EventArgs that return values... How do i replicate?

[Michael.Suarez]

Consider the TextBox Control. It has a KeyPress event of type
KeyPressEventHa ndler which passes a KeyPressEventAr gs to whatever
method is assigned to the event.

When you set e.Handled = false within the assigned method, it disallows
the keypress.

Suppose I have a usercontrol consisting of a textbox, a button, and a
listview. When the user enters something in the textbox and clicks the
button, the textbox's text gets added to the listview as a new item.

Suppose I want to create an event that gets invoked on the button
click, called BeforeAddTextTo Listview, which will be of type
BeforeAddTextTo ListviewHandler and pass
BeforeAddTextTo ListviewEventAr gs to whatever method is assigned to the
event.

Suppose BeforeAddTextTo ListviewEventAr gs has a property called Allowed.
When Allowed=true, the addition to the listview will occur.

This gives the user of the usercontrol the ability to control what is
allowed to go into the listview.

So in my the usercontrols class I have:

public event BeforeAddTextTo ListviewHandler BeforeAddTextTo Listview;

public delegate void BeforeAddTextTo ListviewHandler (object sender,
BeforeAddTextTo ListviewEventAr gs e);

private void btnAddTextToLis tView_Click(obj ect sender, EventArgs e)
{

BeforeAddTextTo ListviewEventAr gs e = new
BeforeAddTextTo ListviewEventAr gs();

if (BeforeAddTextT oListview!= null)
{
BeforeAddTextTo Listview(this, e);
}

if (e.Allowed)
{
//add text to listview
}

}

The problem here is that e is not passed by reference, so it wont know
the value of allowed set by the user.

I could just define BeforeAddTextTo ListviewHandler as:

public delegate void BeforeAddTextTo ListviewHandler (object sender, ref
BeforeAddTextTo ListviewEventAr gs e);

and pass e by reference. Then I would get what i want.

However, the KeyPressEventAr gs in KeyPressEventHa ndler is not passed
by reference.

So what I want to know and what i want to do is...
How does the KeyPressEventHa ndler get the e.Handled back when e does
not have the ref keyword preceding it?
How can i replicate this?

Any help, comments, suggestions greatly appreciated.

Thanks,
Mike

[Michael.Suarez]

nevermind...

I tried it without the ref and it worked, so I just answered my own
question.... for some reason i thought it wouldn't.

I guess the ref is assumed when you are dealing with eventhandlers.

Mi************@ gmail.com wrote:

Consider the TextBox Control. It has a KeyPress event of type
KeyPressEventHa ndler which passes a KeyPressEventAr gs to whatever
method is assigned to the event.

When you set e.Handled = false within the assigned method, it disallows
the keypress.

Suppose I have a usercontrol consisting of a textbox, a button, and a
listview. When the user enters something in the textbox and clicks the
button, the textbox's text gets added to the listview as a new item.

Suppose I want to create an event that gets invoked on the button
click, called BeforeAddTextTo Listview, which will be of type
BeforeAddTextTo ListviewHandler and pass
BeforeAddTextTo ListviewEventAr gs to whatever method is assigned to the
event.

Suppose BeforeAddTextTo ListviewEventAr gs has a property called Allowed.
When Allowed=true, the addition to the listview will occur.

This gives the user of the usercontrol the ability to control what is
allowed to go into the listview.

So in my the usercontrols class I have:

public event BeforeAddTextTo ListviewHandler BeforeAddTextTo Listview;

public delegate void BeforeAddTextTo ListviewHandler (object sender,
BeforeAddTextTo ListviewEventAr gs e);

private void btnAddTextToLis tView_Click(obj ect sender, EventArgs e)
{

BeforeAddTextTo ListviewEventAr gs e = new
BeforeAddTextTo ListviewEventAr gs();

if (BeforeAddTextT oListview!= null)
{
BeforeAddTextTo Listview(this, e);
}

if (e.Allowed)
{
//add text to listview
}

}

The problem here is that e is not passed by reference, so it wont know
the value of allowed set by the user.

I could just define BeforeAddTextTo ListviewHandler as:

public delegate void BeforeAddTextTo ListviewHandler (object sender, ref
BeforeAddTextTo ListviewEventAr gs e);

and pass e by reference. Then I would get what i want.

However, the KeyPressEventAr gs in KeyPressEventHa ndler is not passed
by reference.

So what I want to know and what i want to do is...
How does the KeyPressEventHa ndler get the e.Handled back when e does
not have the ref keyword preceding it?
How can i replicate this?

