How to safely turn WebView zooming on and off as needed

Question

As mentioned in this unanswered question: WebView throws Receiver not registered: android.widget.ZoomButtonsController

By turning the WebView zoom controls on and off as needed throws this:

java.lang.IllegalArgumentException: Receiver not registered: android.widget.ZoomButtonsController

For some users. I myself have not seen this crash, but I have seen it in the logs coming from devices in the wild. It doesn't happen super frequently, but it is a crash regardless. Any ideas?

Thanks

Update: How to reproduce

I found how to reproduce this crash: http://code.google.com/p/android/issues/detail?id=15694

I'll report back if I discover a workaround.

---

As requested, the full stack trace:

java.lang.IllegalArgumentException: Receiver not registered: android.widget.ZoomButtonsController$1@487a4290
at android.app.ActivityThread$PackageInfo.forgetReceiverDispatcher(ActivityThread.java:793)
at android.app.ContextImpl.unregisterReceiver(ContextImpl.java:913)
at android.content.ContextWrapper.unregisterReceiver(ContextWrapper.java:331)
at android.widget.ZoomButtonsController.setVisible(ZoomButtonsController.java:404)
at android.widget.ZoomButtonsController$2.handleMessage(ZoomButtonsController.java:178)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:4627)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:521)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
at dalvik.system.NativeStart.main(Native Method)

and another similar one:

java.lang.IllegalArgumentException: View not attached to window manager
at android.view.WindowManagerImpl.findViewLocked(WindowManagerImpl.java:391)
at android.view.WindowManagerImpl.removeView(WindowManagerImpl.java:236)
at android.view.Window$LocalWindowManager.removeView(Window.java:432)
at android.widget.ZoomButtonsController.setVisible(ZoomButtonsController.java:406)
at android.widget.ZoomButtonsController$2.handleMessage(ZoomButtonsController.java:178)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:143)
at android.app.ActivityThread.main(ActivityThread.java:5068)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:521)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
at dalvik.system.NativeStart.main(Native Method)

Answer 1

On a Zoom, I found that if one waits for the zoom control to fade out before calling WebView.destroy() a crash no longer occurs. So I've overwritten WebView.destroy() to post a message to a Handler to call WebView.destroy() after a few seconds. From the WebView source we will see the fade-out interval is:

// The time that the Zoom Controls are visible before fading away
private static final long ZOOM_CONTROLS_TIMEOUT =
        ViewConfiguration.getZoomControlsTimeout();

So I used ViewConfiguration.getZoomControlsTimeout() + 1000L as the delay before calling WebView's destroy method. So far no crashes.

Answer 2

If you only want to have pinch zoom working with your webview and you can live without the zoom buttons, you can do this to your webview:

webView.getSettings().setBuiltInZoomControls(true); // will give pinch zoom
webView.getSettings().setDisplayZoomControls(false); // but won't display the zoom buttons

adding

webView.getSettings().setBuiltInZoomControls(true);

in onDestroy / onDestroyView did not help on 3.x.

Answer 3

webView.getSettings().setBuiltInZoomControls(true); did not work for me.

dkneller's suggestion did work, however:

    long timeout = ViewConfiguration.getZoomControlsTimeout();
    new Timer().schedule(new TimerTask() {
        @Override
        public void run() {
            webview.destroy();
        }
    }, timeout);