Binding JavaScript code to Android code

Question

Im trying to invoke a method in java from javascript, but this doesn't happen when I run the application in the emulator, the application stops when it is suppose to call the method in java.
here is the java code:

import android.os.Bundle;
import android.webkit.WebView;
import com.phonegap.*;

public class App extends DroidGap {
    WebView webView; 
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        webView = new WebView(this); 
        webView.addJavascriptInterface(new message(), "Show");
        super.loadUrl("file:///android_asset/www/index.html");
    }

    class message {
        String msg() {
            return "Hello World!!";
        }
    }
}

here is the javascript:

<script type="text/javascript">
{
    alert("Start");
    alert(Show.msg());
    alert("End");    
}
</script>

It shows the first alert but nothing thereafter, can anyone help?

Answer 1

Your problem is that you're half using PhoneGap and half not. You're creating a separate WebView class from PhoneGap's. The WebView class that you added "Show" to never gets used. Instead the WebView class that is a member of the super ( DroidGap ) is.

You should do one of two things.

• Use PhoneGap's plugin structure (see examples here )

• Don't use PhoneGap at all and have a class that looks more like the following:

   public class act extends Activity { WebView webView; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); webView = new WebView(this); webView.getSettings().setJavaScriptEnabled(true); // Set JS alert() hook webView.setWebChromeClient(new WebChromeClient() { public boolean onJsAlert(WebView view, String url, String message, JsResult result) { return false; } }); webView.loadUrl("file:///android_asset/www/index.html"); // Add JS libraries webView.addJavascriptInterface(new message(), "Show"); } class message { public String msg() { return "Hello World!!"; } } } 

Note that the method msg needs to be public

Answer 2

Why not just use AlertDialog?

private void showDialog(int title, String message) {
    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.setTitle(title);
    builder.setMessage(message);
    builder.setPositiveButton(R.string.ok_button, new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int id) {
        }
    });
    builder.show();
}