ProgressBar跟随进度变化颜色渐变

     <ProgressBar 
            android:id="@+id/update_version_down_pb"
            style="?android:attr/progressBarStyleHorizontal"
            android:layout_width="match_parent"
            android:layout_centerHorizontal="true"
            android:layout_alignParentTop="true"
            android:layout_height="@dimen/dp4"
            android:max="100"
            android:progressDrawable="@drawable/progress_bar"/>

progress_bar样式文件
progress_bar.xml

<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >  
  
    <item android:id="@android:id/background">  
  
        <shape>  
  
            <corners android:radius="5dip" />  
  
            <gradient  
                android:endColor="#FFC0C0C0"  
                android:startColor="#FFC0C0C0" />  
        </shape>  
    </item>  
  
    <item android:id="@android:id/secondaryProgress">  
  
        <clip>  
  
            <shape>  
  
                <corners android:radius="5dip" />  
  
                <gradient  
                    android:endColor="#83E1FB"
                    android:startColor="#B6E1DA" />
            </shape>  
        </clip>  
    </item>  
  
    <item android:id="@android:id/progress">  
  
        <clip>  
  
            <shape>  
  
                <corners android:radius="5dip" />  
  
                <gradient  
                    android:angle="0"  
                    android:endColor="#83E1FB"
                    android:startColor="#B6E1DA" />
            </shape>  
        </clip>  
    </item>  
  
</layer-list>