android直接控制照相机硬件技术

直接控制硬件需要比使用相机应用使用更多的代码来实现。但为了实现特定的应用和将一些功能完全的集成到你的应用程序中，你必须要这么做。

1.打开相机对象。

首先需要获得Camera对象实例。就像Android自身的相机应用一样，在OnCreate()方法中，建立新的线程来代开Camera。我们经常在OnResume()方法中实现，在OnResume()方法中实现的好处是使代码可以被在次使用和简化控制流。调用Camera.open(),如果Camera已经在使用，就抛出一个异常：

private boolean safeCameraOpen(int id) {
    boolean qOpened = false;
 
    try {
        releaseCameraAndPreview();
        mCamera = Camera.open(id);
        qOpened = (mCamera != null);
    } catch (Exception e) {
        Log.e(getString(R.string.app_name), "failed to open Camera");
        e.printStackTrace();
    }

    return qOpened;   
}

private void releaseCameraAndPreview() {
    mPreview.setCamera(null);
    if (mCamera != null) {
        mCamera.release();
        mCamera = null;
    }
}

2.创建相机预览。在拍照之前，我们需要提供预览功能，这个功能由SurfaceView实现。

为了实现预览，我们需要实现android.view.SurfaceHolder.Callback接口，它是用来从相机硬件来传递图片的。

class Preview extends ViewGroup implements SurfaceHolder.Callback {

    SurfaceView mSurfaceView;
    SurfaceHolder mHolder;

    Preview(Context context) {
        super(context);

        mSurfaceView = new SurfaceView(context);
        addView(mSurfaceView);

        // Install a SurfaceHolder.Callback so we get notified when the
        // underlying surface is created and destroyed.
        mHolder = mSurfaceView.getHolder();
        mHolder.addCallback(this);
        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }
...
}

设置和开启预览。在开始预览之前，我们必须要将预览类传递给camera对象。

public void setCamera(Camera camera) {
    if (mCamera == camera) { return; }
   
    stopPreviewAndFreeCamera();
   
    mCamera = camera;
   
    if (mCamera != null) {
        List<Size> localSizes = mCamera.getParameters().getSupportedPreviewSizes();
        mSupportedPreviewSizes = localSizes;
        requestLayout();
     
        try {
            mCamera.setPreviewDisplay(mHolder);
        } catch (IOException e) {
            e.printStackTrace();
        }
     
        /*
          Important: Call startPreview() to start updating the preview surface. Preview must
          be started before you can take a picture.
          */
        mCamera.startPreview();
    }
}

修改相机设置。下面代码是预览大小的设置代码：

public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
    // Now that the size is known, set up the camera parameters and begin
    // the preview.
    Camera.Parameters parameters = mCamera.getParameters();
    parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
    requestLayout();
    mCamera.setParameters(parameters);

    /*
      Important: Call startPreview() to start updating the preview surface. Preview must be
      started before you can take a picture.
    */
    mCamera.startPreview();
}

使用setCameraDisplayOrientation()设置相机显示的方向。使用Camera.takePicture()来拍照。

重新预览：

@Override
public void onClick(View v) {
    switch(mPreviewState) {
    case K_STATE_FROZEN:
        mCamera.startPreview();
        mPreviewState = K_STATE_PREVIEW;
        break;

    default:
        mCamera.takePicture( null, rawCallback, null);
        mPreviewState = K_STATE_BUSY;
    } // switch
    shutterBtnConfig();
}

停止预览释放相机：

public void surfaceDestroyed(SurfaceHolder holder) {
    // Surface will be destroyed when we return, so stop the preview.
    if (mCamera != null) {
        /*
Call stopPreview() to stop updating the preview surface.
        */
        mCamera.stopPreview();
    }
}

/**
  * When this function returns, mCamera will be null.
  */
private void stopPreviewAndFreeCamera() {

    if (mCamera != null) {
        /*
          Call stopPreview() to stop updating the preview surface.
        */
        mCamera.stopPreview();
   
        /*
          Important: Call release() to release the camera for use by other applications.
          Applications should release the camera immediately in onPause() (and re-open() it in
          onResume()).
        */
        mCamera.release();
   
        mCamera = null;
    }
}