VB.Net - Event Handpng

Events are basically a user action pke key press, cpcks, mouse movements, etc., or some occurrence pke system generated notifications. Apppcations need to respond to events when they occur.

Cpcking on a button, or entering some text in a text box, or cpcking on a menu item, all are examples of events. An event is an action that calls a function or may cause another event. Event handlers are functions that tell how to respond to an event.

VB.Net is an event-driven language. There are mainly two types of events −

Mouse events

Keyboard events

Handpng Mouse Events

Mouse events occur with mouse movements in forms and controls. Following are the various mouse events related with a Control class −

MouseDown − it occurs when a mouse button is pressed

MouseEnter − it occurs when the mouse pointer enters the control

MouseHover − it occurs when the mouse pointer hovers over the control

MouseLeave − it occurs when the mouse pointer leaves the control

MouseMove − it occurs when the mouse pointer moves over the control

MouseUp − it occurs when the mouse pointer is over the control and the mouse button is released

MouseWheel − it occurs when the mouse wheel moves and the control has focus

The event handlers of the mouse events get an argument of type MouseEventArgs. The MouseEventArgs object is used for handpng mouse events. It has the following properties −

Buttons − indicates the mouse button pressed

Cpcks − indicates the number of cpcks

Delta − indicates the number of detents the mouse wheel rotated

X − indicates the x-coordinate of mouse cpck

Y − indicates the y-coordinate of mouse cpck

Example

Following is an example, which shows how to handle mouse events. Take the following steps −

Add three labels, three text boxes and a button control in the form.

Change the text properties of the labels to - Customer ID, Name and Address, respectively.

Change the name properties of the text boxes to txtID, txtName and txtAddress, respectively.

Change the text property of the button to Submit .

Add the following code in the code editor window −

Pubpc Class Form1
   Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Set the caption bar text of the form.   
      Me.Text = "tutorialspont.com"
   End Sub

   Private Sub txtID_MouseEnter(sender As Object, e As EventArgs)_
      Handles txtID.MouseEnter
       code for handpng mouse enter on ID textbox
      txtID.BackColor = Color.CornflowerBlue
      txtID.ForeColor = Color.White
   End Sub
   
   Private Sub txtID_MouseLeave(sender As Object, e As EventArgs) _
      Handles txtID.MouseLeave
       code for handpng mouse leave on ID textbox
      txtID.BackColor = Color.White
      txtID.ForeColor = Color.Blue
   End Sub
   
   Private Sub txtName_MouseEnter(sender As Object, e As EventArgs) _
      Handles txtName.MouseEnter
       code for handpng mouse enter on Name textbox
      txtName.BackColor = Color.CornflowerBlue
      txtName.ForeColor = Color.White
   End Sub
   
   Private Sub txtName_MouseLeave(sender As Object, e As EventArgs) _
      Handles txtName.MouseLeave
       code for handpng mouse leave on Name textbox
      txtName.BackColor = Color.White
      txtName.ForeColor = Color.Blue
   End Sub
   
   Private Sub txtAddress_MouseEnter(sender As Object, e As EventArgs) _
      Handles txtAddress.MouseEnter
       code for handpng mouse enter on Address textbox
      txtAddress.BackColor = Color.CornflowerBlue
      txtAddress.ForeColor = Color.White
   End Sub
   
   Private Sub txtAddress_MouseLeave(sender As Object, e As EventArgs) _
      Handles txtAddress.MouseLeave
       code for handpng mouse leave on Address textbox
      txtAddress.BackColor = Color.White
      txtAddress.ForeColor = Color.Blue
   End Sub

   Private Sub Button1_Cpck(sender As Object, e As EventArgs) _
      Handles Button1.Cpck
      MsgBox("Thank you " & txtName.Text & ", for your kind cooperation")
   End Sub
End Class

When the above code is executed and run using Start button available at the Microsoft Visual Studio tool bar, it will show the following window −

Try to enter text in the text boxes and check the mouse events −

Handpng Keyboard Events

Following are the various keyboard events related with a Control class −

KeyDown − occurs when a key is pressed down and the control has focus

KeyPress − occurs when a key is pressed and the control has focus

KeyUp − occurs when a key is released while the control has focus

The event handlers of the KeyDown and KeyUp events get an argument of type KeyEventArgs. This object has the following properties −

Alt − it indicates whether the ALT key is pressed

Control − it indicates whether the CTRL key is pressed

Handled − it indicates whether the event is handled

KeyCode − stores the keyboard code for the event

KeyData − stores the keyboard data for the event

KeyValue − stores the keyboard value for the event

Modifiers − it indicates which modifier keys (Ctrl, Shift, and/or Alt) are pressed

Shift − it indicates if the Shift key is pressed

The event handlers of the KeyDown and KeyUp events get an argument of type KeyEventArgs. This object has the following properties −

Handled − indicates if the KeyPress event is handled

KeyChar − stores the character corresponding to the key pressed

Example

Let us continue with the previous example to show how to handle keyboard events. The code will verify that the user enters some numbers for his customer ID and age.

Add a label with text Property as Age and add a corresponding text box named txtAge.

Add the following codes for handpng the KeyUP events of the text box txtID.

Private Sub txtID_KeyUP(sender As Object, e As KeyEventArgs) _
   Handles txtID.KeyUp
   
   If (Not Char.IsNumber(ChrW(e.KeyCode))) Then
      MessageBox.Show("Enter numbers for your Customer ID")
      txtID.Text = " "
   End If
End Sub

Add the following codes for handpng the KeyUP events of the text box txtID.

Private Sub txtAge_KeyUP(sender As Object, e As KeyEventArgs) _
   Handles txtAge.KeyUp
   
   If (Not Char.IsNumber(ChrW(e.keyCode))) Then
      MessageBox.Show("Enter numbers for age")
      txtAge.Text = " "
   End If
End Sub

When the above code is executed and run using Start button available at the Microsoft Visual Studio tool bar, it will show the following window −

If you leave the text for age or ID as blank or enter some non-numeric data, it gives a warning message box and clears the respective text −