Android开发实现的图片浏览功能示例【放大图片】

<?xml version="1.0" encoding="utf-8"?>
<linearlayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  tools:context=".mainactivity"
  android:orientation="vertical">
  <linearlayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal">
    <button
      android:id="@+id/plus"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="增加透明度"
      android:layout_weight="1"/>
    <button
      android:id="@+id/minus"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="减少透明度"
      android:layout_weight="1"/>
    <button
      android:id="@+id/next"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="下一张"
      android:layout_weight="1"/>
  </linearlayout>
  <!--此处显示图片整体-->
  <imageview
    android:id="@+id/imagel"
    android:layout_width="wrap_content"
    android:layout_height="280dp"
    android:src="@drawable/xiaochouyu"
    android:scaletype="fitcenter"/>
  <imageview
    android:id="@+id/image2"
    android:layout_width="200dp"
    android:layout_height="200dp"
    android:background="#00f"
    android:layout_margin="5dp"/>
</linearlayout>

public class mainactivity extends appcompatactivity {
  //定义一个访问图片的数组
  int[] images = new int[]{
      r.drawable.xiaochouyu ,
      r.drawable.leidayu ,
      r.drawable.paodangyu ,
      r.drawable.huangjindiao ,
      r.drawable.piaopiao
  };
  //定义默认显示的图片
  int currentimg = 2 ;
  //定义图片初始透明度
  private int alpha = 255 ;
  @override
  protected void oncreate(bundle savedinstancestate) {
    super.oncreate(savedinstancestate);
    setcontentview(r.layout.activity_main);
    final button plus = (button) findviewbyid(r.id.plus) ;
    final button minus = (button) findviewbyid(r.id.minus) ;
    final button next = (button) findviewbyid(r.id.next) ;
    final imageview imageview01 = (imageview) findviewbyid(r.id.imagel);
    final imageview imageview02 = (imageview) findviewbyid(r.id.image2);
    //定义查看下一张图片的监听器
    next.setonclicklistener(new view.onclicklistener() {
      @override
      public void onclick(view v) {
        //显示下一张图片
        imageview01.setimageresource(images[currentimg++ % images.length]);
      }
    });
    //定义改变图片透明度的方法
    view.onclicklistener listener = new view.onclicklistener() {
      @requiresapi(api = build.version_codes.jelly_bean)
      @override
      public void onclick(view v) {
        if (v == plus){
          alpha = alpha + 20 ;
        }
        if (v == minus){
          alpha = alpha - 20 ;
        }
        if (alpha >= 255){
          alpha = 255 ;
        }
        if (alpha <= 0){
          alpha = 0 ;
        }
        imageview01.setimagealpha(alpha);
      }
    };
    //为两个按钮添加监听器
    plus.setonclicklistener(listener);
    minus.setonclicklistener(listener);
    imageview01.setontouchlistener(new view.ontouchlistener() {
      @requiresapi(api = build.version_codes.jelly_bean)
      @override
      public boolean ontouch(view v, motionevent event) {
        bitmapdrawable bitmapdrawable = (bitmapdrawable) imageview01.getdrawable();
        //获取第一个托片显示框中的位图
        bitmap bitmap = bitmapdrawable.getbitmap();
        //bitmap图片实际大小与第一个imageview的缩放比例
        double scale = 1.0 * bitmap.getheight() / imageview01.getheight();
        //获取需要显示的图片开始点
        int x = (int) (event.getx() * scale);
        int y = (int) (event.gety() * scale);
        if (x + 120 > bitmap.getwidth()){
          x = bitmap.getwidth() - 120 ;
        }
        if (y + 120 > bitmap.getheight()){
          y = bitmap.getheight() - 120 ;
        }
        //显示图片的指定区域
        imageview02.setimagebitmap(bitmap.createbitmap(bitmap , x , y , 120 , 120));
        imageview02.setimagealpha(alpha);
        return false;
      }
    });
  }
}