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
– Ilya Luzyanin, Commented Aug 10, 2014 at 19:33
You mean: b.Click += delegate { int j = i; processClick(j); }; ? I've tried that and it didn't work. — Vilda
– Vilda, Commented Aug 10, 2014 at 19:33

Community · Accepted Answer · 2017-05-23 12:24:09Z

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, 2017 at 12:24

CommunityBot

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answered Aug 10, 2014 at 19:35

Ilya Luzyanin

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5 Comments

Vilda Over a year ago

I did and it still doesn't work. It still logs number 3;

Vilda Over a year ago

Sorry, my bad. I put the var j = i; in the delegate. Solved. Thanks.

Vilda Over a year ago

That's my plan, but I can do that in 8 minutes.

Ilya Luzyanin Over a year ago

Oh, sorry, didn't know about the limit :) Good luck!

Jeroen Vannevel Over a year ago

Could you elaborate on the issue (e.g. 'closure') or at least provide references to good reading material?

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