Question

I have webview, and I’m using geo-location feature in android.
I’m using javascript (onload) to call Android method

public void getLocation() {
   _context.getLocation();
}

and when location recieved this execute

public void locationUpdated(Location location) {
        NumberFormat frm = NumberFormat.getNumberInstance(new Locale("en_US"));
        // call javascript function
        webView.loadUrl("javascript:locationChangedHandler(" + frm.format (location.getLatitude()) + "," + frm.format(location.getLongitude()) + ")");
}

Sometime I got this exception, and this exception

04-04 01:17:06.262: ERROR/AndroidRuntime(659): FATAL EXCEPTION: Timer-1
        android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
        at android.view.ViewRoot.checkThread(ViewRoot.java:2802)
        at android.view.ViewRoot.invalidateChild(ViewRoot.java:607)
        at android.view.ViewRoot.invalidateChildInParent(ViewRoot.java:633)
        at android.view.ViewGroup.invalidateChild(ViewGroup.java:2505)
        at android.view.View.invalidate(View.java:5139)
        at android.view.View.onFocusChanged(View.java:2664)
        at android.widget.TextView.onFocusChanged(TextView.java:6469)
        at android.widget.AutoCompleteTextView.onFocusChanged(AutoCompleteTextView.java:1048)
        at android.webkit.WebTextView.onFocusChanged(WebTextView.java:357)
        at android.view.View.clearFocusForRemoval(View.java:2577)
        at android.view.ViewGroup.removeViewInternal(ViewGroup.java:2188)
        at android.view.ViewGroup.removeViewInternal(ViewGroup.java:2181)
        at android.view.ViewGroup.removeView(ViewGroup.java:2129)
        at android.webkit.WebTextView.remove(WebTextView.java:583)
        at android.webkit.WebView.clearTextEntry(WebView.java:1830)
        at android.webkit.WebView.loadUrl(WebView.java:1542)
        at android.webkit.WebView.loadUrl(WebView.java:1553)
        at com.binus.MainView$1.gotLocation(MainView.java:33)
        at com.binus.GeoLocation$GetLastLocation.run(GeoLocation.java:88)
        at java.util.Timer$TimerImpl.run(Timer.java:289)

Is this something todo with accessing UI thread from other thread ?
Is calling Android (Java) method from Javascript execute on non UI thread ?

And how to make my code thread safe ?

Answer 1

I’m not sure how you got off the UI thread, but to get back on you can use post:

public void locationUpdated(final Location location) {
    post(new Runnable() {
        @Override
        public void run() {
            webView.loadUrl(...);
        }
    });
}

if you’re inside a View. If you’re in an Activity then change post to runOnUiThread.