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;
      }
    });
  }
}