JavaScriptInterface not added on API 18
Question
I am using a WebView to execute some JS code in my app. This works fine so far on my KitKat (targetSdk) device, and also on a 2.2 (minSdk) emulator.
On a 4.3 Nexus 7 I encountered an error though. It seems as the JS object doesn't get injected.
Uncaught ReferenceError: android is not defined at null:1
Following a stripped down version of my code:
public void getData(Context ctx) {
WebView webView = new WebView(ctx);
WebSettings webSettings = webView.getSettings();
webSettings.setJavaScriptEnabled(true);
webView.addJavascriptInterface(new AndroidInterface(), "android");
webView.loadUrl("javascript:console.log(android.getInput());");
}
public class AndroidInterface {
@JavascriptInterface
public String getInput() {
return "FOO";
}
}
The JS itself gets executed fine, so doing console.log('FOO'); prints FOO just as expected. But as soon as I try to access the interface I get the ReferenceError . Any ideas?
Thanks in advance!
2 answers
solution1
1 2014-05-22 09:08:30
Could be a number of things. You can try the following to narrow it down:
- insert a sleep (1sec is more than enough) between the add and the loadUrl. It's unlikely that the API is racey but it's easy to check.
- load a page before calling loadUrl("javascript:..."). Call something like
loadUrl("about:blank")orloadData("<p>foo</p>", ...);and sleep for a bit.
Calling loadUrl("javascript:...") internally evaluates the JavaScript in the current page, it doesn't perform a 'real' navigation. It might be that the interface that you're adding is not being picked up by the context in which your loadUrl("javascript:...") call is executed (especially that the 'starting' page the WebView loads after being constructed is a bit special) and that performing a navigation makes the WebView "pick up" the newly added interface.
solution2
0 2014-05-22 08:16:23
Found a workaround, would still be interesting to know why it doesn't work on 4.3.
So instead of using loadUrl , I surrounded the JS by a piece of HTML and used loadData .
webView.loadData("<!DOCTYPE html><html><head><script type=\"text/javascript\">function go(){console.log(android.getInput());}</script></head><body onload=\"javascript:go()\"></body></html", "text/html", "UTF-8");
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