在Android里面图片的缩放，有很多方法，这里介绍一种比较简单的。它主要采用BitMap对象的切换，通过BitMap的比例缩放改变来实现图片的放大放小。下面是效果图：
程序代码：
（1）布局：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout android:id="@+id/relativeLayout"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="center_horizontal"
xmlns:android="http://schemas.android.com/apk/res/android">
<ImageView android:id="@+id/imageView"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="center"
>
</ImageView>
<LinearLayout android:id="@+id/linearLayout"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true">
<Button android:id="@+id/bt_smaller"
android:layout_width="100px"
android:layout_height="50px"
android:text="缩小" >
</Button>
<Button android:id="@+id/bt_bigger"
android:layout_width="100px"
android:layout_height="50px"
android:text="放大" >
</Button>
</LinearLayout>
</RelativeLayout>
（2）代码：
package com.myandroid.test;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.RelativeLayout;
public class AlterImageSize extends Activity {
private ImageView imageView;
private Button bt_bigger;
private Button bt_smaller;
private RelativeLayout layout; //容器
private Bitmap bmp; //bitmap图片对象
private int primaryWidth; //原图片宽
private int primaryHeight; //原图片高
private double scaleWidth, scaleHeight; //高宽比例
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//初始化
getWidget();
}
/**
* 获取控件对象并初始化
*/
private void getWidget() {
imageView = (ImageView)findViewById(R.id.imageView);
layout = (RelativeLayout)findViewById(R.id.relativeLayout);
bt_bigger = (Button)findViewById(R.id.bt_bigger);
bt_smaller = (Button)findViewById(R.id.bt_smaller);
//创建BitMap对象，用于显示图片
bmp = BitmapFactory.decodeResource(this.getResources(), R.drawable.butterfly);
//原始大小
primaryWidth = bmp.getWidth();
primaryHeight = bmp.getHeight();
//初始比例为1
scaleWidth = scaleHeight = 1;
imageView.setImageBitmap(bmp);
bt_bigger.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
scale(1.25, 1.25);
}
});
bt_smaller.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
scale(0.8, 0.8);
}
});
}
/**
* 缩放
*/
private void scale(double scale_width, double scale_height) {
//这种方法，有点不好是：如果图片大小超出屏幕会报错。
if((scale_width > 1 && scaleWidth * primaryWidth >= getWindowManager().getDefaultDisplay().getWidth())
|| (scale_width > 1 && scale_height * primaryHeight >= getWindowManager().getDefaultDisplay().getHeight())){
bt_bigger.setEnabled(false);
}else {
bt_bigger.setEnabled(true);
}
scaleWidth = scaleWidth * scale_width; //缩放到原来的*倍
scaleHeight = scaleHeight * scale_height;
Matrix matrix = new Matrix(); //矩阵，用于图片比例缩放
matrix.postScale((float)scaleWidth, (float)scaleHeight); //设置高宽比例（三维矩阵）
//缩放后的BitMap
Bitmap newBmp = Bitmap.createBitmap(bmp, 0, 0, primaryWidth, primaryHeight, matrix, true);
//重新设置BitMap
imageView.setImageBitmap(newBmp);
}
}