Why does Android WebView reset JavaScript context on second page load?

Question

I am using an Android WebView with local data by first setting up a JavaScript environment and then loading web content that relies on the existence of the JavaScript environment:

test.js:

alert("test.js: type of window.myVar is: " + (typeof window.myVar));
window.myVar = {};

test.html:

<!DOCTYPE>
<html><head>
<script>
alert("test.html: type of window.myVar is: " + (typeof window.myVar));
</script>
</head><body></body></html>

loading procedure in Java:

private void loadData() {
    _webView.loadUrl("javascript:" + testJSContent);
    _webView.loadDataWithBaseURL(null, testHTMLContent, "text/html", "utf-8", null);
}

The first time loadData() is triggered, window.myVar is available from the loaded HTML page, but undefined on any subsequent tries. Here is the alert output on three invokations:

-> loadData() called
"test.js: type of window.myVar is: undefined"
"test.html: type of window.myVar is: object"
-> loadData() called
"test.js: type of window.myVar is: object"
"test.html: type of window.myVar is: undefined"
-> loadData() called
"test.js: type of window.myVar is: undefined"
"test.html: type of window.myVar is: undefined"

Any ideas why the JavaScript object created by injection is only persistent until the second page load?

Thanks for any help!

afaik, every page loaded has its own javascript variables. If it wouldn't be like this, you could do XXS within your browser history...! it's not a matter of android-webview javascript in general, but maybe I misunderstood the problem — lelloman
Good point indeed. But since setting up a JS context like this works for the first page load, do you know if there is any way to reset the WebView back to the initial state and re-enable JS injection? — user2174643
something like myWebView.goBack()? I don't understand why you need to put javascript and html in two separated steps — lelloman
This procedure is used within an Android SDK library where in-SDK JavaScript code has to be included into HTML markup retrieved from an external server. — user2174643
I still don't understand the need of loading content (js, html or whatever) two times...can't you just merge them and load just once? — lelloman

greenapps greenapps · Accepted Answer · 2013-03-15T22:28:28

You should first load the html and after that page has fully loaded inject the javascript. Do it in OnPageFinished of the WebViewClient.

Why does Android WebView reset JavaScript context on second page load?

1 Answers