.NET MAUI DataForm Error Message Styling

The DatePicker control for .NET MAUI provides styling options for customizing the appearance of the error message that appears when the entered data is invalid.

The style of the error message can be set individually for each editor or directly to the DataForm control using the following styling properties:

• ErrorImageSource(ImageSource)—Specifies the ImageSource of the image displayed in the error message.
• ErrorImageStyle(of type Style with target type Image)—Defines the error image style.
• ErrorLabelStyle(of type Style with target type Label)—Defines the error label style.

1. Defining two different ErrorLabelStyle:

• XAML
• XAML

<Style x:Key="ErrorLabelStyle" TargetType="Label">
    <Setter Property="TextColor" Value="Orange" />
    <Setter Property="VerticalTextAlignment" Value="Center" />
    <Setter Property="HorizontalTextAlignment" Value="Center" />
</Style>

<Style x:Key="ErrorLabelStyleAlt" TargetType="Label">
    <Setter Property="TextColor" Value="DarkGray" />
    <Setter Property="VerticalTextAlignment" Value="Center" />
    <Setter Property="HorizontalTextAlignment" Value="Center" />
</Style>

2. Apply common ErrorLabelStyle for all editors:

• XAML

<telerik:RadDataForm x:Name="dataFormCommonErrorStyle" 
                     Grid.Row="1" 
                     ErrorLabelStyle="{StaticResource ErrorLabelStyle}"
                     ValidationMode="LostFocus">
    <telerik:RadDataForm.BindingContext>
        <local:DataTypeEditorsModel />
    </telerik:RadDataForm.BindingContext>
</telerik:RadDataForm>

Note that local in the snippet above points to the namespace where the DataTypeEditorsModel is defined.

3. Apply ErrorLabelStyle per editor:

• XAML

<telerik:RadDataForm x:Name="dataFormIndividualErrorStyle" 
                     AutoGenerateItems="False" 
                     Grid.Row="3"  
                     ValidationMode="LostFocus">
    <telerik:DataFormRadEntryEditor PropertyName="FirstName" 
                                HeaderText="Name" 
                                ErrorLabelStyle="{StaticResource ErrorLabelStyle}" />
    <telerik:DataFormRadNumericEditor PropertyName="Email" 
                                      HeaderText="Email address" 
                                      Minimum="1" 
                                      ErrorLabelStyle="{StaticResource ErrorLabelStyleAlt}" />
    <telerik:RadDataForm.BindingContext>
        <local:DataTypeEditorsModel />
    </telerik:RadDataForm.BindingContext>
</telerik:RadDataForm>

Note that local in the snippet above points to the namespace where the DataTypeEditorsModel is defined.

4. Add the following namespace:

• XAML

xmlns:telerik="http://schemas.telerik.com/2022/xaml/maui"

5. The ViewModel used for the DataForm editors

• C#

public class DataTypeEditorsModel : NotifyPropertyChangedBase
{
    private string name;
    private DateOnly? startDate;
    private TimeOnly? startTime;
    private DateTime? endDateTime;
    private double? people = 1;
    private bool visited;
    private string phoneNumber;
    private string email;
    private string password;
    private string? url;
    private decimal? cost;
    private string? notes;
    private TimeSpan? duration;
    private EnumValue accommodation = EnumValue.Apartment;
    public enum EnumValue
    {
        SingleRoom,
        Apartment,
        House
    }

    [Required]
    [Display(Name = "First Name")]
    [DataType(DataType.Text)]
    public string FirstName
    {
        get => this.name;
        set => this.UpdateValue(ref this.name, value);
    }

    [Required]
    [Display(Name = "Email address")]
    [DataType(DataType.EmailAddress)]
    [RegularExpression("^([\\w\\.\\-]+)@([\\w\\-]+)((\\.(\\w){2,3})+)$", ErrorMessage = "Please enter valid email address.")]
    public string Email
    {
        get => this.email;
        set => this.UpdateValue(ref this.email, value);
    }

    [Required]
    [Display(Name = "Phone number")]
    [DataType(DataType.PhoneNumber)]
    [RegularExpression("^(?!0+$)(\\+\\d{1,3}[- ]?)?(?!0+$)\\d{10,15}$", ErrorMessage = "Please enter valid phone number.")]
    public string PhoneNumber
    {
        get => this.phoneNumber;
        set => this.UpdateValue(ref this.phoneNumber, value);
    }

    [Required]
    [Display(Name = "Enter password")]
    [RegularExpression("^(?=.*?[A-Z])(?=.*?[a-z])(?=.*?[0-9])(?=.*?[#?!@$%^&*-]).{8,}", ErrorMessage = "Password must contain: -at least one upper case, " +
        "at least one lower case, at least one digit, at least one special character and to be at least 8 symbols")]
    [DataType(DataType.Password)]
    public string Password
    {
        get => this.password;
        set => this.UpdateValue(ref this.password, value);
    }

    [Required]
    [Display(Name = "Star date")]
    [DataType(DataType.Date)]
    public DateOnly? StartDate
    {
        get => this.startDate;
        set => this.UpdateValue(ref this.startDate, value);
    }

    [Required]
    [Display(Name = "Start time")]
    [DataType(DataType.Time)]
    public TimeOnly? StartTime
    {
        get => this.startTime;
        set => this.UpdateValue(ref this.startTime, value);
    }

    [Required]
    [Display(Name = "End date and time")]
    [DataType(DataType.DateTime)]
    public DateTime? EndDateTime
    {
        get => this.endDateTime;
        set => this.UpdateValue(ref this.endDateTime, value);
    }

    [Display(Name = "Number of People")]
    public double? People
    {
        get => this.people;
        set => this.UpdateValue(ref this.people, value);
    }

    [Display(Name = "Select accomodation")]
    public EnumValue Accommodation
    {
        get
        {
            return this.accommodation;
        }
        set
        {
            if (this.accommodation != value)
            {
                this.accommodation = value;
                this.OnPropertyChanged();
            }
        }
    }

    [Display(Name = "Visited before")]
    public bool Visited
    {
        get => this.visited;
        set => this.UpdateValue(ref this.visited, value);
    }

    [Display(Name = "Duration")]
    public TimeSpan? Duration
    {
        get => this.duration;
        set => this.UpdateValue(ref this.duration, value);
    }

    [Display(Name = "Web address")]
    [DataType(DataType.Url)]
    [RegularExpression("^(http:\\/\\/www\\.|https:\\/\\/www\\.|http:\\/\\/|https:\\/\\/)?[a-z0-9]+([\\-\\.]{1}[a-z0-9]+)*\\.[a-z]{2,5}(:[0-9]{1,5})?(\\/.*)?$", ErrorMessage = "Please enter valid url.")]
    public string? URL
    {
        get => this.url;
        set => this.UpdateValue(ref this.url, value);
    }

    [Display(Name = "Total cost")]
    [DataType(DataType.Currency)]
    [DisplayFormat(DataFormatString = "C")]
    public decimal? Cost
    {
        get => this.cost;
        set => this.UpdateValue(ref this.cost, value);
    }

    [Display(Name = "Notes")]
    [DataType(DataType.MultilineText)]
    public string? Notes
    {
        get => this.notes;
        set => this.UpdateValue(ref this.notes, value);
    }
}

The following image shows what the DataForm control looks like when the styles described above are applied:

For a runnable example with the DataForm Error Message Styling scenario, see the SDKBrowser Demo Application and go to DataForm > Styling category.