安卓学习历程-第四天

学习AsyncTask运行机制

           mWorker设置优先级

           将mWorker传给mFuture，调用call()->调用doInBackground()

           三个参数；

                  1.doInBackground的参数类型

                  2.任务进度类型（任务运行进度百分比）

                  3.doInBackground的返回值类型，以及onPostExecute参数类型，doInBackground的返回值传给onPostExecute

阅读camera文档

          使用api运行相机，

              程序流程：

                          编写preview类，用于预览相机图像

                                     继承SurfaceView类，重载surfaceCreated(将预览放入holder)  surfaceChanged(打开相机，启动预览)  surfaceDestroyed(释放相机)函数

                         拍照调用takePicture函数    第三个参数PictureCallback
mPicture用于处理照片相关处理(储存)

          预览类

public class MySurfaceView extends SurfaceView implements
SurfaceHolder.Callback {
private static final String TAG = "MySurfaceView";

private static SurfaceHolder holder;
private Camera mCamera;

public MySurfaceView(Context context, AttributeSet attrs) {
super(context, attrs);
Log.i(TAG, "new View ...");

holder = getHolder();//
holder.addCallback(this);
}

@Override
public void surfaceCreated(SurfaceHolder arg0) {
Log.i(TAG, "surfaceCreated...");
if (mCamera == null) {
mCamera = Camera.open();//开启相机，可以放参数 0 或 1，分别代表前置、后置摄像头，默认为 0
try {
mCamera.setPreviewDisplay(holder);//整个程序的核心，相机预览的内容放在 holder
} catch (IOException e) {
e.printStackTrace();
}
}
}

@Override
public void surfaceChanged(SurfaceHolder arg0, int arg1, int arg2, int arg3) {
Log.i(TAG, "surfaceChanged...");
mCamera.startPreview();
}

@Override
public void surfaceDestroyed(SurfaceHolder arg0) {
Log.i(TAG, "surfaceChanged...");
if (mCamera != null) {
mCamera.release();//释放相机资源
mCamera = null;
}
}

public void mtakePicture(){
mCamera.takePicture(null,null,mPicture) ;
}

private Camera.PictureCallback mPicture = new Camera.PictureCallback() {
public static final int MEDIA_TYPE_IMAGE = 1;
@Override
public void onPictureTaken(byte[] data, Camera camera) {

File pictureFile = getOutputMediaFile(MEDIA_TYPE_IMAGE);
if (pictureFile == null){
return;
}

try {
FileOutputStream fos = new FileOutputStream(pictureFile);
fos.write(data);
fos.close();
} catch (FileNotFoundException e) {
Log.d(TAG, "File not found: " + e.getMessage());
} catch (IOException e) {
Log.d(TAG, "Error accessing file: " + e.getMessage());
}
camera.startPreview();        //拍照完成后，要继续打开预览，否则会卡住，因为拍照会停止预览
}
};

private static File getOutputMediaFile(int type){
// To be safe, you should check that the SDCard is mounted
// using Environment.getExternalStorageState() before doing this.

File mediaStorageDir = new File(Environment.getExternalStoragePublicDirectory(
Environment.DIRECTORY_PICTURES), "MyCameraApp");
// This location works best if you want the created images to be shared
// between applications and persist after your app has been uninstalled.

// Create the storage directory if it does not exist
if (! mediaStorageDir.exists()){
if (! mediaStorageDir.mkdirs()){
Log.d("MyCameraApp", "failed to create directory");
return null;
}
}

// Create a media file name
String timeStamp = "test";
File mediaFile;
mediaFile = new File(mediaStorageDir.getPath() + File.separator +
"IMG_"+ timeStamp + ".jpg");
return mediaFile;
}

}

MainActivity

拍照不需要使用线程，在onClick函数中直接调用函数就好，就当作学习了

private static final String TAG = "MainActivity";
private MySurfaceView mView;
private Camera mCamera;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.activity_main);

Button button=(Button)findViewById(R.id.btn);
mView = (MySurfaceView) findViewById(R.id.mView);

button.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v){
Thread thread=new TakePicThread(mView);
thread.start();
}
});
}

public class TakePicThread extends Thread {

private MySurfaceView view;
//继承Thread类，并改写其run方法
private final static String TAG = "My Thread ===> ";

public TakePicThread(MySurfaceView v){
view=v;
}

public void run(){
Log.d(TAG, "run");
view.mtakePicture();
}
}

代码摘自：http://blog.csdn.net/kintai/article/details/48597441

                https://developer.android.google.cn/guide/topics/media/camera.html