获取活动实例 [英] Get activity instance

问题描述

对不起简单的问题，我是初学java和android开发者。当调用surfaceChanged时，如何在setCameraDisplayOrientation中获取Activity的实例？

Excuse me for simple question,I'm completely beginner java and android developer. How I can get the instance of Activity in setCameraDisplayOrientation when surfaceChanged is called?

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);
        ....
    }
    }
}

推荐答案

这是一种使用静态变量来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。

Here is a way to avoid memory leaks using static variable: make static weak reference to Activity instance that will be set in onCreate(Bundle) method.

1. 在您的二级课程中写下如下内容：

1. Write in your secondary class something like below:

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

然后在Activity类的onCreate（Bundle）方法中：

Then in onCreate(Bundle) method of your Activity class:

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

以这种方式使用活动实例：

Use activity instance this way:

mActivityRef.get()

这篇关于获取活动实例的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！