图像视图-ImageView

（一）

知识点：

（1）imageView.setImageAlpha(Alpha):设置图片透明度

（2）在布局imageView中设置图片位置：android:scaleType="center"

android:scaleType="center"

1.效果图：点击增加图片透明度增加，点击减少图片透明度减少，点击下一张显示下一张图片

2.activity_main.xml

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 3     xmlns:tools="http://schemas.android.com/tools"
 4     android:layout_width="match_parent"
 5     android:layout_height="match_parent"
 6     android:paddingBottom="@dimen/activity_vertical_margin"
 7     android:paddingLeft="@dimen/activity_horizontal_margin"
 8     android:paddingRight="@dimen/activity_horizontal_margin"
 9     android:paddingTop="@dimen/activity_vertical_margin"
10     tools:context="com.example.administrator.hello3.MainActivity"
11     android:orientation="vertical"
12     android:layout_gravity="center"
13     >
14 
15     <LinearLayout
16         android:orientation="horizontal"
17         android:layout_width="wrap_content"
18         android:layout_height="wrap_content"
19         android:layout_gravity="center">
20         <Button
21             android:id="@+id/btn_add"
22             android:layout_width="wrap_content"
23             android:layout_height="wrap_content"
24             android:text="增加" />
25         <Button
26             android:id="@+id/btn_reduce"
27             android:layout_width="wrap_content"
28             android:layout_height="wrap_content"
29             android:text="减少" />
30         <Button
31             android:id="@+id/btn_next"
32             android:layout_width="wrap_content"
33             android:layout_height="wrap_content"
34             android:text="下一张" />
35     </LinearLayout>
36     <ImageView
37         android:layout_gravity="center"
38         android:id="@+id/iv"
39         android:src="@mipmap/ic_launcher"
40         android:layout_width="wrap_content"
41         android:layout_height="wrap_content" />
42 </LinearLayout>

3.MainActivity.java

 1 package com.example.administrator.hello3;
 2 
 3 import android.support.v7.app.AppCompatActivity;
 4 import android.os.Bundle;
 5 import android.view.View;
 6 import android.widget.Button;
 7 import android.widget.ImageView;
 8 
 9 public class MainActivity extends AppCompatActivity {
10     private Button button_add,button_reduce,button_next;
11     private ImageView imageView;
12     private  int alpha=255;
13     private int current=0;
14     private int[] pics = {R.drawable.pic1,R.drawable.pic2,R.drawable.pic3,R.drawable.pic4};
15 
16     @Override
17     protected void onCreate(Bundle savedInstanceState) {
18         super.onCreate(savedInstanceState);
19         setContentView(R.layout.activity_main);
20 
21         setContentView(R.layout.activity_main);
22 
23         button_add=(Button)findViewById(R.id.btn_add);
24         button_reduce=(Button)findViewById(R.id.btn_reduce);
25         button_next=(Button)findViewById(R.id.btn_next);
26         imageView=(ImageView) findViewById(R.id.iv);
27 
28         MyListener myListener = new MyListener();
29         button_add.setOnClickListener(myListener);
30         button_reduce.setOnClickListener(myListener);
31 
32         button_next.setOnClickListener(new View.OnClickListener() {
33             @Override
34             public void onClick(View v) {
35                 imageView.setImageResource(pics[current++%pics.length]);
36             }
37         });
38 
39 
40 
41     }
42     class  MyListener implements View.OnClickListener{
43         @Override
44         public void onClick(View v) {
45             if(v==button_add){
46                 alpha+=20;
47                 if(alpha>=255){
48                     alpha=255;
49                 }
50             }else if(v==button_reduce) {
51                 alpha -= 20;
52                 if (alpha <= 0) {
53                     alpha = 0;
54                 }
55             }
56             imageView.setImageAlpha(alpha);
57         }
58     }
59 
60 }

3.drawable下面加入自己的图片