通过 WebView.loadURL() 指定不存在的 URL 时，WebViewClient.onPageStarted( ) 被调用两次

Question

这是我的代码

public class Main extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);


    WebView webView = (WebView)findViewById(R.id.webView);

    // Assign webclient.
    webView.setWebViewClient(new WebViewClient( ) {
        @Override
        public void onPageStarted(WebView view, String url, Bitmap favicon) {
            Log.d("TAG", url);
        }

        @Override
        public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
            Log.d("TAG", "failed: " + failingUrl + ", error code: " + errorCode + " [" + description + "]");
        }
    });


    webView.loadUrl("http://m.vooglemoogle.com" );
}



}

---

结果如下日志：

03-29 13:40:27.005: DEBUG/TAG(10948): http://m.vooglemoogle.com/
03-29 13:40:27.599: DEBUG/TAG(10948): failed: http://m.vooglemoogle.com/, error code: -2[The URL could not be found.]
03-29 13:40:27.607: DEBUG/TAG(10948): http://m.vooglemoogle.com/

注意对 onPageStarted( ) 的另一个调用...有谁知道这背后的原因吗？ 干杯！

Answer 1

我在使用 API 7 的 AVD 上测试我的应用程序时遇到了同样的问题（不确定这是否相关，但无论如何）。

我注意到回调的确切顺序如下：

onPageStarted()     // url = non-existing url
onLoadResource()    // url = non-existing url
onReceivedError()   // url = non-existing url

onPageStarted()     // url = non-existing url
onLoadResource()    // url = file://android_assed/webkit/android-weberror.png
onPageFinished()    // url = non-existing url

所以我猜测 Android“网页不可用”页面的加载正在触发第二个 onPageStarted 调用。

Answer 2

我也曾为此苦苦挣扎，但我想我已经解决了。基本上，我设置了一个错误标志，以防止客户端处理更多回调。当我调用活动中的方法以再次尝试加载时，该标志会重置。这是我创建的要点中的一些示例代码 https://gist.github.com/museofwater/6373048

public class AsyncMultiplayerSetupActivity extends Activity {

    private static final String TAG = AsyncMultiplayerSetupActivity.class.getName();
    public static final String UTF_8 = "UTF-8";

    private WebView wvSignin;
    private String url = "http://localhost:9000/signin";
    private ProgressDialog progressLoadUrl;
    private SigninWebViewClient webViewClient;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        Intent intent = getIntent();
        registerUser(url);
    }

    private void registerUser(String url) {
        webViewClient = new SigninWebViewClient(getResources().getInteger(R.integer.timeout));
        setContentView(R.layout.setup);
        wvSignin = (WebView)findViewById(R.id.wvSignin);
        wvSignin.getSettings().setJavaScriptEnabled(true);
        wvSignin.getSettings().setJavaScriptCanOpenWindowsAutomatically(true);
        wvSignin.setWebViewClient(webViewClient);
        loadUrl(url);
    }

    private void loadUrl(String url) {
        if (!NetworkUtil.checkNetwork(this)) {
            setSigninFailureResult();
        }
        // Show progress
        progressLoadUrl =
                ProgressDialog.show(this, getString(R.string.CONNECTING_TITLE),
                        getString(R.string.CONNECTING_MSG));
        webViewClient.prepareToLoadUrl();
        wvSignin.loadUrl(url);
    }

    private void setSigninFailureResult() {
        setResult(getResources().getInteger(R.integer.RESPONSE_FAILED_CODE));
        finish();
    }

    private void setSigninResult() {    
        setResult(getResources().getInteger(R.integer.RESPONSE_OK_CODE));
    }

    private class SigninWebViewClient extends WebViewClient {
        /**
         * Timeout for page load in seconds
         */
        private int timeout;
        private String urlLoading;

        boolean pageLoaded = false;

        // Flag to instruct the client to ignore callbacks after an error
        boolean hasError = false;

        private Handler timeoutHandler;
        private AlertDialog alertDialog;

        private SigninWebViewClient(int timeout) {
            this.timeout = timeout;
            timeoutHandler = new Handler();
        }

        // Called by activity before requesting load of a url
        private void prepareToLoadUrl() {
           this.hasError = false;
           this.pageLoaded = true;
           this.urlLoading = null;
        }

        @Override
        public void onPageStarted(WebView view, String url, Bitmap favicon) {
            if (hasError) {
                return;
            }
            urlLoading = url;
            // timeout has expired if this flag is still set when the message is handled
            pageLoaded = false;
            Runnable run = new Runnable() {
                public void run() {
                    // Do nothing if we already have an error
                    if (hasError) {
                        return;
                    }

                    // Dismiss any current alerts and progress
                    dismissProgress();
                    dismissErrorAlert();
                    if (!pageLoaded) {
                        showTimeoutAlert();
                    }
                }
            };
            timeoutHandler.postDelayed(run, this.timeout*1000);
        }

        @Override
        public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
            // Ignore future callbacks because the page load has failed
            hasError = true;
            dismissProgress();
            showServerErrorAlert();
        }

        @Override
        public void onPageFinished(WebView view, String url) {
            if (hasError) {
                return;
            }
            pageLoaded = true;
            dismissProgress();
            dismissErrorAlert();
            urlLoading = null;

            // Do whatever processing you need to on page load here
         }

        private void showTimeoutAlert() {
            showErrorAlert(R.string.TIMEOUT_TITLE, R.string.TIMEOUT_MSG);
        }

        private void showServerErrorAlert() {
            showErrorAlert(R.string.SERVER_ERROR_TITLE,R.string.SERVER_ERROR_MSG);
        }

        private void showErrorAlert(int titleResource, int messageResource) {
            AlertDialog.Builder builder = new AlertDialog.Builder(AsyncMultiplayerSetupActivity.this);
            // Add the buttons
            builder.setTitle(titleResource)
                    .setMessage(messageResource)
                    .setPositiveButton(R.string.RETRY, new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int id) {
                            // Try to load url again
                            loadUrl(urlLoading);
                            dialog.dismiss();
                        }
                    });
            builder.setNegativeButton(R.string.CANCEL, new DialogInterface.OnClickListener() {
                 public void onClick(DialogInterface dialog, int id) {
                     // User cancelled the dialog
                     setSigninFailureResult();
                     dialog.cancel();
                }
            });

            // Create the AlertDialog
            alertDialog = builder.create();
            alertDialog.show();
        }

        private void dismissProgress() {
            if (progressLoadUrl != null && progressLoadUrl.isShowing()) {
                progressLoadUrl.dismiss();
            }
        }

        private void dismissErrorAlert() {
            if (alertDialog != null && alertDialog.isShowing()) {
                alertDialog.dismiss();
            }
        }
    }
}

Answer 3

在android API中，你可以找到注释：

通知主机应用程序页面已开始加载。这
每个主框架加载都会调用一次方法，因此带有 iframe 的页面
或框架集将为主框架调用一次 onPageStarted 。这
也意味着 onPageStarted 不会被调用，当内容
嵌入的框架发生变化，即单击目标为
iframe。

这表明它可能是由网页中的“iframe”引起的。