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

 <?xml version="1.0" encoding="utf-8"?>

 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

     xmlns:tools="http://schemas.android.com/tools"

     android:layout_width="match_parent"

     android:layout_height="match_parent"

     android:paddingBottom="@dimen/activity_vertical_margin"

     android:paddingLeft="@dimen/activity_horizontal_margin"

     android:paddingRight="@dimen/activity_horizontal_margin"

     android:paddingTop="@dimen/activity_vertical_margin"

     tools:context="com.example.administrator.hello3.MainActivity"

     android:orientation="vertical"

     android:layout_gravity="center"

     >

     <LinearLayout

         android:orientation="horizontal"

         android:layout_width="wrap_content"

         android:layout_height="wrap_content"

         android:layout_gravity="center">

         <Button

             android:id="@+id/btn_add"

             android:layout_width="wrap_content"

             android:layout_height="wrap_content"

             android:text="增加" />

         <Button

             android:id="@+id/btn_reduce"

             android:layout_width="wrap_content"

             android:layout_height="wrap_content"

             android:text="减少" />

         <Button

             android:id="@+id/btn_next"

             android:layout_width="wrap_content"

             android:layout_height="wrap_content"

             android:text="下一张" />

     </LinearLayout>

     <ImageView

         android:layout_gravity="center"

         android:id="@+id/iv"

         android:src="@mipmap/ic_launcher"

         android:layout_width="wrap_content"

         android:layout_height="wrap_content" />

 </LinearLayout>

3.MainActivity.java

 package com.example.administrator.hello3;

 import android.support.v7.app.AppCompatActivity;

 import android.os.Bundle;

 import android.view.View;

 import android.widget.Button;

 import android.widget.ImageView;

 public class MainActivity extends AppCompatActivity {

     private Button button_add,button_reduce,button_next;

     private ImageView imageView;

     private  int alpha=255;

     private int current=0;

     private int[] pics = {R.drawable.pic1,R.drawable.pic2,R.drawable.pic3,R.drawable.pic4};

     @Override

     protected void onCreate(Bundle savedInstanceState) {

         super.onCreate(savedInstanceState);

         setContentView(R.layout.activity_main);

         setContentView(R.layout.activity_main);

         button_add=(Button)findViewById(R.id.btn_add);

         button_reduce=(Button)findViewById(R.id.btn_reduce);

         button_next=(Button)findViewById(R.id.btn_next);

         imageView=(ImageView) findViewById(R.id.iv);

         MyListener myListener = new MyListener();

         button_add.setOnClickListener(myListener);

         button_reduce.setOnClickListener(myListener);

         button_next.setOnClickListener(new View.OnClickListener() {

             @Override

             public void onClick(View v) {

                 imageView.setImageResource(pics[current++%pics.length]);

             }

         });

     }

     class  MyListener implements View.OnClickListener{

         @Override

         public void onClick(View v) {

             if(v==button_add){

                 alpha+=20;

                 if(alpha>=255){

                     alpha=255;

                 }

             }else if(v==button_reduce) {

                 alpha -= 20;

                 if (alpha <= 0) {

                     alpha = 0;

                 }

             }

             imageView.setImageAlpha(alpha);

         }

     }

 }

3.drawable下面加入自己的图片