Android Xamarin programmatically generated Button Click

Question

I am creating buttons programmatically in Android Xamarin (C#) like this:

for(int i = 0; i < 3; i++) {
    ...
    Button b = new Button(this);
    b.Click += delegate {
        processClick(i);
    };
    ...
}

the processClick method looks like this:

public void processClick(int i) {
    ... Log("i: " + i);
}

It successfully creates 3 buttons, but if I press any of them, the console log's number 3. The question is, how handle clicked events of programmatically created buttons?

Classical closures. Use `var j= i;` inside for-loop and use `processClick(j);` — Ilya Luzyanin, Aug 10 '14 at 19:33
You mean: b.Click += delegate { int j = i; processClick(j); }; ? I've tried that and it didn't work. — Vilda, Aug 10 '14 at 19:33

score 4 · Accepted Answer · edited May 23 '17 at 12:24

4

This is called closure. Rewrite your for loop as follows:

for(int i = 0; i < 3; i++) {
    ...
    Button b = new Button(this);
    var j= i;
    b.Click += delegate {
        processClick(j);
    };
    ...
}

Also there is a good discussion on SO related to this topic.

edited May 23 '17 at 12:24

Community

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answered Aug 10 '14 at 19:35

Ilya Luzyanin

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I did and it still doesn't work. It still logs number 3; – Vilda Aug 10 '14 at 19:36
Sorry, my bad. I put the var j = i; in the delegate. Solved. Thanks. – Vilda Aug 10 '14 at 19:37
That's my plan, but I can do that in 8 minutes. – Vilda Aug 10 '14 at 19:39
Oh, sorry, didn't know about the limit :) Good luck! – Ilya Luzyanin Aug 10 '14 at 19:40
Could you elaborate on the issue (e.g. 'closure') or at least provide references to good reading material? – Jeroen Vannevel Aug 10 '14 at 19:41

Android Xamarin programmatically generated Button Click

1 Answers1