The following example shows how to ask the user a Yes or No question and make a decision based on the response

Private Sub ValidateUserEntry()
'Checks the value of the text.The above example also shows that we can take a response from the message box and use the value of the result to perform specific actions.

If ServerName.Text.Length = 0 Then
'Initializes variables to pass to the MessageBox.Show method.
Dim Message As String
Dim Caption As String
Dim Buttons As MessageBoxButtons
Dim Result As DialogResult

Message = "You did not enter a server name. Cancel this operation?"
Caption = "No Server Name Specified"
Buttons = MessageBoxButtons.YesNo

'Displays the MessageBox
Result = MessageBox.Show(Me, Message, Caption, Buttons)

'Gets the result of the MessageBox display.
If Result = DialogResult.Yes Then
'Closes the parent form.
Me.Close()
End If
End If
End Sub

Visual Basic has a public function MsgBox. It displays a message in a dialog box, waits for the user to click a button, and then returns an integer indicating which button the user clicked.

Public Function MsgBox( _
ByVal Prompt As Object, _
Optional ByVal Buttons As MsgBoxStyle = MsgBoxStyle.OKOnly, _
Optional ByVal Title As Object = Nothing _
) As MsgBoxResult

MessageBox class Parameters

Prompt

Required. String expression displayed as the message in the dialog box. The maximum length of Prompt is approximately 1024 characters, depending on the width of the characters used. If Prompt has more than one line, you can separate the lines using a carriage return character, a linefeed character, or a carriage return/linefeed character combination between each line.

Buttons

Optional. Numeric expression that is the sum of values specifying the number and type of buttons to display, the icon style to use, the identity of the default button, and the modality of the message box. If you omit Buttons, the default value is zero.

Title

Optional. String expression displayed in the title bar of the dialog box. If you omit Title, the application name is placed in the title bar.

Settings

The MsgBoxStyle enumeration values are listed in the following table.

The first group of values (0–5) describes the number and type of buttons displayed in the dialog box; the second group (16, 32, 48, 64) describes the icon style; the third group (0, 256, 512) determines which button is the default; the fourth group (0, 4096) determines the modality of the message box, and the fifth group specifies whether or not the message box window is the foreground window, along with the alignment and direction of the text. When adding numbers to create a final value for the Buttons argument, use only one number from each group.

First Page: Application Class and Message Class