Any help, comments, suggestions greatly appreciated.

Thanks,
Mike

[Brian Gideon]

Michael,

I think you may be a little confused about value and reference types
and how they behave with the different parameter passing mechanisms.
Maybe the following article will help clear things up.

http://www.yoda.arachsys.com/csharp/parameters.html

Brian

Mi************@ gmail.com wrote:

nevermind...

I tried it without the ref and it worked, so I just answered my own
question.... for some reason i thought it wouldn't.

I guess the ref is assumed when you are dealing with eventhandlers.

[Michael.Suarez]

thanks.

Brian Gideon wrote:

Michael,

I think you may be a little confused about value and reference types
and how they behave with the different parameter passing mechanisms.
Maybe the following article will help clear things up.

http://www.yoda.arachsys.com/csharp/parameters.html

Brian

Mi************@ gmail.com wrote:

nevermind...

I tried it without the ref and it worked, so I just answered my own
question.... for some reason i thought it wouldn't.

I guess the ref is assumed when you are dealing with eventhandlers.

[Nicholas Paldino [.NET/C# MVP]]

On a side note, for your class, I would not use an Allowed property.
Rather, I would derive the EventArgs class from CancelEventArgs , found in
the System.Componen tModel namespace.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard. caspershouse.co m

<Mi************ @gmail.comwrote in message
news:11******** **************@ i42g2000cwa.goo glegroups.com.. .

thanks.

Brian Gideon wrote:

>Michael,

I think you may be a little confused about value and reference types
and how they behave with the different parameter passing mechanisms.
Maybe the following article will help clear things up.

http://www.yoda.arachsys.com/csharp/parameters.html

Brian

Mi************@ gmail.com wrote:

nevermind...

I tried it without the ref and it worked, so I just answered my own
question.... for some reason i thought it wouldn't.

I guess the ref is assumed when you are dealing with eventhandlers.

[Michael.Suarez]

Thanks for the note.
The reason I create my own EventArgs class with an allowed property, is
that i also have a text property to pass the user the text that needs
to be analyzed to method so that the method can determine if this text
should be allowed to be added to the listview.
Nicholas Paldino [.NET/C# MVP] wrote:

On a side note, for your class, I would not use an Allowed property.
Rather, I would derive the EventArgs class from CancelEventArgs , found in
the System.Componen tModel namespace.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard. caspershouse.co m

<Mi************ @gmail.comwrote in message
news:11******** **************@ i42g2000cwa.goo glegroups.com.. .

thanks.

Brian Gideon wrote:

Michael,

I think you may be a little confused about value and reference types
and how they behave with the different parameter passing mechanisms.
Maybe the following article will help clear things up.

http://www.yoda.arachsys.com/csharp/parameters.html

Brian

Mi************@ gmail.com wrote:
nevermind...

I tried it without the ref and it worked, so I just answered my own
question.... for some reason i thought it wouldn't.

I guess the ref is assumed when you are dealing with eventhandlers.

[Nicholas Paldino [.NET/C# MVP]]

Michael,

I understand that, but what I am saying is that instead of using the
EventArgs class as your base, use the CancelEventArgs and you won't have to
worry about the Cancel property, it's there for you in the base. Then you
can add the properties that you need in your specialization.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard. caspershouse.co m
<Mi************ @gmail.comwrote in message
news:11******** **************@ e3g2000cwe.goog legroups.com...

Thanks for the note.
The reason I create my own EventArgs class with an allowed property, is
that i also have a text property to pass the user the text that needs
to be analyzed to method so that the method can determine if this text
should be allowed to be added to the listview.
Nicholas Paldino [.NET/C# MVP] wrote:

>On a side note, for your class, I would not use an Allowed property.
Rather, I would derive the EventArgs class from CancelEventArgs , found in
the System.Componen tModel namespace.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard. caspershouse.co m

<Mi*********** *@gmail.comwrot e in message
news:11******* *************** @i42g2000cwa.go oglegroups.com. ..

thanks.

Brian Gideon wrote:
Michael,

I think you may be a little confused about value and reference types
and how they behave with the different parameter passing mechanisms.
Maybe the following article will help clear things up.

http://www.yoda.arachsys.com/csharp/parameters.html

Brian

Mi************@ gmail.com wrote:
nevermind...

I tried it without the ref and it worked, so I just answered my own
question.... for some reason i thought it wouldn't.

I guess the ref is assumed when you are dealing with eventhandlers.