使用 Camera API 在 Android 上切换相机

Question

您好，我是 Camera API 的新手。 我正在自学！ 我只想将我的相机前后切换！ 我的设备确实有前后摄像头！ 我这样做是这样的：

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public class CameraFrag extends Fragment {

//Variables
private Camera mCamera;
private CameraPreview mPreview;
private ToggleButton flipCamera;
////////////////////////////////////

public CameraFrag() {
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    //inflate the layout
    View v = inflater.inflate(R.layout.frag, container, false);

    flipCamera = (ToggleButton) v.findViewById(R.id.flipper);

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

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

    flipCamera.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
            // TODO Auto-generated method stub
            try{
                mCamera.stopPreview();

                if(isChecked){
                    mCamera=openFrontFacingCamera();
                }
                else{
                    mCamera=openBackFacingCamera();
                }
                mCamera.startPreview();
            }catch(Exception exp){
                Log.i("#LOGTAG","EXCEPTION "+exp);
            }
        }
    });

    return v;
}

private Camera openBackFacingCamera() {
    int cameraCount = 0;
    Camera cam = null;
    Camera.CameraInfo cameraInfo = new Camera.CameraInfo();
    cameraCount = Camera.getNumberOfCameras();
    for (int camIdx = 0; camIdx < cameraCount; camIdx++) {
        Camera.getCameraInfo(camIdx, cameraInfo);
        if (cameraInfo.facing == Camera.CameraInfo.CAMERA_FACING_BACK) {
            cam = Camera.open(camIdx);
        }
    }

    return cam;
}

private Camera openFrontFacingCamera() {
    int cameraCount = 0;
    Camera cam = null;
    Camera.CameraInfo cameraInfo = new Camera.CameraInfo();
    cameraCount = Camera.getNumberOfCameras();
    for (int camIdx = 0; camIdx < cameraCount; camIdx++) {
        Camera.getCameraInfo(camIdx, cameraInfo);
        if (cameraInfo.facing == Camera.CameraInfo.CAMERA_FACING_FRONT) {
            cam = Camera.open(camIdx);
        }
    }

    return cam;
}

/** 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
}

}

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问题是它总是抛出一个异常：

I/#LOGTAG: EXCEPTION java.lang.RuntimeException: 连接相机服务失败

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如果我使用我的代码：

              try{
                mCamera.stopPreview();
                mCamera.release();
                if(isChecked){
                    mCamera=openFrontFacingCamera();
                }
                else{
                    mCamera=openBackFacingCamera();
                }
                mCamera.startPreview();
            }catch(Exception exp){
                Log.i("#LOGTAG","EXCEPTION "+exp);
            }

当我单击返回按钮时，我的预览冻结并返回！

---

我在做什么错？ 在相机之间切换是否正确？ 有人可以帮我吗？

提前致谢！

Answer 1

只需打开所需的相机，如下所示：

对于前置摄像头：

c = Camera.open(Camera.CameraInfo.CAMERA_FACING_FRONT);

对于后置摄像头：

c = Camera.open(Camera.CameraInfo.CAMERA_FACING_BACK);

并确保在完成后始终释放相机或使用以下代码释放片段的onPause方法，否则相机实例将永远不会被释放，甚至您的主相机应用程序也无法获取它。

private void releaseCameraAndPreview() {
    if (mCamera != null) {
        mCamera.stopPreview();
        mCamera.release();
        mCamera = null;
    }
}

Answer 2

对于将来面临同样问题的任何人。 当相机已经在使用时会发生错误，我通过首先释放相机然后将其设置为空并再次打开它来解决问题。

//for front camera
 camera.release();
 camera = null;
 camera =  Camera.open(Camera.CameraInfo.CAMERA_FACING_FRONT);

//for back camera
 camera.release();
 camera = null;
 camera =  Camera.open(Camera.CameraInfo.CAMERA_FACING_BACK);