java.lang.IllegalStateException：片段已添加

我在使用目标 SDK 4.3 编译和运行的 Android 应用程序时遇到问题。该应用程序有两个 Activity，一个 MainActivity（也是启动器 Activity）和一个 SecondActivity。两者都使用 Fragment。为了也支持旧设备，使用支持库。

在以下场景中，会出现“IllegalStateException：片段已添加”错误。

1) 启动应用程序 -> 显示 MainActivity
2）用Intent切换到SecondActivity
3）按主页按钮
4）等待时间较长（以24小时测试）
5) 再次按应用程序图标 -> 异常。如果时间较短，则 SecondActivity 将按预期显示。

我在 Fragment 处理过程中阅读了很多 IllegalStateExceptions，但所有这些都指出了 Replace() 方法的问题。在 Stacktrace 中，我自己的代码从未被调用。

Fragment是在Activity的onCreate()方法中添加的：

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(..);
    ListFragment listFragment = this.getCaptureListFragment();
    FragmentTransaction tx = this.getSupportFragmentManager().beginTransaction();
    tx.add(R.id.MainFragmentContainer, listFragment, "list_fragment_tag");
    tx.commit(); 
}

private ListFragment getListFragment() {
    ListFragment listFragment = (ListFragment) this.getSupportFragmentManager().findFragmentByTag("list_fragment_tag");
    if (listFragment == null) {
        listFragment = new ListFragment();
    }
    return listFragment;
}


java.lang.RuntimeException: Unable to start activity    ComponentInfo{de.myexample.demo/de.myexample.demo.ui.SecondActivity}: java.lang.IllegalStateException: Fragment already added: ListFragment{42283f58 #0 id=0x7f060094 de.myexample.demo.ui.ListFragment}
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
    at android.app.ActivityThread.access$600(ActivityThread.java:141)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:5103)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:525)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
    at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.IllegalStateException: Fragment already added: ListFragment{42283f58 #0 id=0x7f060094 de.myexample.demo.ui.ListFragment}
    at android.support.v4.app.FragmentManagerImpl.addFragment(SourceFile:1175)
    at android.support.v4.app.BackStackRecord.run(SourceFile:616)
    at android.support.v4.app.FragmentManagerImpl.execPendingActions(SourceFile:1460)
    at android.support.v4.app.FragmentActivity.onStart(SourceFile:556)
    at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171)
    at android.app.Activity.performStart(Activity.java:5143)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
    ... 11 more
java.lang.IllegalStateException: Fragment already added: ListFragment{42283f58 #0 id=0x7f060094 de.myexample.demo.ui.ListFragment}
    at android.support.v4.app.FragmentManagerImpl.addFragment(SourceFile:1175)
    at android.support.v4.app.BackStackRecord.run(SourceFile:616)
    at android.support.v4.app.FragmentManagerImpl.execPendingActions(SourceFile:1460)
    at android.support.v4.app.FragmentActivity.onStart(SourceFile:556)
    at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171)
    at android.app.Activity.performStart(Activity.java:5143)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
    at android.app.ActivityThread.access$600(ActivityThread.java:141)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:5103)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:525)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
    at dalvik.system.NativeStart.main(Native Method)

好吧，自己解决了。

我将所有片段放在 onPause() 中，并将状态存储在一些布尔值中。根据该布尔值，片段将被放入 onResume() 中。无论 Activity 在后台运行多长时间，启动都是稳定的。

boolean addList = false;

@Override
protected void onResume() {
    FragmentTransaction tx = this.getSupportFragmentManager().beginTransaction();
    if (this.addList) {
        ListFragment list = this.getListFragment();
        tx.add(R.id.MainFragmentContainer, list, "list_fragment_tag");
    }

    tx.commit();
    super.onResume();

    this.addList = false;   

}

@Override
protected void onPause() {
    this.addList = this.getListFragment().isAdded();
    ...
    if (this.addList) {
        FragmentTransaction tx = this.getSupportFragmentManager().beginTransaction();
        tx.remove(this.getListFragment());
        tx.commit();
    }
    this.getSupportFragmentManager().executePendingTransactions();
    super.onPause();

}

也许这可以帮助遇到同样问题的人