Detect single touch on custom View

In this exercise, we are going to create a custom view, SingleTouchView. With onTouchEvent() overrided to handle single touch event.







SingleTouchView.java

package com.exercise.AndroidTouch;

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 SingleTouchView extends View {
 private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
 private float x, y;
 private boolean touching = false;

 public SingleTouchView(Context context) {
  super(context);
  // TODO Auto-generated constructor stub
 }

 public SingleTouchView(Context context, AttributeSet attrs) {
  super(context, attrs);
  // TODO Auto-generated constructor stub
 }

 public SingleTouchView(Context context, AttributeSet attrs, int defStyle) {
  super(context, attrs, defStyle);
  // TODO Auto-generated constructor stub
 }

 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  // TODO Auto-generated method stub
  setMeasuredDimension(MeasureSpec.getSize(widthMeasureSpec),
           MeasureSpec.getSize(heightMeasureSpec));
 }

 @Override
 protected void onDraw(Canvas canvas) {
  // TODO Auto-generated method stub
  super.onDraw(canvas);
  
  if(touching){
   paint.setStrokeWidth(1);
      paint.setColor(Color.WHITE);
      paint.setStyle(Paint.Style.FILL);
      canvas.drawCircle(x, y, 75f, paint);
  }

 }

 @Override
 public boolean onTouchEvent(MotionEvent motionEvent) {
  // TODO Auto-generated method stub
  
  switch(motionEvent.getAction()){
  case MotionEvent.ACTION_MOVE:
  case MotionEvent.ACTION_DOWN:
   x = motionEvent.getX();
      y = motionEvent.getY();
      touching = true;
      break;
  default:
   touching = false;
  }
  invalidate();
  return true;
 }

}

Modify main.xml to include SingleTouchView

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<com.exercise.AndroidTouch.SingleTouchView  
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" 
    />
</LinearLayout>

Do nothing on the main activity code, AndroidTouch.java

package com.exercise.AndroidTouch;

import android.app.Activity;
import android.os.Bundle;

public class AndroidTouch extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }
}

Download the files.


Related Article:
- Detect Multi touch on custom View