Android WebView shouldOverrideUrlLoading and redirect

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.

_webView.setWebViewClient(new WebViewClient() {
  @Override
  public boolean shouldOverrideUrlLoading(WebView view, String url) {
    boolean shouldOverride = false;
    if (url.startsWith("https://")) { //NON-NLS
      // DO SOMETHING
      shouldOverride = true;
    }
    return shouldOverride;
  }
}

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

Issue – does not work on all devices

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.

Workaround – onPageStarted

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

Usage is quite the same as shouldOverrideUrlLoading:

_webView.setWebViewClient(new WebViewClient() {
  @Override
  public void onPageStarted(WebView view, String url, Bitmap favicon){
    if (url.startsWith("https://")) { //NON-NLS
      view.stopLoading();
      // DO SOMETHING
    }
  }
} 

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.

Proguard and the @Subscribe Annotation used by Guava EventBus

We recently stumbled over an issue regarding the usage of com.google.common.eventbus.EventBus from the Google Guava Libraries and the default processing Proguard applies to your bytecode.

The EventBus provides an easy to use observer implementation for app internal messaging without the need to explicitly register event handler methods. Instead of providing an interface Guavas EventBus identifies the appropriate methods via an @Subscribe annotation.

@Subscribe
public void onEvent(MyEvent event) {
}

As part of Proguards shrinking and obfuscation process all annotations are removed by default and method names are obfuscated. The event handling methods can no longer be identified by the EventBus at runtime. So events sent to the EventBus will no longer be dispatched.

Following lines have to be addd to the proguard.cfg file to fix that

-keepattributes *Annotation*

-keepclassmembers class * {
       public void *(MyEvent);
}