tabHost.newTabSpec("spec3");
spec3.setContent(R.id.tab3);
spec3.setIndicator("Tab3");
tabHost.addTab(spec3);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.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();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
}
}
之间我的code和一些在线教程,唯一的区别是公共类MainActivity延伸到ActionBarActivity而不仅仅是活动。我甚至没有做到这一点,这是默认的,当我创建了一个空白的项目。
The only difference between my code and some online tutorials is the public class MainActivity extending to ActionBarActivity and not just Activity. I didn't even do this, it was default when i created a blank project.
XML文件是下面也:
The XML file is below also:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context="com.example.app.MainActivity$PlaceholderFragment">
<TabHost
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/tabHost"
android:layout_alignParentTop="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true">
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical">
<TabWidget
android:id="@android:id/tabs"
android:layout_width="fill_parent"
android:layout_height="wrap_content"></TabWidget>
<FrameLayout
android:id="@android:id/tabcontent"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<LinearLayout
android:id="@+id/tab1"
android:layout_width="fill_parent"
android:layout_height="fill_parent"></LinearLayout>
<LinearLayout
android:id="@+id/tab2"
android:layout_width="fill_parent"
android:layout_height="fill_parent"></LinearLayout>
<LinearLayout
android:id="@+id/tab3"
android:layout_width="fill_parent"
android:layout_height="fill_parent"></LinearLayout>
</FrameLayout>
</LinearLayout>
</TabHost>
推荐答案
这行表明您已经创建了TabHost是 fragment_main.xml
这是用来布局目录中通过PlaceholderFragment
This Line shows that the TabHost you have created is in fragment_main.xml
inside layout directory which is used by PlaceholderFragment
tools:context="com.example.app.MainActivity$PlaceholderFragment"
但你发现你的TabHost在 activity_main.xml
移动你的code从的onCreate()
到 onCreateView
PlaceholderFragment的,低于同级别,如果你使用默认模板自带的像
Move your code from onCreate()
to onCreateView
of PlaceholderFragment, below in same class if you are using default template comes with AS like
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
TabHost tabHost = (TabHost) rootView.findViewById(R.id.tabHost);
tabHost.setup();
TabHost.TabSpec spec1, spec2, spec3;
spec1 = tabHost.newTabSpec("spec1");
spec1.setContent(R.id.tab1);
spec1.setIndicator("Tab1");
tabHost.addTab(spec1);
spec2 = tabHost.newTabSpec("spec2");
spec2.setContent(R.id.tab2);
spec2.setIndicator("Tab2");
tabHost.addTab(spec2);
spec3 = tabHost.newTabSpec("spec3");
spec3.setContent(R.id.tab3);
spec3.setIndicator("Tab3");
tabHost.addTab(spec3);
return rootView;
}
或者如果你愿意,你可以将你的TabHost到 activity_main.xml
,以及在不改变Java的code,但我们不建议使用具有很多碎片好处。
Or If you want you can move your TabHost to activity_main.xml
as well without changing the java code but that is not recommended using fragments having a lot of benefits.
选中此使用片段的好处
<一个href="http://stackoverflow.com/questions/21154148/fragment-main-and-activity-main-layouts-in-android-studio/21155124#21155124">fragment_main和activity_main布局在Android的工作室
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