• December 29, 2006
• 2 min read

Validator Application Block and ASP.NET

The Validation Application Block (VAB) of the upcoming Enterprise Library v3, uses attributes to describe validations. This gives us for example the opportunity to generate ASP.NET validators based on the attributes decorated on the properties.

Take for example the NotNullValidator of VAB, this can be translated to a RequiredFieldValidator, whereas the RegexValidator can be translated to RegularExpressionValidator. You can go further with the NotNullValidator and mark required fields with a different backcolor and adding an asterix (*) to the end of the control.

I am big fan of the DetailsView control, you can simply bind a DataSource control to it, and it will automatically provide you with a caption to each control and two-way binding. Below you find an example how you can extend the BoundField control, that investigates the NotNullValidator attribute of VAB. Note that I am currently extending it for the other set of validators and in a more OO way. More info will follow later.

public class BoundFieldEx : System.Web.UI.WebControls.BoundField
{
    public override void InitializeCell(
        DataControlFieldCell cell, DataControlCellType cellType,
        DataControlRowState rowState, int rowIndex)
    {
        base.InitializeCell(cell, cellType, rowState, rowIndex);

        if ((((rowState & DataControlRowState.Edit) != DataControlRowState.Normal) && !this.ReadOnly) ||
             ((rowState & DataControlRowState.Insert) != DataControlRowState.Normal))
        {
            TextBox textBox = null;

            if (cell != null && cell.Controls.Count > 0)
                textBox = cell.Controls[0] as TextBox;

            if (textBox != null)
            {
                Type dataItemType = null;

                if (DataBinder.GetDataItem(base.Control) != null)
                    dataItemType = DataBinder.GetDataItem(base.Control).GetType();

                if (dataItemType != null)
                {
                    ValidatorAttribute attribute = IsRequired(dataItemType, base.DataField);

                    if (attribute != null)
                    {
                        string textBoxID = this.DataField;
                        textBox.ID = textBoxID;

                        RequiredFieldValidator validator = new RequiredFieldValidator();
                        validator.ControlToValidate = textBoxID;
                        validator.ID = string.Concat("RequiredValidatorOf", textBoxID);
                        validator.Display = ValidatorDisplay.Dynamic;
                        validator.ErrorMessage = attribute.MessageTemplate;
                        cell.Controls.Add(validator);
                    }
                }
            }
        }
    }

    private ValidatorAttribute IsRequired(Type dataType, string property)
    {
        PropertyInfo propertyInfo = dataType.GetProperty(property);

        if (propertyInfo != null)
        {
            foreach (Attribute attribute in propertyInfo.GetCustomAttributes(true))
            {
                if (attribute is NotNullValidatorAttribute)
                    return attribute as ValidatorAttribute;
            }
        }

        return null;
    }
}

Now you create a custom business object, called Customer, and bind it to the DetailsView through an ObjectDataSource.

public class Customer
{
    private string _firstName;
    private string _lastName;

    [NotNullValidator(MessageTemplate="Firstname cannot be empty")]
    public string FirstName
    {
        get { return _firstName; }
        set { _firstName = value; }
    }

    [NotNullValidator(MessageTemplate="Lastname cannot be empty")]
    public string LastName
    {
        get { return _lastName; }
        set { _lastName = value; }
    }

    public Customer Fill()
    {
        Customer customer = new Customer();
        customer.FirstName = "Christoph";
        customer.LastName = "De Baene";
        return customer;
    }
}

Inside your aspx page you have something like

<asp:ObjectDataSource id="customerDataSource" TypeName="IStaySharp.Business.Customer, IStaySharp.Business" DataObjectTypeName="IStaySharp.Business.Customer, IStaySharp.Business" SelectMethod="Fill" runat="server">
</asp:ObjectDataSource>

<asp:ValidationSummary runat="server"/>

<asp:DetailsView DataSourceID="customerDataSource" DefaultMode="Edit" AutoGenerateRows="false" runat="server">
    <Fields>
        <rfx:BoundField HeaderText="Firstname"  DataField="FirstName"/>
        <rfx:BoundField HeaderText="Lastname"   DataField="LastName"/>
    </Fields>
</asp:DetailsView>

Here is the result if you leave the properties empty: