Question

我正在尝试学习android中的片段，并在活动暂停时尝试用Activity onPause()方法中的另一个替换片段。

onPause方法的代码是： -

public void onPause(){
    super.onPause();
    System.out.println("ActivityA-onPause()-1");
    ArticleListFragment temp=(ArticleListFragment) getFragmentManager().findFragmentById(R.id.article_list_fragment);
    System.out.println("ActivityA-onPause()-2");
    if(!temp.isAdded()){    //problem
        System.out.println("ActivityA-onPause()-3");
        fragmentTransaction.replace(R.id.activity_a, articleReaderFragment, new String("readerFragment"));
        System.out.println("ActivityA-onPause()-4");
    }
    System.out.println("ActivityA-onPause()-5");
}

当我在设备上执行应用程序时，onPause（）执行但只打印到“Activity-onPause（） - 2”但不打印“Activity-onPause（） - 3”。

我收到错误日志： -

06-13 00:25:10.946: I/System.out(17974): ActivityA-onPause()-1
06-13 00:25:10.946: I/System.out(17974): ActivityA-onPause()-2
06-13 00:25:10.946: D/AndroidRuntime(17974): Shutting down VM
06-13 00:25:10.946: W/dalvikvm(17974): threadid=1: thread exiting with uncaught exception (group=0xb4e04908)
06-13 00:25:10.961: E/AndroidRuntime(17974): FATAL EXCEPTION: main
06-13 00:25:10.961: E/AndroidRuntime(17974): java.lang.RuntimeException: Unable to pause activity {com.pravesh.fragments/com.pravesh.fragments.ActivityA}: java.lang.NullPointerException
06-13 00:25:10.961: E/AndroidRuntime(17974):    at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3016)
06-13 00:25:10.961: E/AndroidRuntime(17974):    at android.app.ActivityThread.performPauseActivity(ActivityThread.java:2971)
06-13 00:25:10.961: E/AndroidRuntime(17974):    at android.app.ActivityThread.handlePauseActivity(ActivityThread.java:2949)
06-13 00:25:10.961: E/AndroidRuntime(17974):    at android.app.ActivityThread.access$800(ActivityThread.java:141)
06-13 00:25:10.961: E/AndroidRuntime(17974):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1251)
06-13 00:25:10.961: E/AndroidRuntime(17974):    at android.os.Handler.dispatchMessage(Handler.java:99)
06-13 00:25:10.961: E/AndroidRuntime(17974):    at android.os.Looper.loop(Looper.java:137)
06-13 00:25:10.961: E/AndroidRuntime(17974):    at android.app.ActivityThread.main(ActivityThread.java:5039)
06-13 00:25:10.961: E/AndroidRuntime(17974):    at java.lang.reflect.Method.invokeNative(Native Method)
06-13 00:25:10.961: E/AndroidRuntime(17974):    at java.lang.reflect.Method.invoke(Method.java:511)
06-13 00:25:10.961: E/AndroidRuntime(17974):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
06-13 00:25:10.961: E/AndroidRuntime(17974):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
06-13 00:25:10.961: E/AndroidRuntime(17974):    at dalvik.system.NativeStart.main(Native Method)
06-13 00:25:10.961: E/AndroidRuntime(17974): Caused by: java.lang.NullPointerException
06-13 00:25:10.961: E/AndroidRuntime(17974):    at com.pravesh.fragments.ActivityA.onPause(ActivityA.java:37)
06-13 00:25:10.961: E/AndroidRuntime(17974):    at android.app.Activity.performPause(Activity.java:5206)
06-13 00:25:10.961: E/AndroidRuntime(17974):    at android.app.Instrumentation.callActivityOnPause(Instrumentation.java:1226)
06-13 00:25:10.961: E/AndroidRuntime(17974):    at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3002)
06-13 00:25:10.961: E/AndroidRuntime(17974):    ... 12 more

我能理解的是它给出了一个空指针异常，但我不知道为什么。

Answer 1

尝试在替换片段并执行所有其他操作后调用super.onPause。

Android：替换Activity的onPause（）方法中的片段会产生NullPointerException

1 个答案: