我有一个ActivityFragments三个Buttons和FragmentOne , FragmentTwo , FragmentThree类。当Button1按下它必须显示 FragmentOne并隐藏FragmentTwo和FragmentThree 。如果Button2按下它必须显示 FragmentTwo并隐藏FragmentOne和FragmentThree 。类似地，如果 Button3按下它必须显示 FragmentThree并隐藏FragmentTwo和FragmentOne 。我的代码无法显示 NullPointerException E/AndroidRuntime(362): at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:656)
Logcat:
04-08 08:10:31.830: E/AndroidRuntime(362): FATAL EXCEPTION: main
04-08 08:10:31.830: E/AndroidRuntime(362): java.lang.NullPointerException
04-08 08:10:31.830: E/AndroidRuntime(362): at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:656)
04-08 08:10:31.830: E/AndroidRuntime(362): at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1444)
04-08 08:10:31.830: E/AndroidRuntime(362): at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:429)
04-08 08:10:31.830: E/AndroidRuntime(362): at android.os.Handler.handleCallback(Handler.java:587)
04-08 08:10:31.830: E/AndroidRuntime(362): at android.os.Handler.dispatchMessage(Handler.java:92)
04-08 08:10:31.830: E/AndroidRuntime(362): at android.os.Looper.loop(Looper.java:123)
04-08 08:10:31.830: E/AndroidRuntime(362): at android.app.ActivityThread.main(ActivityThread.java:4627)
04-08 08:10:31.830: E/AndroidRuntime(362): at java.lang.reflect.Method.invokeNative(Native Method)
04-08 08:10:31.830: E/AndroidRuntime(362): at java.lang.reflect.Method.invoke(Method.java:521)
04-08 08:10:31.830: E/AndroidRuntime(362): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
04-08 08:10:31.830: E/AndroidRuntime(362): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
04-08 08:10:31.830: E/AndroidRuntime(362): at dalvik.system.NativeStart.main(Native Method)
这是代码:MainActivity.java
public class MainActivity extends FragmentActivity implements OnClickListener {
Button b1, b2, b3;
Fragment f1, f2, f3;
FragmentManager manager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
b1 = (Button) findViewById(R.id.button1);
b2 = (Button) findViewById(R.id.button2);
b3 = (Button) findViewById(R.id.button3);
b1.setOnClickListener(this);
b2.setOnClickListener(this);
b3.setOnClickListener(this);
manager = getSupportFragmentManager();
f1 = manager.findFragmentById(R.id.first);
f2 = manager.findFragmentById(R.id.second);
f2 = manager.findFragmentById(R.id.third);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.button1:
if(b1.isPressed()){
FragmentTransaction transaction = getSupportFragmentManager()
.beginTransaction();
transaction.hide(f2);
transaction.hide(f3);
transaction.show(f1);
transaction.commit();
}
break;
case R.id.button2:
if(b2.isPressed()){
FragmentTransaction transaction1 = getSupportFragmentManager()
.beginTransaction();
transaction1.hide(f1);
transaction1.hide(f3);
transaction1.show(f2);
transaction1.commit();
}
break;
case R.id.button3:
if(b3.isPressed()){
FragmentTransaction transaction2 = getSupportFragmentManager()
.beginTransaction();
transaction2.hide(f1);
transaction2.hide(f2);
transaction2.show(f3);
transaction2.commit();
}
break;
}
}
}
public class FirstFragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.first, container, false);
return view;
}
}
public class SecondFragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.second, container, false);
return view;
}
}
public class Third extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.third, container, false);
return view;
}
}
布局文件:main.xml
<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:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:text="Button 1" />
<Button
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="@+id/button1"
android:layout_toRightOf="@+id/button1"
android:text="Button 2" />
<Button
android:id="@+id/button3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="@+id/button2"
android:layout_toRightOf="@+id/button2"
android:text="Button 3" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/button1"
android:layout_below="@+id/button1"
android:orientation="horizontal" >
<fragment
android:id="@+id/first"
android:layout_width="match_parent"
android:layout_height="wrap_content"
class="com.fragmentworks.FirstFragment" />
<fragment
android:id="@+id/second"
android:layout_width="match_parent"
android:layout_height="wrap_content"
class="com.fragmentworks.SecondFragment" />
<fragment
android:id="@+id/third"
android:layout_width="match_parent"
android:layout_height="wrap_content"
class="com.fragmentworks.Third" />
</LinearLayout>
最佳答案
您有一个拼写错误:
f1 = manager.findFragmentById(R.id.first);
f2 = manager.findFragmentById(R.id.second);
f2 = manager.findFragmentById(R.id.third);
最后一行应该是f3 =....
阿里。
关于android - fragment 管理器上的空指针异常，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/15870542/