android手指缩放效果

写这篇文章，是因为试了这篇《Android通过手势实现的缩放处理》http://www.oschina.net/code/snippet_16_2735 介绍的缩放代码在（G11 android2.3.3）上运行，完成没有缩放效果，只有一个蓝色的圆，跟着手指移动。。。。只好自己看下 android自带的demo和API，自己实现下缩放效果。
MotionEvent类中有个方法getActionMasked()，这个方法可以检查触摸的状态:
当只有一个触摸点时（只用一根手指触摸屏幕），按下是0，起来是1，移动是2；
当触摸点多于1时（多根手指触摸屏幕），按下是5，起来是6，移动是2；
可以使用MotionEvent的getPointerCount()方法检查当前屏幕有多少个触摸点。
实现代码在《Android通过手势实现的缩放处理》的基础上做了点修改。

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;

public class MultiTouchTestActivity extends Activity{
@Override
public void onCreate(BundlesavedInstanceState){
super .onCreate(savedInstanceState);
Viewview = new MultiTouchView( this );

setContentView(view);

}

class MultiTouchView extends View{
private float x1;
private float y1;
private float x2;
private float y2;

private float r = 30F;
private float r1 = 0F;
private float r2 = 0F;
private int max = 0 ;
public MultiTouchView(Contextcontext){
super (context);
}

@Override
public boolean onTouchEvent(MotionEventevent){
int action = event.getActionMasked();
int p = event.getPointerCount(); // 接触点数
int N = event.getHistorySize();
if (N > max){
max = N;
}

Stringsff = " " ;
// 只处理两点触摸
if (p == 2 && action == MotionEvent.ACTION_POINTER_1_DOWN){
x1 = event.getX( 0 );
y1 = event.getY( 0 );
x2 = event.getX( 1 );
y2 = event.getY( 1 );

}
// 只处理两点触摸
if (p == 2 && action == MotionEvent.ACTION_MOVE){
r1 = ( float )Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2)
* (y1 - y2)) / 2 ;
float tx1 = event.getX( 0 );
float ty1 = event.getY( 0 );
float tx2 = event.getX( 1 );
float ty2 = event.getY( 1 );
r2 = ( float )Math.sqrt((tx1 - tx2) * (tx1 - tx2) + (ty1 - ty2)
* (ty1 - ty2)) / 2 ;
}
if (p == 2 && action == MotionEvent.ACTION_POINTER_1_UP){
r = r + (r2 - r1);
}
if (p == 1 ){
x1 = event.getX( 0 );
y1 = event.getY( 0 );
}
for ( int j = 0 ;j < p;j ++ ){
int x = ( int )event.getX(j);
int y = ( int )event.getY(j);
sff = sff + " ( " + x + " , " + y + " ) " ;
}

MultiTouchTestActivity. this .setTitle(String.valueOf(action + " " + p + " r: " + ( int )r) + " r1: " +

( int )r1 + " r2: " + ( int )r2);
invalidate();
return true ;

}

@Override
protected void onDraw(Canvascanvas){
super .onDraw(canvas);
Paintpaint = new Paint();
paint.setColor(Color.BLUE);
canvas.drawCircle(x1,y1,r + r2 - r1,paint);
}
}
} 在AVD（android2.3.3）中运行效果

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