SliderListener.java

package com.example.archenemy.simplealarm;

import android.graphics.PointF;
import android.view.MotionEvent;
import android.view.View;

/**
 * Created by archenemy on 10/1/16.
 */
// http://stackoverflow.com/questions/16557076/how-to-smoothly-move-a-image-view-with-users-finger-on-android-emulator
public class SliderListener implements View.OnTouchListener{
    private View left;
    private View right;
    private View slider;
    private PointF reference;
    private OnSliderOptionSelectedListener listener;

    private PointF touchDown = new PointF();
    private PointF touchStart = new PointF();
    //------------------------------------------------------------------------------------------
    public SliderListener(View left, View slider, PointF reference, View right,
                          OnSliderOptionSelectedListener listener){
        this.left = left;
        this.reference = reference;
        this.right = right;
        this.slider = slider;
        this.listener = listener;
    }
    //------------------------------------------------------------------------------------------
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        switch( event.getAction() ){
            case MotionEvent.ACTION_MOVE:
                PointF mv = new PointF( event.getX()-touchDown.x, event.getY()-touchDown.y );
                float newX = touchStart.x + mv.x;
                if( newX < left.getX() ){
                    v.setX( left.getX() );
                    touchStart = new PointF( v.getX(),v.getY() );
                }else if( newX > right.getX() ){
                    v.setX( right.getX() );
                    touchStart = new PointF( v.getX(),v.getY() );
                }else{
                    v.setX( newX );
                    touchStart = new PointF( v.getX(),v.getY() );
                }
                break;
            case MotionEvent.ACTION_DOWN:
                touchDown.x = event.getX();
                touchDown.y = event.getY();
                touchStart = new PointF( v.getX(),v.getY() );
                break;
            case MotionEvent.ACTION_UP:
                int sliderCenterX = (int) (slider.getX() + (slider.getWidth()/2));
                int sliderCenterY = (int) (slider.getY() + (slider.getHeight()/2));
                if( isWithinBounds(sliderCenterX,sliderCenterY,left) ){
                    listener.onLeftSelected();
                }else if( isWithinBounds(sliderCenterX,sliderCenterY,right) ){
                    listener.onRightSelected();
                }else{
                    v.animate().translationX(reference.x).setDuration(250).start();
                }
                break;
            default:
                break;
        }
        return true;
    }
    //------------------------------------------------------------------------------------------
    private boolean isWithinBounds(float x,float y,View v){
        float viewX = v.getX();
        float viewY = v.getY();
        boolean isWithinBounds = true;

        isWithinBounds &= (x >= viewX && x <= viewX + v.getWidth());
        isWithinBounds &= (y >= viewY && y <= viewY + v.getHeight());

        return isWithinBounds;
    }
    //------------------------------------------------------------------------------------------
    interface OnSliderOptionSelectedListener{
        void onLeftSelected();
        void onRightSelected();
    }
}