sender error in public class

Question

1.00/5 (1 vote)

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C#

public class aDecimal1 : TextBox
{
    protected override void OnKeyPress(KeyPressEventArgs e)
    {
        MessageBox.Show((sender as TextBox).Text);
    }
}

hi friends.
please help me
:(
error: the name 'sender' does not exist in the current context

Posted 16-May-12 5:11am

faezun

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fjdiewornncalwe · Accepted Answer · 2012-05-16T05:19:00

Solution 1

Because you are overriding the TextBox class, you don't need that part of the call. Try this:

C#

MessageBox.Show(Text);

If you place a regular TextBox on a form and then add the OnKeyPress handler on the form, the from will require a context for the call so it includes the object sender argument in the call. This is not required in your inherited aDecimal1 class as it is already instance specific. Because of this, you can just drop the sender as TextBox part.

Posted 16-May-12 5:19am

fjdiewornncalwe

Comments

faezun 16-May-12 11:21am

thanks
:)

error: the name 'text' does not exist in the current context

fjdiewornncalwe 16-May-12 13:32pm

I have tried this to confirm whether my answer is valid in both Windows.Forms and asp.net. In both cases the code works. You do have to make sure that "Text" is not written "text" as C# is case sensitive.

Sergey Alexandrovich Kryukov 18-May-12 14:32pm

"Text", not "text". It does exist.
--SA

BillW33 16-May-12 11:23am

You beat me to the answer; 5 from me :)

VJ Reddy 16-May-12 11:26am

Good answer. 5!

Sandeep Mewara 17-May-12 1:09am

5!

Sergey Alexandrovich Kryukov 18-May-12 14:33pm

My 5. I wish OP learned what "this" does and how events work; trial-and-error leads nowhere; too boring to explain it over and over...
--SA

VJ Reddy · Accepted Answer · 2012-05-16T05:24:00

The reason is that in the protected method

C#

protected override void OnKeyPress(KeyPressEventArgs e)
{
    MessageBox.Show((sender as TextBox).Text);
}

there is neither a parameter nor a local variable by name sender. Further there may not a field or property in the class with name sender. Hence, the above error.

In .NET the standard practice to implement events is to have a protected method like OnEventName. In this case the Event of TextBox is KeyPress and within the TextBox class this event is raised by calling the OnKeyPress event.

In .Net the standard pattern for events is of type

C#

public void EventName(object sender, EventArgs e) {  }

When a client subscribes to this event the client is to be informed who has raised this event so that they can use the object raising the event for some purpose.

When the protected method is used to raise the event it is already present in the concerned class and there is no need of sender. Hence, the OnEventName methods do not have sender parameter.

mr.priyank · Accepted Answer · 2012-05-16T05:22:00

Solution 2

use this instead of sender.
there is no neas to cast it.
use this.Text directly

Posted 16-May-12 5:22am

mr.priyank

Comments

faezun 16-May-12 11:39am

MessageBox.Show(Text);

error: the name 'text' does not exist in the current context

Sergey Alexandrovich Kryukov 18-May-12 14:15pm

Your approach is not going to work. You should not use trial-end-error method without understanding. Finally, you should go in depth and understand how things work. Do you understand what an event object does? And what's the role of "this", where it comes from? "This" is the one of classical OOP fundamentals, but the delegates are much more advanced. Read about all that matter, stop wasting your time and the time of others.
--SA

mr.priyank 16-May-12 12:10pm

i said MessageBox.Show(this.Text);

Sergey Alexandrovich Kryukov 18-May-12 14:11pm

Correct, a 5.
This is all what's needed.
--SA

VJ Reddy 18-May-12 20:31pm

To the point. 5!