问在android中如何在加载url到webview时显示进度？

EN

import android.app.Activity;
import android.app.AlertDialog;
import android.app.ProgressDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.Window;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Toast;

public class Main extends Activity {
    private WebView webview;
    private static final String TAG = "Main";
    private ProgressDialog progressBar;  

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        requestWindowFeature(Window.FEATURE_NO_TITLE);

        setContentView(R.layout.main);

        this.webview = (WebView)findViewById(R.id.webview);

        WebSettings settings = webview.getSettings();
        settings.setJavaScriptEnabled(true);
        webview.setScrollBarStyle(WebView.SCROLLBARS_OUTSIDE_OVERLAY);

        final AlertDialog alertDialog = new AlertDialog.Builder(this).create();

        progressBar = ProgressDialog.show(Main.this, "WebView Example", "Loading...");

        webview.setWebViewClient(new WebViewClient() {
            public boolean shouldOverrideUrlLoading(WebView view, String url) {
                Log.i(TAG, "Processing webview url click...");
                view.loadUrl(url);
                return true;
            }

            public void onPageFinished(WebView view, String url) {
                Log.i(TAG, "Finished loading URL: " +url);
                if (progressBar.isShowing()) {
                    progressBar.dismiss();
                }
            }

            public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
                Log.e(TAG, "Error: " + description);
                Toast.makeText(activity, "Oh no! " + description, Toast.LENGTH_SHORT).show();
                alertDialog.setTitle("Error");
                alertDialog.setMessage(description);
                alertDialog.setButton("OK", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int which) {
                        return;
                    }
                });
                alertDialog.show();
            }
        });
        webview.loadUrl("http://www.google.com");
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <WebView android:id="@string/webview"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_weight="1" />
</LinearLayout>

mWebView.setWebViewClient(new WebViewClient() {

        public void onPageStarted(WebView view, String url, Bitmap favicon) {
            if (progressBar!= null && progressBar.isShowing()) {
                progressBar.dismiss();
            }
            progressBar = ProgressDialog.show(WebViewActivity.this, "Application Name", "Loading...");
        }

        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            view.loadUrl(url);

            return true;
        }

        public void onPageFinished(WebView view, String url) {
            if (progressBar.isShowing()) {
                progressBar.dismiss();
            }
        }

        public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
            alertDialog.setTitle("Error");
            alertDialog.setMessage(description);
            alertDialog.setButton("OK", new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {
                    return;
                }
            });
            alertDialog.show();
        }
    });

 private ProgressBar progressBar;
 progressBar=(ProgressBar)findViewById(R.id.webloadProgressBar);
 WebView urlWebView= new WebView(Context);
    urlWebView.setWebViewClient(new AppWebViewClients(progressBar));
                        urlWebView.getSettings().setJavaScriptEnabled(true);
                        urlWebView.loadUrl(detailView.getUrl());

public class AppWebViewClients extends WebViewClient {
     private ProgressBar progressBar;

    public AppWebViewClients(ProgressBar progressBar) {
        this.progressBar=progressBar;
        progressBar.setVisibility(View.VISIBLE);
    }
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        // TODO Auto-generated method stub
        view.loadUrl(url);
        return true;
    }

    @Override
    public void onPageFinished(WebView view, String url) {
        // TODO Auto-generated method stub
        super.onPageFinished(view, url);
        progressBar.setVisibility(View.GONE);
    }
}