import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class Dot extends View {
    private static final float RADIUS = 20;
    private float x = 30;
    private float y = 30;
    private float initialX;
    private float initialY;
    private float offsetX;
    private float offsetY;
    private Paint backgroundPaint;
    private Paint myPaint;
    
    public Dot(Context context, AttributeSet attrs) {
        super(context, attrs);

        backgroundPaint = new Paint();
        backgroundPaint.setColor(Color.BLUE);

        myPaint = new Paint();
        myPaint.setColor(Color.WHITE);
        myPaint.setAntiAlias(true);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int action = event.getAction();
        switch(action) {
        case MotionEvent.ACTION_DOWN:
            // Need to remember where the initial starting point
            // center is of our Dot and where our touch starts from
            initialX = x;
            initialY = y;
            offsetX = event.getX();
            offsetY = event.getY();
            break;
        case MotionEvent.ACTION_MOVE:
        case MotionEvent.ACTION_UP:
        case MotionEvent.ACTION_CANCEL:
            x = initialX + event.getX() - offsetX;
            y = initialY + event.getY() - offsetY;
            break;
        }
        event.recycle();
        return(true);
    }

    @Override
    public void draw(Canvas canvas) {
        int width = canvas.getWidth();
        int height = canvas.getHeight();
        canvas.drawRect(0, 0, width, height, backgroundPaint);

        canvas.drawCircle(x, y, RADIUS, myPaint);
        invalidate();
    }
}