I'm using VS 2005 C# Express.

I have an event handler that is called when the text cursor leaves one of many different text boxes.
When this is called, I want the text colour in that text box to change to Red. I assume that the
"sender" argument in the call is the text box that triggered the event. When I tried to change the
text colour using sender.ForeColor = System.Drawing.Color.Red; I get a compile error: 'object' does
not contain a definition for 'BackColor'. This didn't surprise me since I'm a C# beginner. Is there
some sort of cast I can use to make it work, or do I have to use if... else if... etc statements to
check for each of the text boxes that might have triggered the event (eg one is called tbxFbeg)?
Here's a fragment of my code...

private void tbxSettingsSa_Leave(object sender, EventArgs e){
sender.ForeColor = System.Drawing.Color.Red; //get compile error: 'object' does not contain a
definition for 'BackColor'
// sender is a textbox. The following line works OK...
// tbxFbeg.ForeColor = System.Drawing.Color.Red;
}

Yep; a straight cast... for bullet-proofing I'll illustrate the case
where you *hope* is is a textbox, but aren't sure...

TextBox tb = sender as TextBox;
if(tb!=null) { // sender was (as expected) a TextBox
tb.ForeColor =System.Color.Red;
}

Of course, if your handler only ever deals with a single control, you
can code directly against the field (as per your "this works"
example).

Marc

You need to cast the object first.

TextBox myTextBox = (TextBox)sender;

/Niklas

Jay skrev:

> I'm using VS 2005 C# Express.
>
> I have an event handler that is called when the text cursor leaves one of many different text boxes.
> When this is called, I want the text colour in that text box to change to Red. I assume that the
> "sender" argument in the call is the text box that triggered the event. When I tried to change the
> text colour using sender.ForeColor = System.Drawing.Color.Red; I get a compile error: 'object' does
> not contain a definition for 'BackColor'. This didn't surprise me since I'm a C# beginner. Is there
> some sort of cast I can use to make it work, or do I have to use if... else if... etc statements to
> check for each of the text boxes that might have triggered the event (eg one is called tbxFbeg)?
> Here's a fragment of my code...
>
> private void tbxSettingsSa_Leave(object sender, EventArgs e){
> sender.ForeColor = System.Drawing.Color.Red; //get compile error: 'object' does not contain a
> definition for 'BackColor'
> // sender is a textbox. The following line works OK...
> // tbxFbeg.ForeColor = System.Drawing.Color.Red;
> }

Thanks Marc + Niklas for your replies. It now works.

I've also found that this works, which is a little more compact. I assume it's just as good, but do
say if it isn't (I know for sure that it is always a textbox).

((TextBox)sender).ForeColor = System.Drawing.Color.Red;

Jay


"Jay" <nospam> wrote in message news:OChsp%(E-Mail Removed)...
I'm using VS 2005 C# Express.

I have an event handler that is called when the text cursor leaves one of many different text boxes.
When this is called, I want the text colour in that text box to change to Red. I assume that the
"sender" argument in the call is the text box that triggered the event. When I tried to change the
text colour using sender.ForeColor = System.Drawing.Color.Red; I get a compile error: 'object' does
not contain a definition for 'BackColor'. This didn't surprise me since I'm a C# beginner. Is there
some sort of cast I can use to make it work, or do I have to use if... else if... etc statements to
check for each of the text boxes that might have triggered the event (eg one is called tbxFbeg)?
Here's a fragment of my code...

private void tbxSettingsSa_Leave(object sender, EventArgs e){
sender.ForeColor = System.Drawing.Color.Red; //get compile error: 'object' does not contain a
definition for 'BackColor'
// sender is a textbox. The following line works OK...
// tbxFbeg.ForeColor = System.Drawing.Color.Red;
}

Then yes, that is absolutely fine. The variable approach is useful
when you want to apply more than one operation to the same object -
i.e. set a few properties rather than just one. Otherwise you need to
cast each time, or create a wrapper method (and cast the parameter to
the method).

Marc

Thanks again for your help.

Jay

"Marc Gravell" <(E-Mail Removed)> wrote in message
news:%(E-Mail Removed)...
Then yes, that is absolutely fine. The variable approach is useful
when you want to apply more than one operation to the same object -
i.e. set a few properties rather than just one. Otherwise you need to
cast each time, or create a wrapper method (and cast the parameter to
the method).

Marc

Dale <(E-Mail Removed)> wrote:
> I agree with Marc's initial recommendation. You should do the type checking
> that the "as" statement does and then check for null.

That depends on whether it not being a TextBox will always mean there's
a coding error. If it does, the exception generated from the failed
cast is entirely appropriate - using "as" would mask the error.

I only use "as" when the cast could legitimately fail in a non-error
case.

--
Jon Skeet - <(E-Mail Removed)>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too