Javascript Interface, error "Uncaught Error: Error calling method on NPObject"

Question

In my Android application, I am using the WebAppInterface to bridge from Javascript to Java.

My .html file includes some JS that runs "Android.canPlay();" at certain times.

In my app, the function "canPlay()" fires a variable listener.

When the variable listener fires, if conditions are met, some files are renamed (temporary files, that were downloaded with a .tmp additional extension, including the .html file (so it is .html.tmp, with the original .html existing alongside it))

After the renaming happens, the Web View is reloaded (I have tried using both a function and just ".loadUrl()" - both give errors)

When time comes to reload the html file in the webview, I get the error:

E/Web Console﹕ Uncaught Error: Error calling method on NPObject. at file:////mnt/sdcard/Download/qwerty/playlists/29/2/index.html:206

Line 206 is the "Android.canPlay()" call.

Things to note - If I don't rename the files before reloading the webview and instead, rename then from a background service that runs, I don't have this error (although I do get one about running stuff on the WebViewCoreThread)

Some code:

WebAppInterface

public class WebAppInterface {
    final Context mContext;

    WebAppInterface(Context c) {
        mContext = c;
    }

    @JavascriptInterface
    public void canPlay()
    {
        mPlaylistReady.changeState(true);
    }
}

Variable Listener (gets fired via a listener class) (some bits of code removed e.g. sharedprefences for file locations)

@Override
public void onStateChange(boolean state) {

    if (state) { // true
            // this finds all the files and removes the .tmp extension
            fileRenamer.removeTmp(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS + "/qwerty/playlists/"));

            // reloads the webview
            WebViewActivity.this.runOnUiThread(new Runnable() {
                public void run() {
                    webView.loadUrl("file:///" + htmlFile.getAbsolutePath());
                }
            });

        }
    }
}

FileRenamer class

public class FileRenamer {

    public void removeTmp(File directory)
    {
        File dir = directory;
        if(dir.isDirectory()) {
            for(File child : dir.listFiles()) {
                String name = child.getName();
                String ext = name.substring(name.lastIndexOf('.'));
                if(ext.equals(".tmp")) {
                    final int lastPeriodPos = name.lastIndexOf('.');
                    File renamed = new File(dir, name.substring(0, lastPeriodPos));
                    child.renameTo(renamed);
                }
            }
        }
    }

}

Answer 1

This error is thrown by JavaScript because an exception has occurred during the Java canPlay() implementation.

Try to encapsulate the WebAppInterface.canPlay() method in a try-catch clause and log the exception to find out what could've been happening.

Besides that, I'm trying to discover a way to map exceptions in the JavaScript context, but i'm afraid that is not possible.