CODEWITHSUNDEEP
javaandroid
BenH
BenH

Reputation: 2120

I want to refer to a non-final variable inside an inner class defined in a different method

I'm writing an Android app, in which I have several buttons laid out in a grid. I want to set the onClick method of each button, so I wrote this:

for (int i = 0; i < button.length; i++) {
    for (int j = 0; j < button[0].length; j++) {
        button[i][j].setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                press(i, j);
            }
        });
    }
}

where press(int i, int j) is implemented elsewhere. I get the error, "Cannot refer to a non-final variable i inside an inner class defined in a different method".

So, right now I just have each function written out, like this:

button[0][0].setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {
        press(0, 0);
    }
});

button[0][1].setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {
        press(0, 1);
    }
});

// more like this...

This works, but it seems silly. Is there a better way?

Upvotes: 4

Views: 1917

Answers (6)

Huang
Huang

Reputation: 4842

Declare i and j as global variable in the outer class

Upvotes: 1

Ray Tayek
Ray Tayek

Reputation: 10003

you can get by with one listener:

package tayek.so9551773;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.*;
import android.util.Log;
public class So9551773 extends Activity {
    void press(int i,int j) {
        Log.d("so",i+","+j+" was clicked");
        System.out.println(i+","+j+" was clicked");
    }
    void addButtons(TableLayout tableLayout) {
        for(int i=0;i<buttons.length;i++) {
            TableRow tableRow=new TableRow(this);
            tableLayout.addView(tableRow);
            for(int j=0;j<buttons[i].length;j++) {
                buttons[i][j]=new Button(this);
                tableRow.addView(buttons[i][j]);
                buttons[i][j].setText(i+" "+j);
                buttons[i][j].setId(i*buttons.length+j);
                buttons[i][j].setOnClickListener(onClickListener);
            }
        }
    }
    @Override public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d("so","created");
        TableLayout tableLayout=new TableLayout(this);
        addButtons(tableLayout);
        setContentView(tableLayout);
    }
    Button[][] buttons=new Button[3][3];
    OnClickListener onClickListener=new OnClickListener(){
        public void onClick(View v) {
            int id=v.getId();
            press(id/buttons.length,id%buttons.length);
        }
    };
}

Upvotes: 1

jacobm
jacobm

Reputation: 14025

for (int i = 0; i < button.length; i++) {
    for (int j = 0; j < button[0].length; j++) {

        final int localI = i;
        final int localJ = j;

        button[localI][localJ].setOnClickListener(...);
    }
}

Upvotes: 2

Vojislav Stojkovic
Vojislav Stojkovic

Reputation: 8153

Yes, try this:

for (int i = 0; i < button.length; i++) {
    for (int j = 0; j < button[0].length; j++) {
        final int listenerI = i;
        final int listenerJ = j;
        button[i][j].setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                press(listenerI, listenerJ);
            }
        });
    }
}

Upvotes: 6

Adam Zalcman
Adam Zalcman

Reputation: 27233

You can define a helper method to set the listener for a button:

private static void setListenerForButton(Button button, final int i, final int j) {
    button.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            press(i, j);
        }
    });
}

and then you can use it like this

for (int i = 0; i < button.length; i++) {
    for (int j = 0; j < button[0].length; j++) {
        setListenerForButton(button[i][j], i, j);
    }
}

This is a special case of a more general solution: define extra final int variables for use in the inner class and initialize them with the values of i and j. In this case the extra final int variables are arguments to the helper function.

Upvotes: 4

paulsm4
paulsm4

Reputation: 121649

You can easily do something like that in Javascript ... but not Java :)

Here are a couple of good links:

Upvotes: 0

Related Questions