webview加载网页的时候在标题栏上显示加载进度

public class ProgressTest extends Activity{

final Activity context = this;

@Override
public void onCreate(Bundle b) {
super.onCreate(b);
requestWindowFeature(Window.FEATURE_PROGRESS);//让进度条显示在标题栏上
setContentView(R.layout.main);

WebView webview = (WebView)findViewById(R.id.webview);
webview.setWebChromeClient(new WebChromeClient() {
public void onProgressChanged(WebView view, int progress) {
//Activity和Webview根据加载程度决定进度条的进度大小
//当加载到100%的时候 进度条自动消失
context.setProgress(progress * 100);
}
});
webview.loadUrl(url);
}