Android JavascriptInterface use context to call method in activity (OOP)

Question

In OOP, I can use the object to call its methods. So I want to do that in android using the same concept. However, it doesn't work. I used context to call the function updateLvl(int), but it said the method cannot be resolved. I want to know how can I use the context to call the method updateLvl?

public class MainActivity extends Activity {

private WebView webview;
SharedPreferences sharedPref;
SharedPreferences.Editor editor;

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);


    sharedPref = this.getPreferences(0);
    editor = sharedPref.edit();

    webview = new WebView(this);
    webview.getSettings().setJavaScriptEnabled(true);
    webview.addJavascriptInterface(new WebViewJavaScriptInterface2(this), "app");


public void updateLvl(int newLvl){
    sharedPref = this.getPreferences(0);
    editor = sharedPref.edit();
    int be4Level = sharedPref.getInt("currLevel", 1);
    if (newLvl >= be4Level){
        editor.putInt("currLevel", newLvl);
        editor.commit();
    }
  }


}

class WebViewJavaScriptInterface2{

private Context context;
/*
 * Need a reference to the context in order to sent a post message
 */
public WebViewJavaScriptInterface2(Context context){
    this.context = context;
}

@JavascriptInterface
public void openLvl(int lvl){
    context.updateLvl(lvl);
}

}

Pavneet_Singh · Accepted Answer · 2017-06-24 17:41:39Z

5

you need to cast your context as MainActivity because your MainActivity class has updateLvl method not Context class hence compiler will show you error while applying static binding

@JavascriptInterface
public void openLvl(int lvl){
    if(context instanceof MainActivity) // add safety check if required
        ((MainActivity)context).updateLvl(lvl);
}

edited Jun 24, 2017 at 17:41

answered Jun 24, 2017 at 17:27

Pavneet_Singh

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Comments

stamanuel · Accepted Answer · 2017-06-24 17:31:37Z

1

The Context is not the instance of your WebViewJavaScriptInterface2 but a class of the android system (as well as Activity).

One way is to cast the context to the activity as Pavneet suggested. But this has the flaw that you can not be absolutely sure in your WebViewJavaScriptInterface2 that is is instanced from the right activity. Also you can use it just from one activity if you cast it to that one.

A cleaner way would be to define a callback interface, implement that interface in your activity (or multiple activity) and pass that callback interface into the WebViewJavaScriptInterface2.

answered Jun 24, 2017 at 17:31

stamanuel

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Comments

Jeremy Caney · Accepted Answer · 2020-06-30 18:22:11Z

0

This might help someone.

new Handler(Looper.getMainLooper())
  .post(new Runnable(){
    @override
    public void run(){
      updateLvl(lvl);
    }
  });

edited Jun 30, 2020 at 18:22

Jeremy Caney

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answered Jun 30, 2020 at 14:59

Dbs ray

1

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