android - 尝试使用 WatchViewStub 启动 AnimationDrawable 时出现 NullPointerException

Question

我必须为我的 Android Wear 使用 Watchviewstub，这导致我出现 NullpointerException。当我不使用 WatchviewStub 时，AnimationDrawable 工作正常。

基本上我正在尝试按照描述的方式解决它 here .我在阅读这篇文章时也无法得到答案 post .

main_layout.xml

    <?xml version="1.0" encoding="utf-8"?>
<android.support.wearable.view.WatchViewStub

    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/too/white"
    android:padding="1dp"

    android:id="@+id/watch_view_stub"

    android:layout_width="match_parent"
    android:layout_height="match_parent"

    app:rectLayout="@layout/rect_activity_main"
    app:roundLayout="@layout/round_activity_main"

    tools:context=".MainActivity"
    tools:deviceIds="wear">

    </android.support.wearable.view.WatchViewStub>

rect_activity_main.xml

   <?xml version="1.0" encoding="utf-8"?>
<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:keepScreenOn="true"
    android:background="@color/white"
    app:layout_box="all"
    xmlns:app="http://schemas.android.com/tools"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <ImageView
        android:layout_width="40dp"
        android:layout_height="40dp"
        android:layout_marginTop="6dp"
        android:layout_marginRight="2dp"
        android:id="@+id/heart_animation"
        android:layout_gravity="right|top"
        android:src="@drawable/heart_animation"/>

    <TextView
        android:id="@+id/rate"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="15sp"
        android:text="89"
        android:textColor="@color/white"
        android:layout_marginTop="10dp"
        android:layout_marginRight="13dp"
        android:layout_gravity="right|top"/>

</FrameLayout>

drawable/heart_animation.xml

    <?xml version="1.0" encoding="utf-8"?>
<animation-list
    android:id="@+id/heart_animation_drawable"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:oneshot="false">
    <item android:drawable="@drawable/heart_grey" android:duration="500" />
    <item android:drawable="@drawable/heart_red" android:duration="900" />
    <item android:drawable="@drawable/heart_grey" android:duration="200" />
    <item android:drawable="@drawable/heart_red" android:duration="350" />
    <item android:drawable="@drawable/heart_grey" android:duration="200" />
    <item android:drawable="@drawable/heart_red" android:duration="350" />
</animation-list>

主 Activity .java

    ImageView view;
    AnimationDrawable frameAnimation;

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        view = (ImageView) findViewById(R.id.heart_animation);
        view.setBackgroundResource(R.drawable.heart_animation);
        frameAnimation = (AnimationDrawable) view.getBackground();
}

    // Called when Activity becomes visible or invisible to the user
    @Override
    public void onWindowFocusChanged(boolean hasFocus) {
        super.onWindowFocusChanged(hasFocus);
        if (hasFocus) {
            // Starting the animation when in Focus
            frameAnimation.start();
        } else {
            // Stoping the animation when not in Focus
            frameAnimation.stop();
        }
    }

错误:

 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setBackgroundResource(int)' on a null object reference
        at de.denjo.test.MainActivity.onCreate(MainActivity.java:72)

Answer 1

如果你使用WatchViewStub，你不会直接得到你期望的布局内容，你必须获取WatchViewStub对象，并调用setOnLayoutInflatedListener 就可以了。当调用回调时，您可以使用 WatchViewStub 对象来查找您想要的对象。例如

final WatchViewStub stub = (WatchViewStub) findViewById(R.id.watch_view_stub);
stub.setOnLayoutInflatedListener(new WatchViewStub.OnLayoutInflatedListener() {
     @Override
     public void onLayoutInflated(WatchViewStub watchViewStub) {
             view = (ImageView) watchViewStub.findViewById(R.id.heart_animation);
             view.setBackgroundResource(R.drawable.heart_animation);
             frameAnimation = (AnimationDrawable) view.getBackground(); 
     }
 });