C# 0 The Complete Reference

MyButtonClick( )

 is called.

An Alternative Implementation

As a point of interest, 

MyButtonClick( )

 could have been written in a slightly different way. 

Recall that the 

who

 parameter of an event handler receives a reference to the object that 

generated the call. In the case of a button click event, this is the button that was clicked. 

Thus,

MyButtonClick( )

 could have been written like this:

// An Alternative button handler.

void MyButtonClick(object who, EventArgs e) {

  Button b = (Button) who;

  if(b.Top == 200)

    b.Location = new Point(10, 10);

  else

    b.Location = new Point(100, 200);

}

In this version, 

who

 is cast to 

Button

, and this reference (rather than the 

MyButton

field) is used to access the button object. Although there is no advantage to this approach in 

this case, it is easy to imagine situations in which it would be quite valuable. For example, 

such an approach allows a button event handler to be written independently of any specific 

button.

Using a Message Box

One of the most used built-in features of Windows is the 

message box.

 A message box is a 

predefined window that lets you display a message. You can also obtain simple responses 

from the user, such as Yes, No, or OK. In a form-based program, a message box is supported 

by the 

MessageBox

 class. You don’t create an object of that class, however. Instead, to 

display a message box, call the 

static

 method 

Show( )

, which is defined by 

MessageBox

.

The

Show( )

 method has several forms. The one we will be using is shown here:

public static DialogResult Show(string 

msg

, string 

caption

,

                                                         MessageBoxButtons 

mbb

)

The string passed through 

msg

 is displayed in the body of the box. The caption of the 

message box window is passed in 

caption.

 The buttons that will be displayed are specified 

by

mbb.

 The user’s response is returned.

MessageBoxButtons

 is an enumeration that defines the following values:

Abor tRetr yIgnore

OK

OKCancel

Retr yCancel

YesNo

YesNoCancel

Each of these values describes the buttons that will be included in a message box. For example, 

if

mbb

 contains 

YesNo

, then the Yes and No buttons are included in the message box.

The value returned by 

Show( )

 indicates which button was pressed. It will be one of 

these values, defined by the 

DialogResult

 enumeration:

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