Tuesday, July 29, 2014

Android - Making Facebook login works in HTML5 app hosted inside WebView

Context - Develop one app for all machines / platforms.

The software stake holders always want to target a large audience regardless of what machine / plat form their clients uses. That is one of the reason why software are often written as web application. If we write as web application, at least in theory it can run in any machine whether it is laptop,tablet or mobile also regardless of the OS Windows / Linux / Mac used in those machines. Another advantage going with web is the less development cost as we are developing one application. Its the trend among the developers / organizations.

There are so many arguments going on whether we should go with this HTML5 web apps to address this problem in case we are targeting mobile platforms only. Some people argue that we should go with Xamarin kind of converging platforms. But that won't help to run the app in laptops.

Another requirement from the stakeholder will be to have native web app even if we have working web application. That is to make sure the application is present in the app stores in the way standard mobile applications are present and users don't need to worry about the web application url. They just need to install the mobile app from the store.

So only one way to meet the above requirement of running in desktops, laptops and as native mobile app is to develop application using HTML5 and create native wrapper applications which uses WebBrowerControl / WebView to show the HTML5 web site inside the native mobile app.

But will that make our the development life easier? If the application is very simple, it is easy. But when the application gets more features, problems will starting popping up. Below is one of the problem we faced in such a scenario.


The application needs to have Facebook login. It is easy to setup that using the Facebook javascript sdk. It worked well when we try this from laptop and the mobile browser. But when the same is tried from native Android wrapper we got an issue. After Facebook login, it ends up in a blank white page. 

The analysis leads to Android WebView limitations. The Facebook login SDK normally creates browser window child window and after login it will close that window and control will be passed to parent window. But when we show the same page using Android WebView control. That javascript popup window closing is not working.


The solution is as follows 
  1. Show the FB login popup in a different WebView control
  2. After the login success, close that window. 
How do we achieve that? Below are the tasks to be done.

Task 1 - Show login popup in different WebView

There is already a WebView in the application. We need to catch the javascript popup show event happened inside the web page and show that popup in a different WebView control. To do that we need to follow steps below
  1. Subclass WebChromeClient and override it's onCreateWindow method. Name it as UriWebChromeClient
  2. From the onCreateWindow method create object of new WebView control and add to the view.
    1. When we create the second WebView control, associate that to our custom WebViewClient which we are going to create in Task 2. That is required to close this second WebView.
  3. The new UriWebChromeClient class object needs to be connected to the existing WebView by calling webViewObj.setWebChromeClient() Method

Task 2 - How to know FB authentication is success to hide WebView

Now we need to think how the Android web view knows whether the FB login is successful. It can only be determined by looking at a particular URL(https://m.facebook.com/v2.0/dialog/oauth) where the FB will be redirecting after login success. How do the Android web view knows that the web redirection happens? It can be done by sub classing WebViewClient class. Steps below
  1. Subclass the WebViewClient class.Name it as UriWebViewClient
  2. Override the onPageFinished() method of WebViewClient in the new inherited UriWebViewClient class and check for the url. If the URL is "https://m.facebook.com/v2.0/dialog/oauth", we can decide that the FB authentication is completed and its time to hide the second WebView.
  3. Override the shouldOverrideUrlLoading() method too and do the similar.
The code is mentioned in this SO link .Only difference from this link is the onPageFinished method overriding.

Reference links


Kostas Karkaletsis said...
This comment has been removed by the author.
Mayank Gupta said...

any example ?

Joymon said...

Hi Mayank,

Sorry to say that right now I don't have that code handy. If you have any public sample repo (Github), I can do some modifications there. Else I will post a sample later.

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