How to refer to a dynamically created control in event handler?

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gnewsgroup - 19 Feb 2008 20:21 GMT

Suppose I create a button on the fly and assign an event handler to it
in the code-behind like so:

protected Button CreateMyButton()
{
Button myButton = new Button();
myButton.Text = "Test";
myButton.Click += new EventHandler(myButton_Click);
return myButton;
}

Now, in myButton_Click event handler, how do I get a reference to the
newly created Button object called myButton?

In the Click event handler, we cannot directly say something like

myButton.Text = "Text has changed";

which I tried, and for which I got this:

System.NullReferenceException: Object reference not set to an instance
of an object.

I got the same exception even if I declared myButton as a class-level
private member.

So here is the question: How to refer to a dynamically created control
in the event handler?

Thank you.

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bruce barker - 19 Feb 2008 20:55 GMT

two options

1) make Button myButton a class variable instead of a local, which is how
the aspx page does it.

2) the first arg to the event handler is the object (button) that caused the
event. just cast it as a Button

-- bruce (sqlwork.com)

> Suppose I create a button on the fly and assign an event handler to it
> in the code-behind like so:
[quoted text clipped - 26 lines]
>
> Thank you.

Reply to this Message

Scott Roberts - 19 Feb 2008 20:57 GMT

> Suppose I create a button on the fly and assign an event handler to it
> in the code-behind like so:
[quoted text clipped - 24 lines]
> So here is the question: How to refer to a dynamically created control
> in the event handler?

The "sender" parameter is the control that generated the event. You'll need
to cast it to a Button.

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gnewsgroup - 19 Feb 2008 21:26 GMT

On Feb 19, 3:57 pm, "Scott Roberts" <srobe...@no.spam.here-webworks-
software.com> wrote:

> > Suppose I create a button on the fly and assign an event handler to it
> > in the code-behind like so:
[quoted text clipped - 29 lines]
>
> - Show quoted text -

Thank both of you. I was tring to see what methods intellisense would
show me while I typed up sender dot. But none of those seemed to be
helpful.

Now that I realize that I can cast the sender object to the type of
the object which raised the event, I also realize that I might have
simplified my question.

I am actually using Dundas to create some charts on the fly. For
example, I create Chart1 on the fly and put it in a placeholder. In
the Dundas GanttChart example, there is a Chart1_PostPaint event
handler which draws stuff on the chart *after* the chart has been
rendered (my understanding). The example code goes like this:

private void Chart1_PostPaint(object sender,
Dundas.Charting.WebControl.ChartPaintEventArgs e)
{
if(sender is ChartArea)
{
Series series = Chart1.Series["Tasks"];
// [snip]
}
}

Note that in their example, this Chart1 is declared in the aspx file.
The problem for me is that whereas the *sender* is ChartArea, they are
referring to Chart1, which is not a ChartArea, but some kind of parent
of ChartArea. I can't seem to get a reference to the parent from the
*sender* ChartArea. That's why I got stuck.

Mark: I did try declaring Chart1 as a class-level private member, but
it did not help.

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gnewsgroup - 19 Feb 2008 21:38 GMT

> On Feb 19, 3:57 pm, "Scott Roberts" <srobe...@no.spam.here-webworks-
>
[quoted text clipped - 72 lines]
>
> - Show quoted text -

I had a method that returns the newly-created chart, now I declare
Chart1 as private member, and the method is changed to return void and
keeps updating chart1 contents and then in the PostPaoint event, I
refer to it as this.Chart1. It works! I didn't think it through.
Thanks for Mark!

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How to refer to a dynamically created control in event handler?

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