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Event statement

Table of contents
  1. Syntax
  2. Remarks
  3. Example

Declares a user-defined event.


[ Public ] Event procedurename [ (arglist) ]

The Event statement has these parts:

Part Description
Public Optional. Specifies that the Event is visible throughout the project. Events types are Public by default. Note that events can only be raised in the module in which they are declared.
procedurename Required. Name of the event; follows standard variable naming conventions.

The arglist argument has the following syntax and parts:

[ ByVal | ByRef ] varname [ ( ) ] [ As type ]

Part Description
ByVal Optional. Indicates that the argument is passed by value.
ByRef Optional. Indicates that the argument is passed by reference. ByRef is the default in Visual Basic.
varname Required. Name of the variable representing the argument being passed to the procedure; follows standard variable naming conventions.
type Optional. Data type of the argument passed to the procedure; may be Byte, Boolean, Integer, Long, Currency, Single, Double, Decimal (not currently supported), Date, String (variable length only), Object, Variant, a user-defined type, or an object type.


After the event has been declared, use the RaiseEvent statement to fire the event. A syntax error occurs if an Event declaration appears in a standard module. An event can't be declared to return a value. A typical event might be declared and raised as shown in the following fragments.

' Declare an event at module level of a class module
Event LogonCompleted(UserName As String)
    RaiseEvent LogonCompleted("AntoineJan")
End Sub


The following example uses events to count off seconds during a demonstration of the fastest 100-meter race. The code illustrates all of the event-related methods, properties, and statements, including the Event statement.

The class that raises an event is the event source, and the classes that implement the event are the sinks. An event source can have multiple sinks for the events it generates. When the class raises the event, that event is fired on every class that has elected to sink events for that instance of the object.

The example also uses a form (Form1) with a button (Command1), a label (Label1), and two text boxes (Text1 and Text2). When you click the button, the first text box displays "From Now" and the second starts to count seconds. When the full time (9.84 seconds) has elapsed, the first text box displays "Until Now" and the second displays "9.84".

The code specifies the initial and terminal states of the form. It also contains the code executed when events are raised.

Option Explicit

Private WithEvents mText As TimerState

Private Sub Command1_Click()
    Text1.Text = "From Now"
    Text2.Text = "0"
    Call mText.TimerTask(9.84)
End Sub

Private Sub Form_Load()
    Command1.Caption = "Click to Start Timer"
    Text1.Text = ""
    Text2.Text = ""
    Label1.Caption = "The fastest 100 meter run took this long:"
    Set mText = New TimerState
End Sub

Private Sub mText_ChangeText()
    Text1.Text = "Until Now"
    Text2.Text = "9.84"
End Sub

Private Sub mText_UpdateTime(ByVal dblJump As Double)
    Text2.Text = str(Format(dblJump, "0"))
End Sub

The remaining code is in a class module named TimerState. The Event statements declare the procedures initiated when events are raised.

Option Explicit
Public Event UpdateTime(ByVal dblJump As Double)
Public Event ChangeText()
Public Sub TimerTask(ByVal Duration As Double)
    Dim dblStart As Double
    Dim dblSecond As Double
    Dim dblSoFar As Double
    dblStart = Timer
    dblSoFar = dblStart
    Do While Timer < dblStart + Duration If Timer - dblSoFar >= 1 Then
            dblSoFar = dblSoFar + 1
            RaiseEvent UpdateTime(Timer - dblStart)
        End If
    RaiseEvent ChangeText
End Sub

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