在将URL加载到WebView时显示ProgressBar

加载网址时是否可以显示进度条？我需要在进度栏中显示进度级别，可以使用自定义进度栏。但是我无法找到代码以获取有关已加载url的确切进度的信息。这是我当前的代码：

  public class MainActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    browser = (WebView)findViewById(R.id.webView1);
    progressBar = (ProgressBar)findViewById(R.id.progressBar);
    browser.setWebViewClient(new MyBrowser());
    browser.setWebChromeClient(new MyCustomChromeClient());
    mContext=this.getApplicationContext();
    browser.loadUrl(target_url);
    MainActivity.this.progressBar.setProgress(0);
}

private class MyBrowser extends WebViewClient {

    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        String host = Uri.parse(url).getHost();
        if (host.equals(target_url_prefix))
        {
            if(mWebviewPop!=null)
            {
                mWebviewPop.setVisibility(View.GONE);
                baseLayout.removeView(mWebviewPop);
                mWebviewPop=null;
            }
            return false;
        }

        if(host.equals("m.facebook.com"))
        {
            return false;
        }
        view.loadUrl(url);
        return true;
    }

    @Override
    public void onReceivedError(WebView view, int errorCode,
                                String description, String failingUrl) {
        noInternet();
    }

    @Override
    public void onPageStarted(WebView view, String url, Bitmap favicon) {
        visible();
    }

    @Override
    public void onPageFinished(WebView view, String url) {
        unvisible();
        System.out.println("\n" +view.getUrl());
        if(url.startsWith("https://m.facebook.com/v2.1/dialog/oauth")){
            if(mWebviewPop!=null)
            {
                mWebviewPop.setVisibility(View.GONE);
                baseLayout.removeView(mWebviewPop);
                mWebviewPop=null;
            }
            view.loadUrl(redirectUrl);
            return;
        }
        super.onPageFinished(view, url);
    }
}

private class MyCustomChromeClient extends WebChromeClient
{

    @Override
    public boolean onCreateWindow(WebView view, boolean isDialog,
                                  boolean isUserGesture, Message resultMsg) {
        mWebviewPop = new WebView(mContext);
        mWebviewPop.setVerticalScrollBarEnabled(false);
        mWebviewPop.setHorizontalScrollBarEnabled(false);
        mWebviewPop.setWebViewClient(new MyBrowser());
        mWebviewPop.getSettings().setJavaScriptEnabled(true);
        mWebviewPop.getSettings().setSavePassword(false);
        mWebviewPop.setLayoutParams(new RelativeLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
                ViewGroup.LayoutParams.MATCH_PARENT));
        baseLayout.addView(mWebviewPop);
        WebView.WebViewTransport transport = (WebView.WebViewTransport) resultMsg.obj;
        transport.setWebView(mWebviewPop);
        resultMsg.sendToTarget();

        return true;
    }

    @Override
    public void onCloseWindow(WebView window) {
    }

    @Override
    public void onProgressChanged(WebView view, int newProgress) {
        MainActivity.this.setValue(newProgress);
        super.onProgressChanged(view, newProgress);
    }
}
public void setValue(int progress) {
    this.progressBar.setProgress(progress);
}
}

如何获得加载网址的确切进度。使用此代码，我可以加载进度条，但显示为不确定的进度条。我想显示一个进度条，这是一个自定义视图。它应该显示成功加载URL的百分比。因此，我可以夸大自定义视图，但我又不知道如何获得准确的百分比。有人可以帮我这个代码。