how to draw rectange on camera preview in android

问题:

Actually I don't understand how to implement the rectangle on the camera preview. Everything working well, but I don't know the way to put the rectangle border like this link. Please anyone help me. Thanks.

回答1:

I suggest you implement your camera preview in a custom SurfaceView and then in your XML you can simply overlay the rectangle, like the accepted answer here:

Android: Overlay on Android Camera Preview

So add a Java file to your project:

public class CapturePreview extends SurfaceView implements SurfaceHolder.Callback{

    public static Bitmap mBitmap;
    SurfaceHolder holder;
    static Camera mCamera;

    public CapturePreview(Context context, AttributeSet attrs) {
    super(context, attrs);

        holder = getHolder();
        holder.addCallback(this);
        holder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width,int height) {

        Camera.Parameters parameters = mCamera.getParameters();
        parameters.getSupportedPreviewSizes();
        mCamera.setParameters(parameters);
        mCamera.startPreview();
    }
    @Override
    public void surfaceCreated(SurfaceHolder holder) {

        try {
            mCamera = Camera.open();
            mCamera.setPreviewDisplay(holder);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        mCamera.stopPreview();
        mCamera.release();
    }

    public static void takeAPicture(){  

        Camera.PictureCallback mPictureCallback = new PictureCallback() {
            @Override
            public void onPictureTaken(byte[] data, Camera camera) {

                BitmapFactory.Options options = new BitmapFactory.Options();
                mBitmap = BitmapFactory.decodeByteArray(data, 0, data.length, options);
            }
        };
        mCamera.takePicture(null, null, mPictureCallback);
    }
}

Please note you will have to make sure it has the appropriate package name.

Then change your main XML file:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical"
  android:layout_width="match_parent"
  android:layout_height="match_parent">

  <[PACKAGE_NAME].CapturePreview 
      android:layout_width="match_parent"
      android:layout_height="match_parent"/>


  <LinearLayout 
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:background:"#55999999"
      android:padding:"30dp"
      android:gravity="center">

  </LinearLayout>  

</RelativeLayout>

This should have a transparent rectangle over the camera preview.