android camera 自定义开发

1、检测是否有摄像头

　　

/** 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;
    }
}

2.3后提供了一个方法可获取摄像头的个数：Camera.getNumberOfCameras()

2、访问获取camera对象

/** 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
}

Caution: Always check for exceptions when using Camera.open(). Failing to check for exceptions if the camera is in use or does not exist will cause your application to be shut down by the system.

　　每次使用时都需要检测camera是否可用，否则很可能会让你的应用强制关闭。

　　在2.3或更高版本中，可以使用Camera.open(int)方法来请求打开哪个摄像头，如果有多前置摄像头，open(1)则是打开前置摄像头，open(0)是打开后置摄像头

3、检查摄像头的特性

　　Once you obtain access to a camera, you can get further information about its capabilities using the Camera.getParameters() method and checking the returned Camera.Parameters object for supported capabilities. When using API Level 9 or higher, use the Camera.getCameraInfo() to determine if a camera is on the front or back of the device, and the orientation of the image.

　　

4、Creating a preview class

　　为了让用户可以更好的排出自己想要的照片或视频，用户就需要知道当前摄像头获取到的图片或视频数据，这个时候就需要一个组件来展示让用户预览这些数据。SurfaceView就是这么一个可以预览摄像头当前获取到的图片或视频的组件。

　　下面的代码演示了如何创建一个基本的预览框，这个预览框可以放在任何的layout内。 这个类实现了SurfaceHolder.Callback 这个接口以用来监听预览组件的创建和销毁。

/** 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());
        }
    }
}

　　如果你想给摄像头设置一个特定大小的预览框，需要在surfaceChanged()这个方法内进行修改，当设置尺寸时需要在getSupportedPreviewSizes()的范围内，而不应该使用setPreviewSize()方法随意设置。

5、Placing preview in a layout

　　预览图必须要与其他的api共同使用才有效果，无论是拍照还是摄像的预览都需要依赖于activity进行预览展示，下面就是一个最基本的预览图的layout及activity的创建方式，在下面的示例中，FrameLayout 是摄像头预览框的容器。

<?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>

On most devices, the default orientation of the camera preview is landscape. This example layout specifies a horizontal (landscape) layout and the code below fixes the orientation of the application to landscape. For simplicity in rendering a camera preview, you should change your application's preview activity orientation to landscape by adding the following to your manifest.

　　在大部分的设备中，默认的摄像头预览方向为横屏，下面我们也就直接使用横屏的方式创建Activity

<activity android:name=".CameraActivity"
          android:label="@string/app_name"

          android:screenOrientation="landscape">
          <!-- configure this activity to use landscape orientation -->

          <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

注意：预览不是一定要用横屏，从2.2（API Level8）版本开始，你可以使用setDisplayOrientation()方法来设置预览图片的方向，为了改变预览的方向，你还需要在surfaceChanged()方法中嫌停止预览，然后更改方向后再重新启动预览。

在你的Activity中，将预览的组件加入FrameLayout中，当Activity处与pause 或者 destroy时，你需要释放Camera的资源以备其他应用使用。

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);
    }
}

6、Capturing pictures

　　当你创建好了预览组件并且将它显示在屏幕上了，你的应用就已经做好了拍照的准备了。这个时候你需要为你的程序创建Listeners来对Camera进行监控。

　　为了拍摄下图片，你需要调用Camera.takePicture()方法，这个方法有3个参数，下面是一个简单的实现方式

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());
        }
    }
};

// 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);
        }
    }
);

至此Camera的基本用法已结束。