android Camera使用示例

以下是一个简单的 Android Camera 使用示例：

1. 首先，在 AndroidManifest.xml 文件中添加相机的权限：

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

2. 在布局文件中添加一个 SurfaceView 作为相机的预览视图：

<SurfaceView
    android:id="@+id/camera_preview"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

3. 在 Activity 中获取相机实例并设置预览视图：

private Camera mCamera;
private SurfaceView mPreview;

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

    mPreview = (SurfaceView) findViewById(R.id.camera_preview);

    // 获取相机实例
    mCamera = getCameraInstance();

    // 设置预览视图
    CameraPreview cameraPreview = new CameraPreview(this, mCamera);
    mPreview.addView(cameraPreview);
}

// 获取相机实例的方法
private Camera getCameraInstance() {
    Camera camera = null;
    try {
        camera = Camera.open();
    } catch (Exception e) {
        // 相机不可用或无法访问
    }
    return camera;
}

4. 创建一个 CameraPreview 类，继承 SurfaceView 并实现 SurfaceHolder.Callback 接口：

public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {

    private SurfaceHolder mHolder;
    private Camera mCamera;

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

        // 初始化 SurfaceHolder，并添加回调
        mHolder = getHolder();
        mHolder.addCallback(this);
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        // 当 Surface 创建时，启动相机预览
        try {
            mCamera.setPreviewDisplay(holder);
            mCamera.startPreview();
        } catch (IOException e) {
            // 相机预览失败
        }
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        // 当 Surface 改变时，调整相机预览大小
        if (mHolder.getSurface() == null || mCamera == null) {
            return;
        }

        try {
            mCamera.stopPreview();
        } catch (Exception e) {
            // 忽略异常
        }

        try {
            Camera.Parameters parameters = mCamera.getParameters();
            List<Camera.Size> sizes = parameters.getSupportedPreviewSizes();
            Camera.Size optimalSize = getOptimalPreviewSize(sizes, width, height);
            parameters.setPreviewSize(optimalSize.width, optimalSize.height);
            mCamera.setParameters(parameters);
            mCamera.setPreviewDisplay(mHolder);
            mCamera.startPreview();
        } catch (Exception e) {
            // 相机预览失败
        }
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        // 当 Surface 销毁时，释放相机资源
        if (mCamera != null) {
            mCamera.stopPreview();
            mCamera.release();
            mCamera = null;
        }
    }

    // 获取最佳的相机预览尺寸
    private Camera.Size getOptimalPreviewSize(List<Camera.Size> sizes, int width, int height) {
        final double ASPECT_TOLERANCE = 0.1;
        double targetRatio = (double) width / height;

        if (sizes == null) {
            return null;
        }

        Camera.Size optimalSize = null;
        double minDiff = Double.MAX_VALUE;

        int targetHeight = height;

        for (Camera.Size size : sizes) {
            double ratio = (double) size.width / size.height;

            if (Math.abs(ratio - targetRatio) > ASPECT_TOLERANCE) {
                continue;
            }

            if (Math.abs(size.height - targetHeight) < minDiff) {
                optimalSize = size;
                minDiff = Math.abs(size.height - targetHeight);
            }
        }

        if (optimalSize == null) {
            minDiff = Double.MAX_VALUE;
            for (Camera.Size size : sizes) {
                if (Math.abs(size.height - targetHeight) < minDiff) {
                    optimalSize = size;
                    minDiff = Math.abs(size.height - targetHeight);
                }
            }
        }

        return optimalSize;
    }
}

5. 最后，在 Activity 的 onDestroy() 方法中释放相机资源：

@Override
protected void onDestroy() {
    super.onDestroy();

    if (mCamera != null) {
        mCamera.release();
        mCamera = null;
    }
}

以上是一个简单的 Android Camera 使用示例，可以实现基本的相机预览功能。