Android摄像头启动顺序

<span style="font-size:18px;">import java.io.IOException;import java.util.List;import android.annotation.TargetApi;import android.hardware.Camera;import android.hardware.Camera.Size;import android.os.Build;import android.os.Bundle;import android.support.v4.app.Fragment;import android.util.Log;import android.view.LayoutInflater;import android.view.SurfaceHolder;import android.view.SurfaceView;import android.view.View;import android.view.ViewGroup;import android.widget.Button;public class CrimeCameraFragment extends Fragment {private static final String TAG="CrimeCameraFragment";private Camera mCamera;private SurfaceView mSurfaceView;private Size getBestSupportedSize(List<Size> sizes,int width,int height){Size bestSize=sizes.get(0);int largestArea=bestSize.width*bestSize.height;for(Size s:sizes){int area=s.width*s.height;if(area>largestArea){bestSize=s;largestArea=area;}}return bestSize;}@SuppressWarnings("deprecation")@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup parent,Bundle savedInstanceState){<span style="color:#ff0000;">Log.d(TAG,"onCreateView() calling...");</span>View v=inflater.inflate(R.layout.fragment_crime_camera, parent,false);Button takePictureButton=(Button)v.findViewById(R.id.crime_camera_takePictureButton);takePictureButton.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubgetActivity().finish();}});mSurfaceView=(SurfaceView)v.findViewById(R.id.crime_camera_surfaceView);SurfaceHolder holder=mSurfaceView.getHolder();//setType() and SURFACE_TYPE_PUSH_BUFFERS are both deprecated//but are required for Camera preview to work on pre-3.0 devices.holder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);holder.addCallback(new SurfaceHolder.Callback() {@Overridepublic void surfaceDestroyed(SurfaceHolder holder) {// TODO Auto-generated method stubif(mCamera!=null){mCamera.stopPreview();<span style="color:#ff0000;">Log.d(TAG,"holder.surfaceDestroyed() called");</span>}}@Overridepublic void surfaceCreated(SurfaceHolder holder) {// TODO Auto-generated method stubtry{if(mCamera!=null){mCamera.setPreviewDisplay(holder);<span style="color:#ff0000;">Log.d(TAG,"holder.surfaceCreated() called");</span>}}catch(IOException e){<span style="color:#ff0000;">Log.e(TAG,"Error setting up preview display",e);</span>}}@Overridepublic void surfaceChanged(SurfaceHolder holder, int format, int width,int height) {// TODO Auto-generated method stubif(mCamera==null) {<span style="color:#ff0000;">Log.d(TAG,"calling surfaceChanged,mCamera==null");</span>return;}//The surface has changed size;update the camera preivew sizeCamera.Parameters parameters=mCamera.getParameters();//Size s=null;//To be reset in the next section//get the best supportedsizeSize s=getBestSupportedSize(parameters.getSupportedPreviewSizes(),width,height);parameters.setPreviewSize(s.width, s.height);mCamera.setParameters(parameters);try{mCamera.startPreview();<span style="color:#ff0000;">Log.d(TAG,"mCamera.startPreview() called");</span>}catch(Exception e){<span style="color:#ff0000;">Log.e(TAG,"Could not start preview",e);</span>mCamera.release();mCamera=null;}}});<span style="color:#ff0000;">Log.d(TAG,"leaving onCreateView()");</span>return v;}@TargetApi(Build.VERSION_CODES.GINGERBREAD) @Overridepublic void onResume(){super.onResume();<span style="color:#ff0000;">Log.d(TAG,"onResume() calling");</span>if(Build.VERSION.SDK_INT>=Build.VERSION_CODES.GINGERBREAD){mCamera=Camera.open(0);<span style="color:#ff0000;">Log.d(TAG,"Camera.open(0) called");</span>}else{mCamera=Camera.open();Log.d(TAG,"Camera.open() called");}}@Overridepublic void onPause(){super.onPause();if(mCamera!=null){mCamera.release();mCamera=null;<span style="color:#ff0000;">Log.d(TAG,"onPaused() called");</span>}}}</span>

启动Camera的Fragment代码如上所示，在关键处调用了Lod.d( TAG, String )函数，用以追踪代码执行流程，在Logcat中捕获的Log信息如下图：

由Logcat可以看出，在调用完 onCreateView()后，函数系统才调用onResume()函数，在onResume()函数中代开摄像头，调用了代码：

<span style="font-size:18px;">mCamera=Camera.open(0);Log.d(TAG,"Camera.open(0) called");</span>

然后才相继调用SurfaceView的Holder添加的回调函数 surfaceCreated(SurfaceHolder holder) 和 surfaceChanged(Surfaceholder holder , int format ,int width , int height)。

当从SurfaceView返回时，调用 onPause()函数，在onPause()函数中释放摄像头资源。

最后才调用了 surfaceDestroyed(SurfaceHolder holder)，而此时 mCamera资源已经被释放了。