Exception Handling in Visual Basic .NET

August 28, 2017

We will first see the following code and run the program first. Here I am going to divide two numbers and show the results in a Label.

This the code for click event handler of the Button

Public Class Form1

    Private Sub ButtonDivide_Click(sender As Object, e As EventArgs) Handles ButtonDivide.Click
        Dim number1 As Double
        Dim number2 As Double
        Dim result As Double
        
            number1 = CType(TextBoxNumber1.Text, Double)
            number2 = CType(TextBoxNumber2.Text, Double)
            result = number1 / number2
            LabelResult.Text = result

    End Sub
End Class

Leave the TextBoxes blank and You click the Button.
What will be the error you can see?
So you will get error called InvalidCastException. Because you are casting blank space to Double data type

So I will add Try… Catch statement to handle it and show error message to user

Public Class Form1

    Private Sub ButtonDivide_Click(sender As Object, e As EventArgs) Handles ButtonDivide.Click
        Dim number1 As Double
        Dim number2 As Double
        Dim result As Double
        Try
            number1 = CType(TextBoxNumber1.Text, Double)
            number2 = CType(TextBoxNumber2.Text, Double)
            result = number1 / number2
            LabelResult.Text = result


        Catch Err As InvalidCastException
            MessageBox.Show(Err.Message)
        End Try

    End Sub
End Class

Now you will get MessageBox with message Conversion from String “” to type Double is not valid

Using the Catch statement I catched the Exception and I showed custom error message to user without terminating the project