非法状态更改语言时显示异常

Question

我正在开发一个应用程序，它有一个Activity和两个Fragments，其中第二个Fragments是第一个的孩子。当我进入第二个Fragments并将语言从法语更改为英语时，系统会抛出IllegalStateException当我返回应用程序时，它说Fragments已经存在。

 Caused by: java.lang.IllegalStateException: Fragment already added 
SettingsFragment{d25576a #3 id=0x1020011}
android.support.v4.app.FragmentManagerImpl.addFragment
FragmentManager.java, line 1679
android.support.v4.app.BackStackRecord.executePopOps
BackStackRecord.java, line 781
android.support.v4.app.FragmentManagerImpl.executeOps
FragmentManager.java, line 2360
android.support.v4.app.FragmentManagerImpl.executeOpsTogether
FragmentManager.java, line 2149
android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps
FragmentManager.java, line 2103
android.support.v4.app.FragmentManagerImpl.execPendingActions
FragmentManager.java, line 2013
android.support.v4.app.FragmentController.execPendingActions
FragmentController.java, line 388
android.support.v4.app.FragmentActivity.onStart
FragmentActivity.java, line 607
android.support.v7.app.AppCompatActivity.onStart
AppCompatActivity.java, line 178
android.app.Instrumentation.callActivityOnStart
Instrumentation.java, line 1256
android.app.Activity.performStart
Activity.java, line 6972
android.app.ActivityThread.performLaunchActivity

Answer 1

您应该阅读堆栈跟踪的第一行：

非法状态异常：已添加片段

如果添加片段两次，请检查您的代码。

Answer 2

当您在

onCreate()活动中添加片段时，请尝试检查if (savedInstanceState == null)：

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    if (savedInstanceState == null) {
        getSupportFragmentManager()
                .beginTransaction()
                .add(R.id.main_frame_layout, new SettingsFragment())
                .commit();
    }
}

Answer 3

在添加片段之前，您应该检查此片段是否尚未添加

Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.container);
        if (fragment == null) {
            MyFragment myFragment = new MyFragment();
            getSupportFragmentManager().beginTransaction().add(R.id.container, myFragment).commit();
        }