Android实现带进度条的WebView

public class ProgressWebView extends WebView {

  private ProgressBar progressbar;

  public ProgressWebView(Context context, AttributeSet attrs) {
    super(context, attrs);
    progressbar = new ProgressBar(context, null,
        android.R.attr.progressBarStyleHorizontal);
    progressbar.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT,
        5, 0, 0));
    Drawable drawable = context.getResources().getDrawable(R.drawable.progress_bar_states);
    progressbar.setProgressDrawable(drawable);
    addView(progressbar);
    // setWebViewClient(new WebViewClient(){});
    setWebChromeClient(new WebChromeClient());
    //是否可以缩放
    getSettings().setSupportZoom(true);
    getSettings().setBuiltInZoomControls(true);
  }

  public class WebChromeClient extends android.webkit.WebChromeClient {
    @Override
    public void onProgressChanged(WebView view, int newProgress) {
      if (newProgress == 100) {
        progressbar.setVisibility(GONE);
      } else {
        if (progressbar.getVisibility() == GONE)
          progressbar.setVisibility(VISIBLE);
        progressbar.setProgress(newProgress);
      }
      super.onProgressChanged(view, newProgress);
    }
  }

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

<?xml version="1.0" encoding="utf-8"? 
<layer-list xmlns:android="http://schemas.android.com/apk/res/android"  
  <item android:id="@android:id/background" 
    <shape 
      <corners android:radius="2dp" / 
      <gradient
        android:angle="270"
        android:centerColor="#E3E3E3"
        android:endColor="#E6E6E6"
        android:startColor="#C8C8C8" / 
    </shape 
  </item 
  <item android:id="@android:id/progress" 
    <clip 
      <shape 
        <corners android:radius="2dp" / 

        <gradient
          android:centerColor="#4AEA2F"
          android:endColor="#31CE15"
          android:startColor="#5FEC46" / 
      </shape 
    </clip 
  </item 
</layer-list