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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 −
![Event Handpng Example1](/vb.net/images/vb.net_event_handpng1.jpg)
Try to enter text in the text boxes and check the mouse events −
![Event Handpng Result Form](/vb.net/images/vb.net_event_handpng2.jpg)
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 −
![VB.Net Event Example](/vb.net/images/vb.net_event_handpng3.jpg)
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 −
![VB.Net Event Example](/vb.net/images/vb.net_event_handpng4.jpg)