WebView shouldOverrideUrlLoading 不触发原因

WebView shouldOverrideUrlLoading and redirect问题 

2012-11-23 11:36:46|  分类： Android |  标签： |字号大中小 订阅

问题：客户端界面中打开安卓市场某款产品的下载界面。点击下载按钮后，并不走客户端写在shouldOverrideUrlLoading中的处理逻辑。导致该包不能下载。

ps：安卓市场下载按钮是通过js跳转的。

原来，android平台下，在ApiLevel小于11的情况下，webview的shouldOverrideUrlLoading并不是每次都会调用。

所以需要添加平台适配。或者将放在shouldOverrideUrlLoading中的逻辑放在onPageStarted方法中去处理。

Androids WebView class provides a method called shouldOverrideUrlLoading to intercept the loading of the requested URLs.
This gives us the ability to suppress loading of the given URL or handle a URL in the external browser for example.

If you want to prevent the webview from loading the URL you have to return true. Otherwise the url is forwarded to the webview as usual.

1. _webView.setWebViewClient(new WebViewClient() { 
2.   @Override 
3.   public boolean shouldOverrideUrlLoading(WebView view, String url) { 
4.     boolean shouldOverride = false; 
5.     if (url.startsWith("https://")) { //NON-NLS 
6.       // DO SOMETHING 
7.       shouldOverride = true; 
8.     } 
9.     return shouldOverride; 
10.   } 
11. } 

This mechanism works fine for all URLs triggered by a user tapping on a link.

Unfortunately this method does not get invoked if the URLs source is a redirect on devices running Android < 3.0 (API Level 10 and lower).
Although it will be invoked an works just fine on devices with Android >= 3.0 (API Level 11 and up).

Android < 3.0 -> shouldOverrideUrlLoading will not be called on redirects

Android >= 3.0 -> shouldOverrideUrlLoading will be called even on redirects

You can find some fellow developers facing the same issue.

As a Workaround we use the recommended onPageStarted(WebView view, String url, Bitmap favicon)

Usage is quite the same as shouldOverrideUrlLoading:

1. _webView.setWebViewClient(new WebViewClient() { 
2.   @Override 
3.   public void onPageStarted(WebView view, String url, Bitmap favicon){ 
4.     if (url.startsWith("https://")) { //NON-NLS 
5.       view.stopLoading(); 
6.       // DO SOMETHING 
7.     } 
8.   } 
9. }  

With view.stopLoading the webview will stop loading of the new URL and still show the current content. This equals the behavior of shouldOverrideUrlLoading returning true.

The advantage is it works on all Android versions.

However the drawback is onPageStarted is invoked AFTER the page was requested form server. That means, the request is already sent to the server even if the response is afterward ignored.

The method shouldOverrideUrlLoading would let you omit the request BEFORE it is sent. So you would be able to save the outgoing web request.