Sometimes throws Uncaught Error: Error calling method on NPObject on Android

Question

I am having problems with the Webview in Android and it\'s JavascriptInterfaces.

I am passing a string to the JavascriptInterface. When debugging it, I receive the c

Answer 1

Another reason can be a RuntimeException on a WebViewCoreThread. Any exception occurred after receiving @JavascriptInterface call will be logged as NPObject error if still running on a WebView thread. Overall insufficient trace message with little clue about the problem.

Correct your issue with handling javascript interface call on a suitable thread.

Example A. (NPObject error):

@JavascriptInterface
public void jsCall() {
    Log.v(TAG, "Prepared NullPointerException on "+Thread.currentThread());
    String s = null;
    s.length();  // This will cause NPObject error
}

Example B. (NullPointerException):

@JavascriptInterface
public void jsCall() {
    new Thread(new Runnable() {
        @Override
        public void run() {
            Log.v(TAG, "Prepared NullPointerException on " + Thread.currentThread());
            String s = null;
            s.length();  // This will throw NullPointerException
        }
    }).start();
}

Take this as an addition to @Nico.S's answer.