addJavascriptInterface function doesn't work on API 21

Question

I'm trying to add a javascript interface to a WebView I've found. I followed all the standard tutorial and still getting struggled with the task. When adding the javascript interface, I don't get any exceptions or errors, but when explicitly calling the bridge from JS, I get the following error:

I/chromium: [INFO:CONSOLE(1)] "Uncaught ReferenceError: JSNativeBridge is not defined", source:  (1)

Adding the javascript interface:

new Handler(context.getMainLooper()).post(new Runnable() {
    @Override
    public void run() {
        WebView webView = webViews[0];
        if (Constants.DEBUG_MODE) {
            webView.setWebChromeClient(new WebChromeClient());
            webView.getSettings().setJavaScriptEnabled(true);
        }
        ImpressionSyncJsInterface impressionSyncJsInterface = new ImpressionSyncJsInterface(context);
        webView.addJavascriptInterface(impressionSyncJsInterface, JS_BRIDGE_NAME);
        didAddInterfaceToWebView = true;
    }
});

My interface:

public class ImpressionSyncJsInterface {
    private final Context context;

    public ImpressionSyncJsInterface(Context context) {
        this.context = context;
    }

    @JavascriptInterface
    public void foo() {
        Log.e("TEST", "test");
    }
}

The Javascript execution:

final String javascriptInjectionTest = "javascript: " + JS_BRIDGE_NAME + ".foo();";

new Handler(Looper.getMainLooper()).post(new Runnable() {
    @Override
    public void run() {
        webView.loadUrl(javascriptInjectionTest);
    }
});

Please put the javascript code, from where you are calling java class. — Ashish Rawat
– Ashish Rawat, Commented Jan 25, 2016 at 3:44
I don't see any code loading a page prior to trying to access the injected object. You need to load some page first, see developer.android.com/reference/android/webkit/… — Mikhail Naganov
– Mikhail Naganov, Commented Jan 25, 2016 at 21:44

Daniel · Accepted Answer · 2016-01-26 08:09:44Z

27

Figured out the problem, so I'll share my insights:

The addJavascriptInterface function applies only if called BEFORE a loadUrl / loadData function.

In my case - I expected addJavascriptInterface to inject a JS bridge, but I never reloaded the WebView content, so it was never actively injected.

After reloading the WebView HTML content, the bridge was added as expected.

answered Jan 26, 2016 at 8:09

Daniel

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3 Comments

davidgyoung Over a year ago

You should accept this as your own answer so other folks can find it more easily I just ran into the same thing myself!

CrandellWS Over a year ago

thanks I found it states this in the docs: developer.android.com/reference/android/webkit/… Note that injected objects will not appear in JavaScript until the page is next (re)loaded.

KeitelDOG Over a year ago

Thanks for that answer. The "BEFORE a loadUrl" allowed me to realize that I was adding the interface inside onPageStarted() method of WebViewClient lifecycle, which made it work in some Android phones and not in others. I moved it outside, after webView.setWebViewClient() and before webView.loadUrl().

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