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;

}

}