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I have an app that heavily uses the Android WebView to display my custom HTML content. The latest Android update (4.4/Kit-Kat/SDK-19) featured a redesigned WebView.

One of my users with a Nexus 5 reported a problem where some links cause the app to crash. I ran in the 4.4 emulator and debug into my WebViewClient's shouldOverrideUrlLoading() method. On all previously tested Android versions (2.2-4.3) the url String passed into the method had my custom url with "/" characters in it. In 4.4 the exact same link now has "\" characters in their place.

This doesn't make any sense to me. I load the HTML exactly the same, so somehow the new WebView converted all my slashes into backslashes.

Why does the new WebView do this?

Jon
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4 Answers4

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I did more debugging and discovered I actually have the question reversed. Turns out the older versions of WebView did conversions of the URL, not the new one.

I load HTML with a format similar to this into a WebView:

    <a href="this\\is\\my\\custom\\path">link</a>

I use the double back slashes as delimiters and parse the data later when the link is clicked. In older versions of WebView it converted my double backslash characters into forward slashes. It had been so long since I was in that code, I forgot I adjusted my code to use forward slashes rather than the backslashes in the original HTML.

The new version of WebView leaves my custom URL intact, giving me the exact same string as my original HTML. So turns out the old WebView is the problem not the new one.

Jon
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  • Could you help me with this , http://stackoverflow.com/questions/20582282/uncaught-referenceerror-while-loading-asset-file-on-android-4-4 – Shakti Malik Dec 14 '13 at 16:16
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Changes in URL handling are a known issue. Please see the migration guide for more detail.

The behaviour in this particular case will depend on what your base URL's scheme is, from what you're describing I'm guessing your base URL's scheme is "http(s)://" in which case the Chromium WebView performs URL normalization.

You might want to consider using the URI class to handle the discrepancy between the Classic and Chromium WebViews in this case.

marcin.kosiba
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  • Originally I accepted my own answer because it was the immediate answer to my problem, but this answer has helped me a few other places where I had some custom href values that were getting messed up because of how 4.4 was handling my custom urls. So thanks! – Jon Dec 10 '13 at 18:06
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The new WebView applies additional restrictions when requesting resources and resolving links that use a custom URL scheme. For example, if you implement callbacks such as shouldOverrideUrlLoading() or shouldInterceptRequest(), then WebView invokes them only for valid URLs.

If you are using a custom URL scheme or a base URL and notice that your app is receiving fewer calls to these callbacks or failing to load resources on Android 4.4, ensure that the requests specify valid URLs that conform to RFC 3986.

For example, the new WebView may not call your shouldOverrideUrlLoading() method for links like this:

Show Profile The result of the user clicking such a link can vary:

If you loaded the page by calling loadData() or loadDataWithBaseURL() with an invalid or null base URL, then you will not receive the shouldOverrideUrlLoading() callback for this type of link on the page. Note: When you use loadDataWithBaseURL() and the base URL is invalid or set null, all links in the content you are loading must be absolute.

If you loaded the page by calling loadUrl() or provided a valid base URL with loadDataWithBaseURL(), then you will receive the shouldOverrideUrlLoading() callback for this type of link on the page, but the URL you receive will be absolute, relative to the current page. For example, the URL you receive will be "http://www.example.com/showProfile" instead of just "showProfile". Instead of using a simple string in a link as shown above, you can use a custom scheme such as the following:

<a href="example-app:showProfile">Show Profile</a>

You can then handle this URL in your shouldOverrideUrlLoading() method like this:

// The URL scheme should be non-hierarchical (no trailing slashes)
  private static final String APP_SCHEME = "example-app:";

@Override
public boolean shouldOverrideUrlLoading(WebView view, String url) {
    if (url.startsWith(APP_SCHEME)) {
        urlData = URLDecoder.decode(url.substring(APP_SCHEME.length()), "UTF-8");
       respondToData(urlData);
        return true;
    }
    return false;
}

If you can't alter the HTML then you may be able to use loadDataWithBaseURL() and set a base URL consisting of a custom scheme and a valid host, such as "example-app:///". For example:

webView.loadDataWithBaseURL("example-app://example.co.uk/", HTML_DATA,
    null, "UTF-8", null);

The valid host name should conform to RFC 3986 and it's important to include the trailing slash at the end, otherwise, any requests from the loaded page may be dropped.

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to avoid webview below 4.4 convert backslash to forward slash, I just escape my url, then in Java code, use URI.decode to get the real url.That works for me.

Bruce
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