android - 在 MiniControllerFragment 中调用 super.onCreateView() 时出现 NullPointerException

Question

在我的应用程序中，我正在尝试 to implement a MiniControlFragment当用户决定关闭 ExpandedControlsActivity(Mini Controller 的全屏版本)时显示。我需要以编程方式将其添加到 xml 布局，而不是以声明方式添加。

所以我创建了自己的扩展 MiniControllerFragment 的类:

public class CastControllingFragment extends MiniControllerFragment
{
    @Override
    public View onCreateView(LayoutInflater layoutInflater, ViewGroup viewGroup, Bundle bundle)
    {
        View view = super.onCreateView(layoutInflater, viewGroup, bundle);
        if (view != null) {
            FrameLayout.LayoutParams frameLayoutParams = new FrameLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
            view.setLayoutParams(frameLayoutParams);
        }
        return view;
    }

    public static void show(FragmentActivity activity) {
        FragmentManager fragmentManager = activity.getSupportFragmentManager();
        if (fragmentManager.findFragmentById(R.id.castMiniController) == null)
        {
            View rootView = activity.findViewById(R.id.fragment_container);
            if (rootView instanceof ViewGroup)
            {                    
               fragmentManager.beginTransaction().add(R.id.fragment_container, new CastControllingFragment()).commit();
            }
        }
    }

}

我将其实例化并将其添加到 Activity 的 onResume 回调中的 fragment 事务:

    @Override
    protected void onResume() {
        CastControllingFragment.show(this);
        super.onResume();
    }

这是 Activity 的布局，FrameLayout 作为我的 fragment 的容器:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                xmlns:app="http://schemas.android.com/apk/res-auto"
                android:layout_width="match_parent"
                android:layout_height="match_parent">
    <FrameLayout
        android:id="@+id/fragment_container"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
    </FrameLayout>

</RelativeLayout>

但是，当我的 CastControllingFragment 中的 super.onCreateView() 被调用时，我收到以下错误:

java.lang.RuntimeException: Unable to resume activity java.lang.NullPointerException: Attempt to read from null array at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3400) at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3440) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2713) at android.app.ActivityThread.-wrap12(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6077) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

Caused by: java.lang.NullPointerException: Attempt to read from null array at com.google.android.gms.cast.framework.media.widget.MiniControllerFragment.zza(Unknown Source) at com.google.android.gms.cast.framework.media.widget.MiniControllerFragment.onCreateView(Unknown Source) at com.google.sample.cast.refplayer.CastControllingFragment.onCreateView(CastControllingFragment.java:22) at android.support.v4.app.Fragment.performCreateView(Fragment.java:2087) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1113) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1295) at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:801) at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1682) at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:388) at android.support.v4.app.FragmentActivity.onPostResume(FragmentActivity.java:499) at android.support.v7.app.AppCompatActivity.onPostResume(AppCompatActivity.java:175) at android.app.Activity.performResume(Activity.java:6792) at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3377) at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3440)  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2713)  at android.app.ActivityThread.-wrap12(ActivityThread.java)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)  at android.os.Handler.dispatchMessage(Handler.java:102)  at android.os.Looper.loop(Looper.java:154)  at android.app.ActivityThread.main(ActivityThread.java:6077)  at java.lang.reflect.Method.invoke(Native Method)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

Answer 1

最新的 Cast SDK 发生了变化，导致它与旧版本的 Google Play 服务不兼容(崩溃)。不幸的是，当使用带有过时 GPS 的最新 Cast SDK(或在模拟器上)时，即使是 Cast 示例应用程序也会崩溃。该问题已在此处讨论:https://github.com/googlecast/CastVideos-android/issues/12

解决方案是在初始化任何 cast 组件之前检查 Google Play 服务版本，包括迷你 Controller (即您不能只将迷你 Controller fragment 放入您的 xml 布局文件中 - 您必须动态膨胀它，或者有两个布局文件 - 一个有迷你 Controller ，一个没有迷你 Controller )。

检查GPS版本的代码:

GoogleApiAvailability apiAvailability = GoogleApiAvailability.getInstance();
int resultCode = apiAvailability.isGooglePlayServicesAvailable(context);
isGPSAvailable = (resultCode == ConnectionResult.SUCCESS);

如果结果不是ConnectionResult.SUCCESS，请不要初始化您的MiniControllerFragment。

另外，请记住，使用 new MiniControllerFragment() 实例化 MiniControllerFragment 是不可能的。您必须从 xml 中扩充它，否则您将得到 NullPointerException。

MiniControllerFragment 有两种充气方式:

1. 创建单独的 xml 布局文件并在 Activity.onCreate 中扩充适当的文件:

   setContentView(isGPSAvailable ? R.layout.activity_main_with_controller : R.layout.activity_main_without_controller);
   

2. 在您的布局中创建指向 MiniControllerFragment 的 ViewStub 并仅在您有播放服务时对其进行膨胀。

Activity 布局:

<ViewStub
android:id="@+id/cast_minicontroller"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout="@layout/cast_mini_controller_fragment"
/>

cast_mini_controller_fragment:

<?xml version="1.0" encoding="utf-8"?>
<fragment xmlns:android="http://schemas.android.com/apk/res/android"
          android:id="@+id/castMiniController"
          class="com.google.android.gms.cast.framework.media.widget.MiniControllerFragment"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:visibility="gone"/>

在您的 Activity onCreate() 中的代码:

ViewStub miniControllerStub = (ViewStub) findViewById(R.id.cast_minicontroller);
if (isGPSAvailable) {
    miniControllerStub.inflate();
}

我更喜欢 ViewStub 方法，因为它不会重复您的布局。