Extended Error Provider

• Download source link (VB) - 36.03 KB (Visual Studio 2003)
• Download source link (C#) - 34.08 KB (Visual Studio 2005)

Introduction

This article explains how a basic Error Provider class can be extended to include more functionality. This extended class can reduce coding significantly for validating mandatory objects on Windows Form.

Features

1. Validate multiple controls without writing events for each control separately.

   If you use basic Error Provider, you need to write validating event for each control that you want to check. For example, for checking txtStudentName text box control, you might write code as below:

   Private Sub txtStudentName_Validating(ByVal sender As Object, _
   	ByVal e As System.ComponentModel.CancelEventArgs) _
   	Handles txtStudentName.Validating
       If txtStudentName.Text = "" Then
           ErrorProvider1.SetError(txtStudentName, "Please enter student name")
       Else
           ErrorProvider1.SetError(txtStudentName, "")
       End If
   End Sub

   You need to write the same event for each control that you want to validate. It increases code significantly in bigger projects.

   But with extended error provider, all you need to write is just:

   MyErrorProvider.Controls.Add(txtStudentName, "Student Full Name", _
   	"Please enter student name")

2. Display custom message box.

   With extended error provider, you can set custom error message box for missing fields which are mandatory.

3. Conditional validation of controls.

   You can enable or disable validation control based upon certain conditions.

Usage of ErrorProviderExtended class

1. Method for adding controls:

   MyErrorProvider.Controls.Add(<ControlName> as String,<DisplayName(Optional)>
   as String,<ErrorMessage(Optional)> as String)

2. Setting summary message:

     MyErrorProvider.SummaryMessage = "Following fields are mandatory,"

3. Enabling/Disabling control validation:

     MyErrorProvider.Controls(txtEmergencyContact).Validate = False

Using the Code

Open ErrorProvidelExtended.sln in Visual Studio .NET. There are two projects inside ErrorProvidelExtended.sln. The first project is Extended Error Provider class. The second project is a sample usage for extended error provider.

Using the extended error provider is fairly simple. The description of code is included as comments.

'Declare a variable
Dim MyErrorProvider As New ErrorProviderExtended

    Private Sub TestForm_Load(ByVal sender As System.Object, _
	ByVal e As System.EventArgs) Handles MyBase.Load
        'Add controls one by one in error provider.
        MyErrorProvider.Controls.Add(txtStudentName, "Student Full Name")
        MyErrorProvider.Controls.Add(txtStudentAge, "Age")
        MyErrorProvider.Controls.Add(txtEmergencyContact, "Emergency Contact Number")
        'Initially make emergency contact field as non mandatory
        MyErrorProvider.Controls(txtEmergencyContact).Validate = False
        'Set summary error message
        MyErrorProvider.SummaryMessage = "Following fields are mandatory,"
    End Sub

    Private Sub cmdSubmit_Click(ByVal sender As System.Object, _
	ByVal e As System.EventArgs) Handles cmdSubmit.Click
        'Following function checks all empty fields and returns TRUE 
        'if all fields are entered.
        'If any mandatory field is empty this function displays a message 
        'and returns FALSE.
        If MyErrorProvider.CheckAndShowSummaryErrorMessage = True Then
            MessageBox.Show("Data submitted successfully.")
        End If
    End Sub

    Private Sub chkAge_CheckedChanged(ByVal sender As System.Object, _
	ByVal e As System.EventArgs) Handles chkAge.CheckedChanged
        If chkAge.Checked Then
            'if student's age is less than 10, emergency contact is mandatory
            MyErrorProvider.Controls(txtEmergencyContact).Validate = True
        Else
            'if student's age is greater than 10, emergency contact is not mandatory
            MyErrorProvider.Controls(txtEmergencyContact).Validate = False
        End If
    End Sub
End Class

Description of ErrorProviderExtended class is included as comments in the source code.

Points of Interest

I have used an extended collection base class for ErrorProviderExtended.Controls property. It uses the ValidationControlCollection class which is derived from the CollectionBase class. Each control is of type ValidationControl. ValidationControl class has all required properties like DisplayName, ErrorMessage, Validate, ControlObj, etc.

Updates

The source code is now available in C# (Visual Studio 2005) edition.