Android实现拖动进度条改变图片透明度

layout文件：

 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.hanqi.testapp2.PractiseActivity"
11     android:orientation="vertical">
12 
13     <SeekBar
14         android:layout_width="match_parent"
15         android:layout_height="wrap_content"
16         android:id="@+id/sb_1"
17         android:max="255"    //设置最大进度为255
18         android:progress="0"/>  //设置初始进度为0
19     <ImageView
20         android:layout_width="wrap_content"
21         android:layout_height="wrap_content"
22         android:src="@drawable/f4"
23         android:id="@+id/iv_1"/>
24 </LinearLayout>

java类代码：

 1 package com.hanqi.testapp2;
 2 
 3 import android.support.v7.app.AppCompatActivity;
 4 import android.os.Bundle;
 5 import android.widget.ImageView;
 6 import android.widget.SeekBar;
 7 
 8 public class PractiseActivity extends AppCompatActivity {
 9 
10     SeekBar sb_1;
11     ImageView iv_1;
12     @Override
13     protected void onCreate(Bundle savedInstanceState) {
14         super.onCreate(savedInstanceState);
15         setContentView(R.layout.activity_practise);
16         sb_1 =(SeekBar)findViewById(R.id.sb_1);
17         iv_1 =(ImageView)findViewById(R.id.iv_1);
18         iv_1.setImageAlpha(0);  //此步骤是设置一开始图片就为透明状态，不设置图片会在开始运行的时候显示
19         sb_1.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
20             @Override
21             public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
22 
23                 iv_1.setImageAlpha(progress);
24             }
25 
26             @Override
27             public void onStartTrackingTouch(SeekBar seekBar) {
28 
29             }
30 
31             @Override
32             public void onStopTrackingTouch(SeekBar seekBar) {
33 
34             }
35         });
36     }
37 }

效果为：