Languages

This page is also available in 简体中文 and 日本語.

[BindableValidator] and validation

BindableValidator is an abstract base class that implements both INotifyPropertyChanged and INotifyDataErrorInfo, backed by System.ComponentModel.DataAnnotations. The generator can wire it up automatically in two ways.

Option A — inherit BindableValidator directly

Inherit BindableValidator and mark properties with [ObservableProperty] + [NotifyDataErrorInfo]. The generator emits ValidateProperty(value, nameof(Property)) in each setter.

public partial class LoginViewModel : BindableValidator
{
    [ObservableProperty]
    [NotifyDataErrorInfo]
    [Required(ErrorMessage = "Username is required.")]
    [MinLength(2, ErrorMessage = "At least 2 characters.")]
    public partial string Username { get; set; } = "";

    [ObservableProperty]
    [NotifyDataErrorInfo]
    [Required(ErrorMessage = "Email is required.")]
    [EmailAddress(ErrorMessage = "Enter a valid email address.")]
    public partial string Email { get; set; } = "";
}

Option B — use [BindableValidator] attribute

For classes that already have a base class (or simply want the generator to wire everything up), annotate the partial class with [BindableValidator]:

• If the type has no declared base (only object), the generated partial inherits BindableValidator.
• If the type already has a base, the generator emits INotifyDataErrorInfo and validation helpers directly into the partial, reusing any existing INotifyPropertyChanged from the hierarchy.

The type must be partial (PSG0005). Non-class types (structs, interfaces) produce PSG0006.

[BindableValidator]
public partial class ProfileViewModel
{
    [ObservableProperty]
    [NotifyDataErrorInfo]
    [Required(ErrorMessage = "Display name is required.")]
    [MaxLength(20, ErrorMessage = "20 characters max.")]
    public partial string DisplayName { get; set; } = "";

    [ObservableProperty]
    [NotifyDataErrorInfo]
    [Range(1, 120, ErrorMessage = "Age must be between 1 and 120.")]
    public partial int Age { get; set; }
}

When the class has no explicit base type, the generator makes the partial inherit BindableValidator:

// Generated (simplified)
public partial class ProfileViewModel : Prism.SourceGenerators.BindableValidator { }

All ValidateProperty calls, HasErrors, and other members come from BindableValidator automatically.

Class-level [NotifyDataErrorInfo]

Apply [NotifyDataErrorInfo] to the class to enable validation on all generated properties in one go:

[NotifyDataErrorInfo]
public partial class RegisterViewModel : BindableValidator
{
    [ObservableProperty]
    [Required]
    public partial string Username { get; set; } = "";

    [ObservableProperty]
    [EmailAddress]
    public partial string Email { get; set; } = "";
}

Available methods

BindableValidator exposes:

Method	Description
ValidateProperty(value, name)	Validate a single property; updates ErrorsChanged.
ValidateAllProperties()	Run validation on every property at once.
ClearErrors(name)	Clear errors for a specific property.
ClearAllErrors()	Clear all validation errors.
GetErrors(name)	Return current errors (IEnumerable).
HasErrors	true when any property has errors.

DataAnnotations forwarding

[Required], [EmailAddress], [MinLength] and other ValidationAttribute-derived attributes placed on a partial property declaration stay on the user's declaration only — the generator does not re-emit them on the implementing partial, avoiding CS0579 while keeping Validator metadata correct.

For field targets, untargeted DataAnnotations attributes are forwarded to the generated property so the validator can see them.

Diagnostic

ID	Severity	Condition
PSG5001	Warning	[NotifyDataErrorInfo] used but the type does not inherit BindableValidator or use [BindableValidator] — validation calls will not be emitted.

Related

• ObservableProperty
• Notifications & forwarding
• Diagnostics reference