java - 获取 Activity 实例

Question

请问一个简单的问题，我完全是初学者 java 和 android 开发人员。调用surfaceChanged时如何在setCameraDisplayOrientation中获取Activity的实例？

public class MyActivity extends Activity
{
    private Camera mCamera;
    private CameraPreview mPreview;
    public final int cameraId = 0;
    public Activity activity = null;

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

    activity = this; 

        // Create an instance of Camera
        mCamera = getCameraInstance();

        // Create our Preview view and set it as the content of our activity.
        mPreview = new CameraPreview(this, mCamera);
        FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
        preview.addView(mPreview);
    }

    public void setCameraDisplayOrientation(Activity activity,
                        int cameraId, android.hardware.Camera camera) {

    }

    public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
    private SurfaceHolder mHolder;
    private Camera mCamera;
    ...
    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        ...
        setCameraDisplayOrientation(activity, cameraId, mCamera);
        ....
    }
    }
}

Answer 1

这是一种使用静态变量避免内存泄漏的方法:对将在 onCreate(Bundle) 方法中设置的 Activity 实例进行静态弱引用。

1. 在你的中学课上写下如下内容:

   public Class SecondClass {
       private static WeakReference<Activity> mActivityRef;
       public static void updateActivity(Activity activity) {
           mActivityRef = new WeakReference<Activity>(activity);
       }
   

2. 然后在 Activity 类的 onCreate(Bundle) 方法中:

   @Override
   onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       SecondClass.updateActivity(this);
       ...
   }
   

3. 以这种方式使用 Activity 实例:

   mActivityRef.get()