Detect multi-touch (for 10 pointers)

It's a example to detect multi-touch on screen. Logically it can detect 10 pointers.



Implement the custom view to detect multi-touch, by overriding onTouchEvent().

package com.exercise.AndroidMultiTouch;

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 MultiToucnView extends View {
 
 private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
 
 final int MAX_NUMBER_OF_POINT = 10;
 float[] x = new float[MAX_NUMBER_OF_POINT];
 float[] y = new float[MAX_NUMBER_OF_POINT];
 boolean[] touching = new boolean[MAX_NUMBER_OF_POINT];

 public MultiToucnView(Context context, AttributeSet attrs, int defStyle) {
  super(context, attrs, defStyle);
  init();
 }

 public MultiToucnView(Context context, AttributeSet attrs) {
  super(context, attrs);
  init();
 }

 public MultiToucnView(Context context) {
  super(context);
  init();
 }

 void init() {
  paint.setStyle(Paint.Style.STROKE);
  paint.setStrokeWidth(1);
  paint.setColor(Color.WHITE);
 }

 @Override
 protected void onDraw(Canvas canvas) {
  
  for(int i = 0; i < MAX_NUMBER_OF_POINT; i++){
   if(touching[i]){
    canvas.drawCircle(x[i], y[i], 50f, paint);
   }
  }
 }

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

 @Override
 public boolean onTouchEvent(MotionEvent event) {
  int action = (event.getAction() & MotionEvent.ACTION_MASK);
  int pointCount = event.getPointerCount();
  
  for (int i = 0; i < pointCount; i++) {
    int id = event.getPointerId(i);
    
    //Ignore pointer higher than our max.
    if(id < MAX_NUMBER_OF_POINT){
     x[id] = (int)event.getX(i);
     y[id] = (int)event.getY(i);
     
     if((action == MotionEvent.ACTION_DOWN)
       ||(action == MotionEvent.ACTION_POINTER_DOWN)
       ||(action == MotionEvent.ACTION_MOVE)){
      touching[id] = true;
     }else{
      touching[id] = false;
     }
    } 
   }

  invalidate(); 
  return true;
  
 }

}

Modify main.xml to include the custom view, com.exercise.AndroidMultiTouch.MultiToucnView.

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

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/hello" />
    <com.exercise.AndroidMultiTouch.MultiToucnView
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" />
</LinearLayout>

Download the files.