Android手机开发：图片的放大和缩小显示ImageView

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.LinearLayout;

public class ImageZoomActivity extends Activity {
private Button myButtonZoomIn;
private Button myButtonZoomOut;
private LinearLayout myImgLayout;
private ImageView myImageView;
private Bitmap bmp;
private int id = 0;
private int displayWidth;
private int displayHeight;
private float scaleWidth = 1;
private float scaleHeight = 1;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.zoom_in_out);

//取得屏幕分辨率大小
DisplayMetrics dm = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(dm);
displayWidth = dm.widthPixels;
//高度为屏幕分辨率，减去按钮高度
displayHeight = dm.heightPixels - 80;
//初始化bmp
bmp = BitmapFactory.decodeResource(getResources(), R.drawable.imgqr);

myImageView = (ImageView)findViewById(R.id.imageView);
myButtonZoomIn = (Button) findViewById(R.id.ZoomInButton);
myButtonZoomOut = (Button) findViewById(R.id.ZoomOutButton);
myImgLayout = (LinearLayout) findViewById(R.id.imglayout);
myButtonZoomIn.setOnClickListener(new Button.OnClickListener() {
@Override
public void onClick(View v) {
big();
}
});
myButtonZoomOut.setOnClickListener(new Button.OnClickListener() {
@Override
public void onClick(View v) {
small();
}
});
}

//图片缩小的方法
private void small() {
int bmpWidth = bmp.getWidth();
int bmpHeight = bmp.getHeight();
//设置图片缩小比例
double scale = 0.8;
//计算出这次要缩小的比例
scaleWidth = (float) (scaleWidth * scale);
scaleHeight = (float) (scaleHeight * scale);

//产生ReSize之后的bmp对象
Matrix matrix = new Matrix();
matrix.postScale(scaleWidth, scaleHeight);
Bitmap resizeBmp = Bitmap.createBitmap(bmp, 0, 0, bmpWidth, bmpHeight, matrix, true);
if(id == 0) {
//如果是第一次按，就删除原来默认的ImageView
myImgLayout.removeView(myImageView);
}else {
//否则，删除上一次放大缩小后产生的ImageView
myImgLayout.removeView((ImageView)findViewById(id));
}
//产生新的ImageView，并放入 resize的Bmp图像，再放入Layout
id++;
ImageView imageView = new ImageView(ImageZoomActivity.this);
imageView.setId(id);
imageView.setImageBitmap(resizeBmp);
myImgLayout.addView(imageView);
myButtonZoomIn.setEnabled(true);
//如果太小，则将缩小按钮设为false
if(scaleWidth*scale*bmpWidth<10 || scaleHeight*scale*bmpHeight<10) {
myButtonZoomOut.setEnabled(false);
}
}

//图片放大的方法
private void big() {
int bmpWidth = bmp.getWidth();
int bmpHeight = bmp.getHeight();
//设置图片放大比例
double scale = 1.25;
//计算出这次要缩小的比例
scaleWidth = (float) (scaleWidth * scale);
scaleHeight = (float) (scaleHeight * scale);
//产生ReSize之后的bmp对象
Matrix matrix = new Matrix();
matrix.postScale(scaleWidth, scaleHeight);
Bitmap resizeBmp = Bitmap.createBitmap(bmp, 0, 0, bmpWidth, bmpHeight, matrix, true);
if(id == 0) {
//如果是第一次按，就删除原来默认的ImageView
myImgLayout.removeView(myImageView);
}else {
//否则，删除上一次放大缩小后产生的ImageView
myImgLayout.removeView((ImageView)findViewById(id));
}
//产生新的ImageView，并放入 resize的Bmp图像，再放入Layout
id++;
ImageView imageView = new ImageView(ImageZoomActivity.this);
imageView.setId(id);
imageView.setImageBitmap(resizeBmp);
myImgLayout.addView(imageView);
myButtonZoomOut.setEnabled(true);
//如果再放大将超过屏幕大小，则设置放大按钮为false
if(scaleWidth*scale*bmpWidth>displayWidth || scaleHeight*scale*bmpHeight>displayHeight) {
myButtonZoomIn.setEnabled(false);
}
}

}

<?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="wrap_content">
<RelativeLayout
android:id="@+id/main"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<LinearLayout
android:id="@+id/imglayout"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical">

<ImageView
android:id="@+id/imageView"
android:src="@drawable/imgqr"
android:layout_width="fill_parent"
android:layout_height="wrap_content"/>
</LinearLayout>

<LinearLayout
android:id="@+id/bottom_panel"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:layout_alignParentBottom="true"
>
<Button
android:id="@+id/ZoomInButton"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:layout_gravity="center_vertical"
android:text="Zoom In"
/>
<Button
android:id="@+id/ZoomOutButton"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:layout_gravity="center_vertical"
android:text="Zoom Out"
/>
</LinearLayout>
</RelativeLayout>
</LinearLayout>