Android学习十---Android Camera

Android camera用来拍照和拍摄视频的先看一下最后实现的效果图

            最后的效果图

一、准备

在你的应用程序上使用android拍照设备，需要考虑以下几个方面

1. 是否是一定需要camera

如果需要，那么就无法安装在没有摄像头的设备。

需要在mainfest 中声明

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

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

2. 是想用怎样的方式来使用相机

可以有两种方式

2.1 简单的拍照 使用已经存在camera apps 

2.2 需要更多定制的功能，创建一个camera app

3. 存储方式

是只能在本应用程序里使用还是可以被其他程序使用。

二、相关类

android.hardware.camera2

包中包含控制设备相机的基本类

Camera

过时不用的相机控制类

SurfaceView

提供实时的相机预览

MediaRecorder 

用来记录video

Intent

使用

MediaStore.ACTION_IMAGE_CAPTURE

MediaStore.ACTION_VIDEO_CAPTURE

两个Intent类型来捕获图像和视频

三、Manifest声明

camera许可

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

camera特征

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

存储许可

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

音视频录制

<uses-permission android:name="android.permission.RECORD_AUDIO" />

位置许可

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

四、使用已经存在的camera apps

使用方式是用Intent，使用Intent能够使用最少的代码来获取图片

流程主要是

创建一个camera Intent，Intent的类型包括，MediaStore.ACTION_IMAGE_CAPTURE，MediaStore.ACTION_VIDEO_CAPTURE启动一个camera Intent，使用startActivityForResult()方法来执行一个camera intent，在启动Intent后，camera应用界面能够显示在设备屏幕来供使用

接受Intent的结果，使用onActivityResult()方法来接受Intent的回调和数据。当用户结束拍照后，系统调用这一方法。

下列代码显示如何创建一个camera intent并执行

private static final int CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE = 100;
private Uri fileUri;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    // create Intent to take a picture and return control to the calling application
    Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);

    fileUri = getOutputMediaFileUri(MEDIA_TYPE_IMAGE); // create a file to save the image
    intent.putExtra(MediaStore.EXTRA_OUTPUT, fileUri); // set the image file name

    // start the image capture Intent
    startActivityForResult(intent, CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE);
}

接收camera intent的结果,主要是重载onActivityResult。

private static final int CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE = 100;
private static final int CAPTURE_VIDEO_ACTIVITY_REQUEST_CODE = 200;

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode == CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE) {
        if (resultCode == RESULT_OK) {
            // Image captured and saved to fileUri specified in the Intent
            Toast.makeText(this, "Image saved to:\n" +
                     data.getData(), Toast.LENGTH_LONG).show();
        } else if (resultCode == RESULT_CANCELED) {
            // User cancelled the image capture
        } else {
            // Image capture failed, advise user
        }
    }
}

！一但程序接受到一个成功的结果，那么应用程序就可以获取在指定路径下的图片。

五、创建一个Camera App

官方建议使用新的android.hardware.camera2，使用旧的Camera API会出现deprecated的警告。

一般创建一个定制Camera接口的步骤包括

1.检测和获取camera

/** Check if this device has a camera */
private boolean checkCameraHardware(Context context) {
    if (context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA)){
        // this device has a camera
        return true;
    } else {
        // no camera on this device
        return false;
    }
}

/** A safe way to get an instance of the Camera object. */
public static Camera getCameraInstance(){
    Camera c = null;
    try {
        c = Camera.open(); // attempt to get a Camera instance
    }
    catch (Exception e){
        // Camera is not available (in use or does not exist)
    }
    return c; // returns null if camera is unavailable
}

2.创建一个预览类

/** A basic Camera preview class */
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
    private SurfaceHolder mHolder;
    private Camera mCamera;

    public CameraPreview(Context context, Camera camera) {
        super(context);
        mCamera = camera;

