写一个CameraHelper.setFrameCallback用AppCompatImageView显示摄像头实时图像的例子

好的，以下是一个简单的示例：

public class CameraPreviewActivity extends AppCompatActivity {
    
    private static final int CAMERA_PERMISSION_REQUEST_CODE = 100;
    
    private Camera camera;
    private CameraPreview cameraPreview;
    private AppCompatImageView imageView;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_camera_preview);
        
        imageView = findViewById(R.id.imageView);
        
        if (checkSelfPermission(Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
            requestPermissions(new String[]{Manifest.permission.CAMERA}, CAMERA_PERMISSION_REQUEST_CODE);
        } else {
            startCameraPreview();
        }
    }
    
    private void startCameraPreview() {
        camera = Camera.open();
        cameraPreview = new CameraPreview(this, camera);
        FrameLayout previewLayout = findViewById(R.id.cameraPreviewLayout);
        previewLayout.addView(cameraPreview);
        
        camera.setPreviewCallback(new Camera.PreviewCallback() {
            @Override
            public void onPreviewFrame(byte[] data, Camera camera) {
                Bitmap bitmap = getBitmapFromCameraData(data, camera);
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        imageView.setImageBitmap(bitmap);
                    }
                });
            }
        });
    }
    
    private Bitmap getBitmapFromCameraData(byte[] data, Camera camera) {
        Camera.Size size = camera.getParameters().getPreviewSize();
        YuvImage image = new YuvImage(data, ImageFormat.NV21, size.width, size.height, null);
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        image.compressToJpeg(new Rect(0, 0, size.width, size.height), 100, outputStream);
        byte[] jpegData = outputStream.toByteArray();
        return BitmapFactory.decodeByteArray(jpegData, 0, jpegData.length);
    }
    
    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if (requestCode == CAMERA_PERMISSION_REQUEST_CODE) {
            if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                startCameraPreview();
            } else {
                Toast.makeText(this, "Camera permission denied", Toast.LENGTH_SHORT).show();
                finish();
            }
        }
    }
    
    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (camera != null) {
            camera.stopPreview();
            camera.release();
        }
    }
}

在这个例子中，我们使用了一个 `CameraPreview` 自定义 View 来显示相机预览，它的代码如下：

public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
    
    private Camera camera;
    private SurfaceHolder holder;
    
    public CameraPreview(Context context, Camera camera) {
        super(context);
        this.camera = camera;
        this.holder = getHolder();
        this.holder.addCallback(this);
    }
    
    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        try {
            camera.setPreviewDisplay(holder);
            camera.startPreview();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    
    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        Camera.Parameters parameters = camera.getParameters();
        Camera.Size size = getBestPreviewSize(width, height, parameters);
        parameters.setPreviewSize(size.width, size.height);
        camera.setParameters(parameters);
        camera.startPreview();
    }
    
    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        camera.stopPreview();
    }
    
    private Camera.Size getBestPreviewSize(int width, int height, Camera.Parameters parameters) {
        Camera.Size result = null;
        for (Camera.Size size : parameters.getSupportedPreviewSizes()) {
            if (size.width <= width && size.height <= height) {
                if (result == null) {
                    result = size;
                } else {
                    int resultArea = result.width * result.height;
                    int newArea = size.width * size.height;
                    if (newArea > resultArea) {
                        result = size;
                    }
                }
            }
        }
        return result;
    }
}

`CameraPreview` 显示相机预览，并且在每次预览帧数据可用时，将数据转换为 Bitmap 并设置到 ImageView 中。

需要注意的是，这个例子中的代码比较简单，没有做一些必要的错误处理和异常处理，实际开发中需要根据具体情况进行调整。