Android multi finger gesture

Question

I am working on multi finger gestures, I tried using Google gesture builder but it will not support for multi finger gestures, How to recognize two finger V shape gesture in android.?

Answer 1

I'm sure you can use a ScaleGestureDetector for this.

After all a "V" from the top is just a pinch with some translation on the Y axis.

So I think you can analyse the focus point and scale factor to determine a "V" has taken place.

Here is a working example. In the end I didn't need to look at the scale. There are a couple of sensitivity values you can adjust such as the range of acceptable angles and the ratio of Y to X movement.

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.widget.TextView;

public class MainActivity extends Activity {

    public static class VListener extends
            ScaleGestureDetector.SimpleOnScaleGestureListener {
        private float initialFocusX;
        private float initialFocusY;

        @Override
        public boolean onScaleBegin(ScaleGestureDetector detector) {
            Log.d(TAG, String.format("%.2f,%.2f s:%.2f", detector.getFocusX(),
                    detector.getFocusY(), detector.getScaleFactor()));
            initialFocusX = detector.getFocusX();
            initialFocusY = detector.getFocusY();
            return true;
        }

        @Override
        public void onScaleEnd(ScaleGestureDetector detector) {
            float deltaX = detector.getFocusX() - initialFocusX;
            float deltaY = detector.getFocusY() - initialFocusY;

            if (deltaY == 0) {
                Log.d(TAG, "Not a V, no Y movement");
                onNonV();
                return;
            }

            float yMovementRatio = Math.abs(deltaY / deltaX);
            if (yMovementRatio < 4) {
                Log.d(TAG,
                        String.format(
                                "Not a V, the ratio of Y movement to X was not high enough: %.2f",
                                yMovementRatio));
                onNonV();
                return;
            }

            float angle = (float) Math.toDegrees(Math.atan2(deltaY, deltaX));
            if (angle > 80 && angle < 100) {
                Log.d(TAG, "V!");
                onV();
                return;
            } else {
                Log.d(TAG,
                        String.format(
                                "Not a V, the angle shows the V was drawn in the wrong direction: %.2f",
                                angle));
                onNonV();
            }
        }

        protected void onV() {
        }

        protected void onNonV() {
        }
    }

    protected static final String TAG = "MainActivity";

    private ScaleGestureDetector mScaleGestureDetector;

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

        final TextView t = (TextView) findViewById(R.id.vTextIndicator);

        mScaleGestureDetector = new ScaleGestureDetector(this, new VListener() {
            @Override
            protected void onV() {
                t.setText("V!");
            }

            @Override
            protected void onNonV() {
                t.setText("Non V");
            }
        });
    }

    public boolean onTouchEvent(MotionEvent event) {
        boolean retVal = mScaleGestureDetector.onTouchEvent(event);
        return retVal || super.onTouchEvent(event);
    }

}

activity_main.xml Layout is just:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <TextView
        android:id="@+id/vTextIndicator"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true" />

</RelativeLayout>