WebView methods on same thread error

Issue

I have a android program (Java + html in a webview). I can call from the javascript to the Java code. But the other way around stopped working (after updating in eclipse).

So this is what I’m trying to do

  • Make a webview (worked)
  • calling in javascript to AndroidFunction.test(); (worked)
  • the java test() function call webView.loadUrl(“javascript:helloBack()”); (! not working anymore)

I tried to let it work with the WebView in the MainActivity, but it didnt work.

MainActivity.java

public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        final WebView webView  (WebView)findViewById(R.id.webView);
        webView.getSettings().setJavaScriptEnabled(true);
        webView.setWebChromeClient(new WebChromeClient());
        WebSettings webSettings  webView.getSettings();
        webSettings.setJavaScriptEnabled(true);

        javascr  new Javascript(this, webView);
        webView.addJavascriptInterface(javascr, "AndroidFunction");
        webView.loadUrl("file:///android_asset/www/index.html");

        ....
}

Javascript.java

public class Javascript {   
    Context cont;
    WebView webView;

    Javascript(Context c, WebView w) {
        cont  c;
        webView  w;
    }

    // function called in the javascript by AndroidFunction.test();
    public void test() {
          // Breaking point!!!
        webView.loadUrl("javascript:helloBack()");
    }

Error:

03-24 11:47:50.103: W/WebView(21026):   at com.android.org.chromium.base.SystemMessageHandler.handleMessage(SystemMessageHandler.java:27)
03-24 11:47:50.103: W/WebView(21026):   java.lang.Throwable: A WebView method was called on thread 'JavaBridge'. All WebView methods must be called on the same thread. (Expected Looper Looper{41ab68f8} called on Looper{41bb70a8}, FYI main Looper is Looper{41ab68f8})

03-24 11:47:50.103: W/WebView(21026):   at android.webkit.WebView.checkThread(WebView.java:2063)
03-24 11:47:50.103: W/WebView(21026):   at android.webkit.WebView.loadUrl(WebView.java:794)
03-24 11:47:50.103: W/WebView(21026):   at com.example.hellobt.Javascript.test(Javascript.java:24)

03-24 11:47:50.103: W/WebView(21026):   at com.android.org.chromium.base.SystemMessageHandler.nativeDoRunLoopOnce(Native Method)
03-24 11:47:50.103: W/WebView(21026):   at com.android.org.chromium.base.SystemMessageHandler.handleMessage(SystemMessageHandler.java:27)
03-24 11:47:50.103: W/WebView(21026):   at android.os.Handler.dispatchMessage(Handler.java:102)

03-24 11:47:50.103: W/WebView(21026):   at android.os.Looper.loop(Looper.java:137)
03-24 11:47:50.103: W/WebView(21026):   at android.os.HandlerThread.run(HandlerThread.java:61)

Thanks for the answer. I edited the function in my Javascript file like this:

private void test(final String s) {
        webView.post(new Runnable() {
            public void run() {
                webView.loadUrl("javascript:" + s + ";");
            }
        });
        System.out.println("javscript done..");
    }

Solution

The JavaScript method is executed on a background (i.e. non-UI) thread. You need to call all Android View related methods on the UI thread. You can achieve what you need with:

mWebView.post(new Runnable() {
    @Override
    public void run() {
        mWebView.loadUrl(...).
    }
});

Which will post the task to run on the UI thread.

Answered By – ksasq

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