        // Install a SurfaceHolder.Callback so we get notified when the
        // underlying surface is created and destroyed.
        mHolder = getHolder();
        mHolder.addCallback(this);
        // deprecated setting, but required on Android versions prior to 3.0
        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }

    public void surfaceCreated(SurfaceHolder holder) {
        // The Surface has been created, now tell the camera where to draw the preview.
        try {
            mCamera.setPreviewDisplay(holder);
            mCamera.startPreview();
        } catch (IOException e) {
            Log.d(TAG, "Error setting camera preview: " + e.getMessage());
        }
    }

    public void surfaceDestroyed(SurfaceHolder holder) {
        // empty. Take care of releasing the Camera preview in your activity.
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        // If your preview can change or rotate, take care of those events here.
        // Make sure to stop the preview before resizing or reformatting it.

        if (mHolder.getSurface() == null){
          // preview surface does not exist
          return;
        }

        // stop preview before making changes
        try {
            mCamera.stopPreview();
        } catch (Exception e){
          // ignore: tried to stop a non-existent preview
        }

        // set preview size and make any resize, rotate or
        // reformatting changes here

        // start preview with new settings
        try {
            mCamera.setPreviewDisplay(mHolder);
            mCamera.startPreview();

        } catch (Exception e){
            Log.d(TAG, "Error starting camera preview: " + e.getMessage());
        }
    }
}

3.创建一个预览的布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
  <FrameLayout
    android:id="@+id/camera_preview"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_weight="1"
    />

  <Button
    android:id="@+id/button_capture"
    android:text="Capture"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    />
</LinearLayout>

public class CameraActivity extends Activity {

    private Camera mCamera;
    private CameraPreview mPreview;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        // Create an instance of Camera
        mCamera = getCameraInstance();

        // Create our Preview view and set it as the content of our activity.
        mPreview = new CameraPreview(this, mCamera);
        FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
        preview.addView(mPreview);
    }
}

4.开始监听捕获事件

private PictureCallback mPicture = new PictureCallback() {

    @Override
    public void onPictureTaken(byte[] data, Camera camera) {

        File pictureFile = getOutputMediaFile(MEDIA_TYPE_IMAGE);
        if (pictureFile == null){
            Log.d(TAG, "Error creating media file, check storage permissions: " +
                e.getMessage());
            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());
        }
    }
};

5.捕获并保存文件

// Add a listener to the Capture button
Button captureButton = (Button) findViewById(id.button_capture);
captureButton.setOnClickListener(
    new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // get an image from the camera
            mCamera.takePicture(null, null, mPicture);
        }
    }
);

保存图片到SD卡中

private PictureCallback mPicture = new PictureCallback() {

        /** Create a File for saving an image or video */

        @Override
        public void onPictureTaken(byte[] data, Camera camera) {

            File pictureFile = getOutputMediaFile();
            if (pictureFile == null) {
                Log.d(TAG,"Error creating media file, check storage permissions: ");
                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();

        }

    };

    private File getOutputMediaFile() {
        // 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
        File mediaFile;
        String timeStamp = String.format("%d.jpg", System.currentTimeMillis());
        mediaFile = new File(mediaStorageDir.getPath() + File.separator
                + "IMG_" + timeStamp + ".jpg");
        return mediaFile;
    }

6.释放相机

public class CameraActivity extends Activity {
    private Camera mCamera;
    private SurfaceView mPreview;
    private MediaRecorder mMediaRecorder;

    ...

    @Override
    protected void onPause() {
        super.onPause();
        releaseMediaRecorder();       // if you are using MediaRecorder, release it first
        releaseCamera();              // release the camera immediately on pause event
    }

    private void releaseCamera(){
        if (mCamera != null){
            mCamera.release();        // release the camera for other applications
            mCamera = null;
        }
    }
}

caution：

相机是一个共享资源，所以每次使用完毕后要记得调用Camera.release()来释放，否则后续想要获取相机的应用都会被关闭。

六、注意问题

6.1 拍完成照片后，停在拍照完成的界面，无法继续拍摄

在onPictureTaken的实现最后添加一个启动预览camera.startPreview();

private PictureCallback mPicture = new PictureCallback() {

        /** Create a File for saving an image or video */

        @Override
        public void onPictureTaken(byte[] data, Camera camera) {

            File pictureFile = getOutputMediaFile();
            if (pictureFile == null) {
                Log.d(TAG,"Error creating media file, check storage permissions: ");
                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();

        }

    };

代码：

https://github.com/dawnminghuang/android_camera

参考资料

http://developer.android.com/guide/topics/media/camera.html