android - ChildFragmentManager.getFragment() 和 NullPointerException

Question

我有一个承载子 fragment 的父 fragment 。 我对我的应用程序进行了压力测试，通过在开发者选项中选中“不保留 Activity ”，然后按“主页”按钮来强制终止它。

可以看到调用了父fragment的onSaveInstanceState，该函数的代码为:

if (mDetailFragment!=null){
    getChildFragmentManager().putFragment(outState,FRAGMENT_ROUTE,mDetailFragment);
}

然后，当我恢复应用程序时，看到父 fragment 的 onCreate 是使用非空和非空的 savingInstanceState 调用的，我可以看到包含索引 FRAGMENT_ROUTE 的包。但是，当我调用 getFragment 时，它总是崩溃。代码如下:

if (savedInstanceState == null) {
    mDetailFragment = new RouteFragment();
    fragmentManager.beginTransaction().replace(R.id.v4_fragment_route, mDetailFragment).commit();
} else {
    //first try to find the fragment in a normal way
    mDetailFragment = (RouteFragment) fragmentManager.findFragmentById(R.id.v4_fragment_route);
    //if cannot, then use getFragment
    if (mDetailFragment== null){
        mDetailFragment = (RouteFragment) fragmentManager.getFragment(savedInstanceState,FRAGMENT_ROUTE);
    }
}

崩溃日志如下，看起来索引列表是空的。我缺少什么？谢谢

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference
            at android.support.v4.app.FragmentManagerImpl.getFragment(FragmentManager.java:583)
            at com.myapp.android.appname.fragment.HomeFragment.onCreate(HomeFragment.java:170)
            at android.support.v4.app.Fragment.performCreate(Fragment.java:1764)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:915)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1127)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1109)
            at android.support.v4.app.FragmentManagerImpl.dispatchCreate(FragmentManager.java:1913)
            at android.support.v4.app.FragmentActivity.onCreate(FragmentActivity.java:267)
            at android.support.v7.app.ActionBarActivity.onCreate(ActionBarActivity.java:123)
            at com.buzzhives.android.tripplanner.ProgressEnabledActivity.onCreate(ProgressEnabledActivity.java:25)
            at com.buzzhives.android.tripplanner.MainActivity.onCreate(MainActivity.java:73)
            at android.app.Activity.performCreate(Activity.java:5934)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1279)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5223)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

Answer 1

fragment (无 fragment )已创建。在任何 fragment 存在或崩溃之前，您不能调用 getFragment。它可能不应该(应该返回 null)，但它是一个错误。