Android应用开发 ScaleGestureDetector（缩放手势检测）

 一、概述

ScaleGestureDetector这个类是专门用来检测两个手指在屏幕上做缩放的手势用的，最简单的应用就是用来缩放图片或者缩放网页。

二、要求

利用ScaleGestureDetector这个类实现图片缩放。

三、实现

新建工程MyScale，修改main.xml文件，在里面添加一个Button和一个SurfaceView，如下：

android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:orientation="vertical" >

android:id="@+id/button"

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="显示图片"

/>

android:id="@+id/surfaceview"

android:layout_width="fill_parent"

android:layout_height="fill_parent"

/>

修改MyScaleActivity.java文件，主要是实现按钮的监听和定义一个类实现ScaleGestureDetector.OnScaleGestureListener接口：

package com.nan.scale;

import android.app.Activity;

import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.graphics.Canvas;

import android.graphics.Color;

import android.graphics.Matrix;

import android.graphics.Rect;

import android.os.Bundle;

import android.view.MotionEvent;

import android.view.ScaleGestureDetector;

import android.view.SurfaceHolder;

import android.view.SurfaceView;

import android.view.View;

import android.widget.Button;

public class MyScaleActivity extends Activity

{

private Button mButton = null;

private SurfaceView mSurfaceView = null;

private SurfaceHolder mSurfaceHolder = null;

private ScaleGestureDetector mScaleGestureDetector = null;

private Bitmap mBitmap = null;

@Override

public void onCreate(Bundle savedInstanceState)

{

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

mSurfaceView = (SurfaceView)this.findViewById(R.id.surfaceview);

mSurfaceHolder = mSurfaceView.getHolder();

mScaleGestureDetector = new ScaleGestureDetector(this,new ScaleGestureListener());

mButton = (Button)this.findViewById(R.id.button);

//按钮监听

mButton.setOnClickListener(new View.OnClickListener()

{

@Override

public void onClick(View v)

{

// TODO Auto-generated method stub

mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.mmm);

//锁定整个SurfaceView

Canvas mCanvas = mSurfaceHolder.lockCanvas();

//画图

mCanvas.drawBitmap(mBitmap, 0f, 0f, null);

//绘制完成，提交修改

mSurfaceHolder.unlockCanvasAndPost(mCanvas);

//重新锁一次

mSurfaceHolder.lockCanvas(new Rect(0, 0, 0, 0));

mSurfaceHolder.unlockCanvasAndPost(mCanvas);

}

});

}

@Override

public boolean onTouchEvent(MotionEvent event)

{

//返回给ScaleGestureDetector来处理

return mScaleGestureDetector.onTouchEvent(event);

}

public class ScaleGestureListener implements ScaleGestureDetector.OnScaleGestureListener

{

@Override

public boolean onScale(ScaleGestureDetector detector)

{

// TODO Auto-generated method stub

Matrix mMatrix = new Matrix();

//缩放比例

float scale = detector.getScaleFactor()/3;

mMatrix.setScale(scale, scale);

//锁定整个SurfaceView

Canvas mCanvas = mSurfaceHolder.lockCanvas();

//清屏

mCanvas.drawColor(Color.BLACK);

//画缩放后的图

mCanvas.drawBitmap(mBitmap, mMatrix, null);

//绘制完成，提交修改

mSurfaceHolder.unlockCanvasAndPost(mCanvas);

//重新锁一次

mSurfaceHolder.lockCanvas(new Rect(0, 0, 0, 0));

mSurfaceHolder.unlockCanvasAndPost(mCanvas);

return false;

}

@Override

public boolean onScaleBegin(ScaleGestureDetector detector)

{

// TODO Auto-generated method stub

//一定要返回true才会进入onScale()这个函数

return true;

}

@Override

public void onScaleEnd(ScaleGestureDetector detector)

{

// TODO Auto-generated method stub

}

}

}