AndroidLocalStorage

LocalStorage is partially broken in Android webviews : Local storage is supposed to be a persistent storage available accros all tabs (or windows) of a browser. On Android, LocalStorage works well but only in the current webview. Multiple webviews of the same app can't share the same data with LocalStorage. That is sad !

JavaScriptInterface to the rescue !

This sample Android app shows you how you can fix the webview LocalStorage with a JavaScriptInterface.

What we do here is :

• Create an Android database with a simple key/value table
• Create a JavaScriptInterface which implements all LocalStorage's methods (getItem, setItem, removeItem, clear)
• Add it to the webview
• Replace the JavaScript LocalStorage with this "new one" so that you don't have to change the way you use your localStorage usually.

How to use it in your own project ?

• Include the LocalStorage.java
• Create the JavaScriptInterface and add it to the webview as shown in MainFragment.java
• Bind the JavaScript LocalStorage to the new one as shown in assets/index.html

This last step is as simple as this :

<script type="text/javascript">
        try{
            //we replace default localStorage with our Android Database one
            window.localStorage=LocalStorage;    
        }catch(e){
            //LocalStorage class was not found. be sure to add it to the webview
		         	alert("LocalStorage ERROR : can't find android class LocalStorage. switching to raw localStorage")		        
		      }
    //then use your localStorage as usual
    localStorage.setItem('foo','it works')
    alert(localStorage.getItem('foo'))
    
</script>

Play with this example project to see how it works.