控制设备的照相机（camera）

一、添加权限：

使用摄像头：

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

注：如果通过意图开启设备上已有的照相app，则不需要该权限。

设备需拥有摄像头：

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

存储图像或录像到SD卡：

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

摄像是需要录音：

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

二、用Intent使用已有的照相机app：

拍照：Action：MediaStore.ACTION_IMAGE_CAPTURE ；
      Extra：MediaStore.EXTRA_OUTPUT：指定存储路径的URI。

录像：Action:MediaStore.ACTION_VIDEO_CAPTURE；
      Extra：MediaStore.EXTRA_OUTPUT：指定存储路径的URI；
             MediaStore.EXTRA_VIDEO_QUALITY：0表示最差画质，1表示最高画质；
    MediaStore.EXTRA_DURATION_LIMIT：视频拍摄的最大时长（以秒为单位）；
    MediaStore.EXTRA_SIZE_LIMIT ：视频文件的大小限制（以字节为单位）。

开启的照相机app返回的Intent中包含了表示文件存储位置的URI，可以调用getData()方法获得。


三、创建你自己的照相机：

1.检测是否有摄像头硬件：

/** 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;
    }
}

2.获取camera实例：

/** 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
}

注：Android设备可以有多个摄像头，API level 9之后允许你通过调用 Camera.getNumberOfCameras() 
方法获得可用摄像头数，也可以在open（）函数中添加参数，以获取指定的摄像头。

4.创建预览类：
当用户点击按钮拍照前，可以通过摄像头看到物体的预览，可以通过surfaceview创建一个预览类，实现SurfaceHolder.Callback 接口，如：

/** 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());
        }
    }
}

5.为预览创建一个布局，如：

<?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>

上述的FrameLayout用来加载预览，这样其他的界面组件可叠加在预览图片上。

6.将预览添加到FrameLayout中：

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);
    }
}

7. 点击按钮拍照：

（1）实现回调将图片存到指定位置：

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());
        }
    }
};

（2）点击按钮捕获图像（通过调用takePicture(）方法）：

// 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);
        }
    }
);

四、录像（使用MediaRecorder类）：

1.配置步骤：

private boolean prepareVideoRecorder(){

    mCamera = getCameraInstance();
    mMediaRecorder = new MediaRecorder();

    // Step 1: Unlock and set camera to MediaRecorder
    mCamera.unlock();
    mMediaRecorder.setCamera(mCamera);

    // Step 2: Set sources
    mMediaRecorder.setAudioSource(MediaRecorder.AudioSource.CAMCORDER);
    mMediaRecorder.setVideoSource(MediaRecorder.VideoSource.CAMERA);

    // Step 3: Set a CamcorderProfile (requires API Level 8 or higher)
    mMediaRecorder.setProfile(CamcorderProfile.get(CamcorderProfile.QUALITY_HIGH));

    // Step 4: Set output file
    mMediaRecorder.setOutputFile(getOutputMediaFile(MEDIA_TYPE_VIDEO).toString());

    // Step 5: Set the preview output
    mMediaRecorder.setPreviewDisplay(mPreview.getHolder().getSurface());

    // Step 6: Prepare configured MediaRecorder
    try {
        mMediaRecorder.prepare();
    } catch (IllegalStateException e) {
        Log.d(TAG, "IllegalStateException preparing MediaRecorder: " + e.getMessage());
        releaseMediaRecorder();
        return false;
    } catch (IOException e) {
        Log.d(TAG, "IOException preparing MediaRecorder: " + e.getMessage());
        releaseMediaRecorder();
        return false;
    }
    return true;
}

当系统版本低于2.2（API level 8）时，Step 3应替换为：

 // Step 3: Set output format and encoding (for versions prior to API Level 8)
    mMediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_4);
    mMediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.DEFAULT);
    mMediaRecorder.setVideoEncoder(MediaRecorder.VideoEncoder.DEFAULT);

可以调用以下这些方法去更改一些MediaRecorder默认的设置：

setVideoEncodingBitRate()；
setVideoSize()；
setVideoFrameRate()；
setAudioEncodingBitRate()；
setAudioChannels()；
setAudioSamplingRate()。

2.点击按钮开始录像：

private boolean isRecording = false;

// 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) {
            if (isRecording) {
                // stop recording and release camera
                mMediaRecorder.stop();  // stop the recording
                releaseMediaRecorder(); // release the MediaRecorder object
                mCamera.lock();         // take camera access back from MediaRecorder

                // inform the user that recording has stopped
                setCaptureButtonText("Capture");
                isRecording = false;
            } else {
                // initialize video camera
                if (prepareVideoRecorder()) {
                    // Camera is available and unlocked, MediaRecorder is prepared,
                    // now you can start recording
                    mMediaRecorder.start();

                    // inform the user that recording has started
                    setCaptureButtonText("Stop");
                    isRecording = true;
                } else {
                    // prepare didn't work, release the camera
                    releaseMediaRecorder();
                    // inform user
                }
            }
        }
    }
);

3.释放资源：

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 releaseMediaRecorder(){
        if (mMediaRecorder != null) {
            mMediaRecorder.reset();   // clear recorder configuration
            mMediaRecorder.release(); // release the recorder object
            mMediaRecorder = null;
            mCamera.lock();           // lock camera for later use
        }
    }

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

注：如果不释放资源，那么接下来所有尝试获取camera对象的操作都会崩溃。

4.保存捕获的文件：
用户拍摄的照片或视频应该保存在锁SD卡中，有两个标准的储存位置：
Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES)，
Context.getExternalFilesDir(Environment.DIRECTORY_PICTURES) 。

下述方法用来设置文件存储位置：

public static final int MEDIA_TYPE_IMAGE = 1;
public static final int MEDIA_TYPE_VIDEO = 2;

/** Create a file Uri for saving an image or video */
private static Uri getOutputMediaFileUri(int type){
      return Uri.fromFile(getOutputMediaFile(type));
}

/** Create a File for saving an image or video */
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 = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
    File mediaFile;
    if (type == MEDIA_TYPE_IMAGE){
        mediaFile = new File(mediaStorageDir.getPath() + File.separator +
        "IMG_"+ timeStamp + ".jpg");
    } else if(type == MEDIA_TYPE_VIDEO) {
        mediaFile = new File(mediaStorageDir.getPath() + File.separator +
        "VID_"+ timeStamp + ".mp4");
    } else {
        return null;
    }

    return mediaFile;
}

五、配置相机参数：

1.判断特性是否可用，如判断自动对焦特性：

// get Camera parameters
Camera.Parameters params = mCamera.getParameters();

List<String> focusModes = params.getSupportedFocusModes();
if (focusModes.contains(Camera.Parameters.FOCUS_MODE_AUTO)) {
  // Autofocus mode is supported
}

2.设置参数，如设置自动对焦：

// get Camera parameters
Camera.Parameters params = mCamera.getParameters();
// set the focus mode
params.setFocusMode(Camera.Parameters.FOCUS_MODE_AUTO);
// set Camera parameters
mCamera.setParameters(params);