ZoomControls控件是一个可以缩放控件，可以实现两个按钮控制图片的大小

<?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/layout"
>
<ImageView
android:id="@+id/image"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/foot"
/>

<ZoomControls
android:id="@+id/zoomcontrol"
android:layout_gravity="bottom"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
</LinearLayout>

package com.example.yanlei.my;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.os.Bundle;
import android.app.Activity;
import android.widget.Toast;
import android.view.Menu;
import android.view.MenuItem;
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.ImageView;
import android.widget.LinearLayout;
import android.widget.ZoomControls;

public class MainActivity extends AppCompatActivity {

private LinearLayout llLayout;
private ZoomControls zoomcontrols;
private ImageView img;
private int id = 0;
private int displayWidth;
private int displayHeight;
private float scaleWidth = 1;
private float scaleHeight = 1;
private Bitmap bitmap;

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

llLayout = (LinearLayout) findViewById(R.id.layout);
//取得屏幕分辨率大小
DisplayMetrics dm = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(dm);
displayWidth = dm.widthPixels;
//屏幕高度减去zoomControls的高度
displayHeight = dm.heightPixels;
bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.foot);
img = (ImageView) findViewById(R.id.image);
//zoom.hide();隐藏zoomControls
//zoom.show();显示zoomCOntrols

zoomcontrols = (ZoomControls) findViewById(R.id.zoomcontrol);
img = (ImageView) findViewById(R.id.image);
zoomcontrols.setIsZoomInEnabled(true);
zoomcontrols.setIsZoomOutEnabled(true);
//图片放大
zoomcontrols.setOnZoomInClickListener(new OnClickListener() {
public void onClick(View v) {
int bmpWidth = bitmap.getWidth();
int bmpHeight = bitmap.getHeight();
//设置图片放大但比例
double scale = 1.25;
//计算这次要放大的比例
scaleWidth = (float) (scaleWidth * scale);
scaleHeight = (float) (scaleHeight * scale);
//产生新的大小但Bitmap对象
Matrix matrix = new Matrix();
matrix.postScale(scaleWidth, scaleHeight);
Bitmap resizeBmp = Bitmap.createBitmap(bitmap, 0, 0, bmpWidth, bmpHeight, matrix, true);
img.setImageBitmap(resizeBmp);

}
});
//图片减小
zoomcontrols.setOnZoomOutClickListener(new OnClickListener() {

public void onClick(View v) {
int bmpWidth = bitmap.getWidth();
int bmpHeight = bitmap.getHeight();
//设置图片放大但比例
double scale = 0.8;
//计算这次要放大的比例
scaleWidth = (float) (scaleWidth * scale);
scaleHeight = (float) (scaleHeight * scale);
//产生新的大小但Bitmap对象
Matrix matrix = new Matrix();
matrix.postScale(scaleWidth, scaleHeight);
Bitmap resizeBmp = Bitmap.createBitmap(bitmap, 0, 0, bmpWidth, bmpHeight, matrix, true);
img.setImageBitmap(resizeBmp);
}

});
}
}