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
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