Detect Multi-Touch Event

It's a testing app for multi-touch event, target API level 8, Android 2.2. In my test on Nexus One running 2.2.1, only two points can be recognized.

package com.TestMultiTouch;

import android.app.Activity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.widget.LinearLayout;
import android.widget.TextView;

public class TestMultiTouch extends Activity {
 
 //In this test, handle maximum of 2 pointer
 final int MAX_POINT_CNT = 2;
 
 String[] pointerAction = new String[MAX_POINT_CNT];
 float[] x = new float[MAX_POINT_CNT];
 float[] y = new float[MAX_POINT_CNT];
 TextView currentPointer;
 TextView pointerStatus_01, pointerStatus_02;
 TextView textDistance;
 
   /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.main);
       LinearLayout MainLayout = (LinearLayout)findViewById(R.id.mainlayout);
       MainLayout.setOnTouchListener(OnTouchListener);
      
       currentPointer = (TextView)findViewById(R.id.currentpointer);
       pointerStatus_01 = (TextView)findViewById(R.id.pointstatus_01);
       pointerStatus_02 = (TextView)findViewById(R.id.pointstatus_02);
       textDistance = (TextView)findViewById(R.id.distance);
   }

   private View.OnTouchListener OnTouchListener
   = new View.OnTouchListener(){

  @Override
  public boolean onTouch(View view, MotionEvent motionEvent) {
   // TODO Auto-generated method stub
   
   int pointerIndex = ((motionEvent.getAction() & MotionEvent.ACTION_POINTER_ID_MASK)
     >> MotionEvent.ACTION_POINTER_ID_SHIFT);
   int pointerId = motionEvent.getPointerId(pointerIndex);
   int action = (motionEvent.getAction() & MotionEvent.ACTION_MASK);
   int pointCnt = motionEvent.getPointerCount();
   
   if (pointCnt <= MAX_POINT_CNT){
    if (pointerIndex <= MAX_POINT_CNT - 1){

     for (int i = 0; i < pointCnt; i++) {
      int id = motionEvent.getPointerId(i);
      x[id] = (int)motionEvent.getX(i);
      y[id] = (int)motionEvent.getY(i);
      }
     
     switch (action){
     case MotionEvent.ACTION_DOWN:
      pointerAction[pointerId] = "ACTION_DOWN";
      break;
     case MotionEvent.ACTION_POINTER_DOWN:
      pointerAction[pointerId] = "ACTION_POINTER_DOWN";
      break;
     case MotionEvent.ACTION_MOVE:
      pointerAction[pointerId] = "ACTION_MOVE";
      
      int distance = (int) Math.sqrt(
        (x[0] - x[1]) * (x[0] - x[1]) +
        (y[0] - y[1]) * (y[0] - y[1]));
      textDistance.setText("distance: " + String.valueOf(distance));
      
      break;
     case MotionEvent.ACTION_UP:
      pointerAction[pointerId] = "ACTION_UP";
      break;
     case MotionEvent.ACTION_POINTER_UP:
      pointerAction[pointerId] = "ACTION_POINTER_UP";
      break;
     case MotionEvent.ACTION_CANCEL:
      pointerAction[pointerId] = "ACTION_CANCEL";
      break;
     default:
      pointerAction[pointerId] = "Unknown!";
     }

     currentPointer.setText(
       "action = " + pointerAction[pointerId] + "\n"
       + "pointerIndex = " + String.valueOf(pointerIndex) + "\n"
       + "pointerId = " + String.valueOf(pointerId) + "\n"
       + "getPointerCount() = " + motionEvent.getPointerCount() + "\n");
     
        pointerStatus_01.setText("[0] : "
          + String.valueOf(x[0]) + " : "
          + String.valueOf(y[0]));
        
        pointerStatus_02.setText("[1] : "
          + String.valueOf(x[1]) + " : "
          + String.valueOf(y[1]));
    }
   }
   
   return true; //means event have been processed
  }};
}

<?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"
   android:id="@+id/mainlayout"
   >
<TextView 
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:text="@string/hello"
   />
<TextView 
   android:id="@+id/currentpointer"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   />
<TextView 
   android:id="@+id/pointstatus_01"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   />
<TextView 
   android:id="@+id/pointstatus_02"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   />
<TextView 
   android:id="@+id/distance"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   />
</LinearLayout>

Refer Android Document for more details about android.view.MotionEvent

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