Contents tagged with C#

A Quick Fix for the Validator SetFocusOnError Bug

Friday, June 29, 2007

10 Comments

The ASP.NET validators have this nice property called "SetFocusOnError" that is supposed to set the focus to the first control that failed validation. This all works great until your validator control is inside a naming container. I ran into this recently when using validators in a DetailsView. Take this simple example:

<%@ Page Language="C#" %>
<script runat="server">
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
            DataBind();
    }
</script>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
<form id="_frm" runat="server">
    <asp:DetailsView 
        ID="dv1" 
        DefaultMode="Edit" 
        DataSource='<%# new object[1] %>' 
        runat="server"
    >
    <Fields>
        <asp:TemplateField HeaderText="First Name:">
            <EditItemTemplate>
                <asp:TextBox ID="FirstNameTextBox" runat="server" />
                <asp:RequiredFieldValidator 
                    ID="FirstNameValidator1"
                    ControlToValidate="FirstNameTextBox"
                    ErrorMessage="First name is required."
                    Display="Dynamic"
                    EnableClientScript="false"
                    SetFocusOnError="true"
                    ValidationGroup="bug"
                    Text="*"
                    runat="server" 
                />
            </EditItemTemplate>
        </asp:TemplateField>
    </Fields>
    <FooterTemplate>
        <asp:ValidationSummary 
            ID="vs1"
            DisplayMode="List"
            ValidationGroup="bug"
            runat="server" 
        />
        <asp:Button 
            ID="Button1" 
            Text="Post Back"
            ValidationGroup="bug" 
            runat="server" 
        />
    </FooterTemplate>
    </asp:DetailsView>
</form>
</body>
</html>

If you run this page and do a view source you'll see that the FirstNameTextBox gets rendered like this:

<input name="dv1$FirstNameTextBox" type="text" id="dv1_FirstNameTextBox" />

If you just do a post back without entering a value to cause the validator to fail it will output this line of java script in an attempt to set the focus to the invalid element:

WebForm_AutoFocus('FirstNameTextBox');

See anything wrong with this? It would seem that the validators just use the string value you typed in for the ControlToValidate property rather than doing a FindControl and using the UniqueID. This is exactly what happens and I verified it with reflector. The Validate method on BaseValidator does this:

if ((!this.IsValid && (this.Page != null)) && this.SetFocusOnError)
{
  this.Page.SetValidatorInvalidControlFocus(this.ControlToValidate);
}

If you follow the call to SetValidatorInvalidControlFocus you'll see that it never resolves the full UniqueID of the control that its going to set focus to.

Ok, so this sucks. How do I work around it. My solution was to simply ditch using the SetFocusOnError property and implement the focus logic myself which is actually pretty easy. I overrode Validate method on my Page like this:

public override void Validate(string group)
{
    base.Validate(group);

    // find the first validator that failed
    foreach (IValidator validator in GetValidators(group))
    {
        if (validator is BaseValidator && !validator.IsValid)
        {
            BaseValidator bv = (BaseValidator)validator;
            
            // look up the control that failed validation
            Control target = 
                bv.NamingContainer.FindControl(bv.ControlToValidate);
            
            // set the focus to it
            if (target != null)
                target.Focus();
            
            break;
        }
    }
}

If your using C# 3 this is even easier using LINQ:

public override void Validate(string group)
{
    base.Validate(group);

    // get the first validator that failed
    var validator = GetValidators(group)
        .OfType<BaseValidator>()
        .FirstOrDefault(v => !v.IsValid);

    // set the focus to the control
    // that the validator targets
    if (validator != null)
    {
        Control target = validator
            .NamingContainer
            .FindControl(validator.ControlToValidate);

        if (target != null)
            target.Focus();
    }
}

I hope this saves someone the headache of tracking this down.

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