Android java cant从另一个类调用一个函数。怎么做？

Question

我正在尝试调用一个函数来阻止来自另一个类的谷歌VR播放器。但每次我收到这个错误：Attempt to invoke virtual method 'void com.thevrplugin.cordovapluginvrplayer.MediaLoader.pause()' on a null object reference我认为我以错误的方式调用它，你会怎么做？也许这只是私人/公共/保护修饰人的混乱？ PS。你可以在这里找到演示项目：https://github.com/StarStep/cordova-vr-help.git所以具有这些功能的类是这样的：

package com.thevrplugin.cordovapluginvrplayer;

...

public class VrVideoActivity extends GvrActivity {

    private static final String TAG = "VrVideoActivity";
    private static final int EXIT_FROM_VR_REQUEST_CODE = 42;
    private GvrView gvrView;
    private Renderer renderer;
    private VideoUiView uiView;
    protected MediaLoader mediaLoader;
    private ControllerManager controllerManager;
    private Controller controller;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mediaLoader = new MediaLoader(this);

        gvrView = new GvrView(this);
        gvrView.setRenderTargetScale(.5f);
        renderer = new Renderer(gvrView);
        gvrView.setEGLConfigChooser(8, 8, 8, 8, 16, 0);
        gvrView.setRenderer(renderer);
        setContentView(gvrView);

    }

    @Override
    protected void onNewIntent(Intent intent) {
        setIntent(intent);
        recreate();
    }

    @Override
    protected void onPause() {
        mediaLoader.pause();
        controllerManager.stop();
        super.onPause();
    }
}

然后从这里调用它

public class VrPlayer extends CordovaPlugin {

    private String play(Context context, JSONArray args) throws JSONException {
        Intent intent = new Intent(context, VrVideoActivity.class);
        intent.setAction(Intent.ACTION_VIEW);
        JSONObject options = args.getJSONObject(0);
        intent.putExtra("src", options.getString("src"));
        intent.putExtra("displayMode", 0);
        intent.putExtra("inputFormat", 0);
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        context.startActivity(intent);
        return "Ok!";
    }

    private String pause(Context context, JSONArray args) throws JSONException {
        (new VideoActivity()).onPause();
        return "true";
    }

}

Answer 1

Activities由Android框架实例化。为了在Activity中调用方法，您需要引用该活动，但这可能会导致memory leak。

请查看Start android activity from cordova plugin

您必须让VrVideoActivity处理所有UI / UX行为，然后返回到您的Cordova WebApp。您需要了解Java和Android开发，尤其是Activity Lifecycle

Answer 2

通过使引用变量和函数静态来解决。

protected MediaLoader mediaLoader;  ---> protected static MediaLoader mediaLoader;
private String pause(Context contex... ---> public static void myPause() 

然后我就能像这样称呼它：VrVideoActivity.myPause();