android 图片预览切换,Android 实例实现自定义Camera和前后置摄像头切换以及图片缩小放大预览...

好的，我会尽力回答你的问题。首先，让我们来看一下如何实现自定义Camera和前后置摄像头切换。

1. 自定义Camera

首先，在AndroidManifest.xml文件中添加以下权限：

<uses-feature android:name="android.hardware.camera" />
<uses-permission android:name="android.permission.CAMERA" />

然后，在你的Activity中，创建一个Preview类，继承SurfaceView，并实现SurfaceHolder.Callback接口。

public class Preview extends SurfaceView implements SurfaceHolder.Callback {
    private SurfaceHolder mHolder;
    private Camera mCamera;

    public Preview(Context context, Camera camera) {
        super(context);
        mCamera = camera;
        mHolder = getHolder();
        mHolder.addCallback(this);
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        try {
            mCamera.setPreviewDisplay(holder);
            mCamera.startPreview();
        } catch (IOException e) {
            Log.d("Preview", "Error setting camera preview: " + e.getMessage());
        }
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        if (mHolder.getSurface() == null) {
            return;
        }
        try {
            mCamera.stopPreview();
        } catch (Exception e) {
            Log.d("Preview", "Error stopping camera preview: " + e.getMessage());
        }
        try {
            mCamera.setPreviewDisplay(mHolder);
            mCamera.startPreview();
        } catch (Exception e) {
            Log.d("Preview", "Error starting camera preview: " + e.getMessage());
        }
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        mCamera.stopPreview();
        mHolder.removeCallback(this);
    }
}

然后，在你的Activity中，创建一个Camera对象，并将其设置给Preview类。

public class CameraActivity extends Activity {
    private Camera mCamera;
    private Preview mPreview;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        mCamera = getCameraInstance();
        mPreview = new Preview(this, mCamera);
        FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
        preview.addView(mPreview);
    }

    public static Camera getCameraInstance() {
        Camera c = null;
        try {
            c = Camera.open();
        } catch (Exception e) {
            Log.d("CameraActivity", "Error opening camera: " + e.getMessage());
        }
        return c;
    }
}

2. 前后置摄像头切换

为了实现前后置摄像头的切换，你需要先判断设备是否支持前置摄像头。如果支持，你可以通过Camera.getNumberOfCameras()方法来获取设备上可用的摄像头数量。然后，你可以通过Camera.open()方法打开指定的摄像头。

public void switchCamera() {
    if (Camera.getNumberOfCameras() > 1) {
        mCamera.stopPreview();
        mCamera.release();
        mCamera = null;
        if (currentCameraId == Camera.CameraInfo.CAMERA_FACING_BACK) {
            currentCameraId = Camera.CameraInfo.CAMERA_FACING_FRONT;
        } else {
            currentCameraId = Camera.CameraInfo.CAMERA_FACING_BACK;
        }
        mCamera = Camera.open(currentCameraId);
        mPreview.setCamera(mCamera);
        try {
            mCamera.setPreviewDisplay(mHolder);
        } catch (IOException e) {
            Log.d("CameraActivity", "Error setting camera preview: " + e.getMessage());
        }
        mCamera.startPreview();
    }
}

3. 图片缩小放大预览

为了实现图片的缩小和放大预览，你可以使用Matrix类来对Bitmap进行缩放操作。

public void zoom(float scale) {
    Matrix matrix = new Matrix();
    matrix.postScale(scale, scale);
    Bitmap scaledBitmap = Bitmap.createBitmap(mBitmap, 0, 0, mBitmap.getWidth(), mBitmap.getHeight(), matrix, true);
    mImageView.setImageBitmap(scaledBitmap);
}

这样，你就可以实现自定义Camera和前后置摄像头切换以及图片缩小放大预览了。