The method findViewById(int) is undefined for the type new Runnable(){}

Question

I'm working on making a Phonegap plugin for Android. When I add the findViewById method to this.ctx.runOnUiThread(new Runnable() I get an error as stated in the title.

Here is my code:

package com.company.msgbox;


import java.io.File;

import org.crossplatform.phonegap.trial.alternativeTo.R;
import org.json.JSONArray;
import org.json.JSONException;

import android.app.AlertDialog;
import android.graphics.Bitmap;
import android.view.View;

import com.phonegap.api.Plugin;
import com.phonegap.api.PluginResult;
import com.phonegap.api.PluginResult.Status;

public class msgbox extends Plugin {

    private static final String SHOW = "show";
    private static final int MSG_INDEX = 0;
    private String msg;

    @Override
    public PluginResult execute(String arg0, final JSONArray arg1, String arg2) {
        if ( arg0.equals(SHOW) ) {
            this.ctx.runOnUiThread(new Runnable() {
                public void run() {
                    // try/catch generated by editor
                    try {
                        msg = arg1.getString(MSG_INDEX);
                    } catch (JSONException e) {
                       // TODO Auto-generated catch block
                       e.printStackTrace();
                    }

                    AlertDialog alertDialog = new AlertDialog.Builder(ctx).create();
                    alertDialog.setTitle("Title");
                    alertDialog.setMessage(msg);
                    alertDialog.show();

                    View content = findViewById(R.id.layoutroot);
                    Bitmap bitmap = content.getDrawingCache();
                    File file = new File("/sdcard/test.png");
                }
            });
        }

        return new PluginResult(Status.OK);
    }

}

Solution

You need to call findViewById from a class that actually has the method. The good practice is usually to pass around the Activity you're creating this class from. Something like:

public class msgbox extends Plugin {
    private static final String SHOW = "show";
    private static final int MSG_INDEX = 0;
    private String msg;
    private final Activity parent;

    // constructor
    public msgbox(Activity parent) {
        this.parent = parent;
    }

Then you can do a:

parent.findViewById(R.id.layoutroot)

You construct your msgbox from within an activity by using:

msgbox myMsgBox = new msgbox(this);

Of course, to do that, the R.id.layoutroot component must be in the activity you passed.

If you're not in an activity when you construct the msgbox, you can replace the constructor injection with a setter:

public void setParent(Activity parent) {
    this.parent = parent;
}

Although, to be able to use findViewById within your Runnable, parent needs to be final, so you'll have to copy it to a final variable (setter injection cannot be final, obviously)

(NB: Also, your class doesn't use standard java naming conventions, it's confusing: call it MsgBox)