Android WebView实现顶部进度条

<RelativeLayout

  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="vertical" 
  <WebView
   android:id="@+id/webView"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:layout_below="@+id/toolbar_container" / 

  <ProgressBar

   android:id="@+id/progressBar"
   style="@style/crowd_item_progressBar"
   android:layout_width="match_parent"
   android:layout_height="3dp"
   android:layout_below="@+id/toolbar_container"
   android:background="@drawable/crowd_progressbar_unselect" / 

</RelativeLayout 

<style name="crowd_item_progressBar" 
  <item name="android:indeterminateOnly" false</item 
  <item name="android:progressDrawable" @drawable/crowd_progressbar_background</item 
  <item name="android:minHeight" 10dp</item 
  <item name="android:maxHeight" 10dp</item 

</style 

<layer-list xmlns:android="http://schemas.android.com/apk/res/android" 
 <item
  android:id="@android:id/progress"  
  <clip 
   <shape 
    <solid android:color="@color/selected"/ 
    <!--<corners android:radius="1.5dp"/ -- 
   </shape 
  </clip 
 </item 
</layer-list 

public class WebChromeClient extends android.webkit.WebChromeClient {
  @Override

  public void onProgressChanged(WebView view, int newProgress) {
   if (newProgress == 100) {

    mProgressBar.setVisibility(GONE);
   } else {

    if (mProgressBar.getVisibility() == GONE)
     mProgressBar.setVisibility(VISIBLE);
    mProgressBar.setProgress(newProgress);

   }

   super.onProgressChanged(view, newProgress);

  }

 }

 @Override
 protected void onScrollChanged(int l, int t, int oldl, int oldt) {
  LayoutParams lp = (LayoutParams) mProgressBar.getLayoutParams();
  lp.x = l;
  lp.y = t;
  mProgressBar.setLayoutParams(lp);
  super.onScrollChanged(l, t, oldl, oldt);

 }

}