VB.NET Technology

This control provides a user interface that indicates to user that a control on a form has error associated with it. In other had it works as validation upon the controls to handle the error causes by inputting wrong by user.

Drag this control as shown in below picture

Adding error provider control on textbox for blank not allow

Write this code on textbox validating event

Output will shown in below picture if user leave name blank.

Private Sub TextBox1_Validating(ByVal sender As System.Object, 
	ByVal e As System.ComponentModel.CancelEventArgs) Handles TextBox1.Validating
        ValidateName()
    End Sub
    Private Function ValidateName() As Boolean
        Dim bStatus As Boolean = True
        If textBox1.Text = "" Then
            errorProvider1.SetError(textBox1, "Please enter your Name")
            bStatus = False
        Else
            errorProvider1.SetError(textBox1, "")
        End If
        Return bStatus
    End Function

Validating for age. For validating age i have covered three conditions for validate

If user leave this blank.
If entered age is less than 18.
If user input character value in place of numeric.

Write this code on Textbox2 validating Event

Private Sub TextBox2_TextChanged(ByVal sender As System.Object, 
ByVal e As System.EventArgs) Handles TextBox2.TextChanged
        ValidateAge()
    End Sub
    Private Function ValidateAge() As Boolean
        Dim bStatus As Boolean = True
        If textBox2.Text = "" Then
            errorProvider1.SetError(textBox2, "Please enter your Age")
            bStatus = False
        Else
            errorProvider1.SetError(textBox2, "")
            Try
                Dim temp As Integer = Integer.Parse(textBox2.Text)
                errorProvider1.SetError(textBox2, "")
                If temp < 18 Then
                    errorProvider1.SetError(textBox2, 
			"You must be atleast 18 years old to setup a test")
                    bStatus = False
                Else
                    errorProvider1.SetError(textBox2, "")
                End If
            Catch
                errorProvider1.SetError(textBox2, "Please enter your age as a number")
                bStatus = False
            End Try
        End If
        Return bStatus
    End Function

Output of this error provider is shown below

Using error provider control on DatetimePicker Control

If user select weekend day for test then he will get error message- Like shown in below picture

Private Sub DateTimePicker1_Validating(ByVal sender As System.Object, 
	ByVal e As System.ComponentModel.CancelEventArgs) 
	Handles DateTimePicker1.Validating
        ValidateTestDate()
    End Sub
Private Function ValidateTestDate() As Boolean
        Dim bStatus As Boolean = True
        If (dateTimePicker1.Value.DayOfWeek = DayOfWeek.Sunday) 
	OrElse (dateTimePicker1.Value.DayOfWeek = DayOfWeek.Saturday) Then
            errorProvider1.SetError(dateTimePicker1,
	 "Appointment cannot be scheduled in the weekend. Please select a weekday")
            bStatus = False
        Else
            errorProvider1.SetError(dateTimePicker1, "")
        End If
        Return bStatus
End Function