Android自动对焦回调

Question

我正在使用检测相机是否成功进行自动对焦的项目。每次相机在对象中自动对焦时，我想调用一个函数（Toast）。我使用下面的代码但它只在第一次尝试时起作用。当我尝试再次聚焦凸轮时，不会调用该功能。

CameraView.java

package com.example.xx.myapplication;

import android.content.Context;
import android.hardware.Camera;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.widget.Toast;
import android.hardware.Camera.AutoFocusCallback;

import java.io.IOException;

public class CameraView extends SurfaceView implements SurfaceHolder.Callback{
    private SurfaceHolder mHolder;
    private Camera mCamera;
    public CameraView(Context context, Camera camera){
        super(context);

        mCamera = camera;
        mCamera.setDisplayOrientation(90);
        //get the holder and set this class as the callback, so we can get camera data here
        mHolder = getHolder();
        mHolder.addCallback(this);
        mHolder.setType(SurfaceHolder.SURFACE_TYPE_NORMAL);
    }

    @Override
    public void surfaceCreated(SurfaceHolder surfaceHolder) {
        try{
            //when the surface is created, we can set the camera to draw images in this surfaceholder
            mCamera.setPreviewDisplay(surfaceHolder);
            mCamera.startPreview();

            mCamera.autoFocus(new AutoFocusCallback() {
                public void onAutoFocus(boolean success, Camera camera) {
                    Toast.makeText(getContext(), "This is my Toast message!", Toast.LENGTH_LONG).show();
                }
            });
        } catch (IOException e) {
            Log.d("ERROR", "Camera error on surfaceCreated " + e.getMessage());
        }
    }

    @Override
    public void surfaceChanged(SurfaceHolder surfaceHolder, int i, int i2, int i3) {
        //before changing the application orientation, you need to stop the preview, rotate and then start it again
        if(mHolder.getSurface() == null)//check if the surface is ready to receive camera data
            return;

        try{
            mCamera.stopPreview();
        } catch (Exception e){
            //this will happen when you are trying the camera if it's not running
        }

        //now, recreate the camera preview
        try{
            mCamera.setPreviewDisplay(mHolder);
            mCamera.startPreview();



            mCamera.autoFocus(new AutoFocusCallback() {
                public void onAutoFocus(boolean success, Camera camera) {
                    Toast.makeText(getContext(), "This is my Toast message!", Toast.LENGTH_LONG).show();
                }
            });
        } catch (IOException e) {
            Log.d("ERROR", "Camera error on surfaceChanged " + e.getMessage());
        }
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder surfaceHolder) {
        //our app has only one screen, so we'll destroy the camera in the surface
        //if you are unsing with more screens, please move this code your activity
        mCamera.stopPreview();
        mCamera.release();
    }
}

MainActivity.java

package com.example.xxx.myapplication;

import android.hardware.Camera;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.FrameLayout;
import android.widget.ImageButton;
import android.widget.Toast;

import static java.security.AccessController.getContext;

public class MainActivity extends AppCompatActivity {
    private Camera mCamera = null;
    private CameraView mCameraView = null;
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        try {
            mCamera = Camera.open();//you can use open(int) to use different cameras
            Camera.Parameters params = mCamera.getParameters();
//*EDIT*//params.setFocusMode("continuous-picture");
            params.setFocusMode(Camera.Parameters.FOCUS_MODE_CONTINUOUS_PICTURE);
            mCamera.setParameters(params);

            mCamera.autoFocus(new Camera.AutoFocusCallback() {
                public void onAutoFocus(boolean success, Camera camera) {
                    Toast.makeText(getApplicationContext(), "This is my Toast message!", Toast.LENGTH_LONG).show();
                }
            });
        } catch (Exception e){
            Log.d("ERROR", "Failed to get camera: " + e.getMessage());
        }

        if(mCamera != null) {
            mCameraView = new CameraView(this, mCamera);//create a SurfaceView to show camera data
            FrameLayout camera_view = (FrameLayout)findViewById(R.id.camera_view);
            camera_view.addView(mCameraView);//add the SurfaceView to the layout
        }
    }
}

代码有什么问题？