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.NET MAUI DataForm Validation

Updated over 6 months ago

.NET MAUI DataForm provides built-in validation, which gives you full control over the data collected through the control.

The next sections list all DataForm members related to validation.

Validation Modes

The selected mode is applied through ValidationMode (of typeTelerik.Maui.Controls.DataFormValidationMode) property of the DataForm control. You can choose between three validation modes:

Explicit—The changes are validated explicitly by invoking the ValidateCommand or calling the ValidateChanges method of the DataForm.
LostFocus—The changes are validated after the editor loses focus.
PropertyChanged—The changes in the editor are validated immediately on each property change (when the property value changes).

When ValidationMode is LostFocus, you have to set CommitMode to LostFocus or Explicit.

The ValidationMode must be applied globally to the RadDataForm:

XAML

<telerik:RadDataForm x:Name="dataForm"
                     ValidationMode="LostFocus"/>

Validation Properties

HasValidationErrors(bool)—Gets a value indicating whether it has validation errors.

Events

DataForm exposes the following events for validation:

ValidationCompleted—Raised when the DataForm validation completes. The ValidationCompleted event handler receives two parameters:
- sender argument which is of type object, but can be cast to the RadDataForm type.
- DataFormObjectValidationCompletedEventArgs which provides additional information for the validated DataObject, the ValidationErros(IReadOnlyList of DataFormValidationError) and whether it has validation errors HasValidationErrors(bool).
EditorValidationCompleted—Raised when the validation of an editor has completed. The EditorValidationCompleted event handler receives two parameters:
- sender argument which is of type object, but can be cast to the RadDataForm type.
- DataFormEditorValidationCompletedEventArgs which provides additional information for the validated PropertyName, the original value ff the validated property PropertyValue(object) in the model and the modified value of the validated property in the editor - EditorValue(object).

Manual Validation with Methods

DataForm exposes a ValidateChanges method with two overloads:

ValidateChanges()—Executes the validation logic associated with the DataForm control. This method is useful when the ValidationMode is Explicit. The method returns true if the validation passes, otherwise false.

this.dataForm.ValidateChanges();

ValidateChanges(string propertyName)—Validates the pending changes in the editor for the specified property. This method is useful when the DataForm ValidationMode property is Explicit. True if the validation passes, false otherwise.

this.dataForm.ValidateChanges(propertyName);

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

Commands

ValidateCommand(ICommand)—Gets a command to execute the validation logic of the RadDataForm. This command is useful when the DataForm ValidationMode property is Explicit.

Validation Summary - Styling and Customization

The ValidationSummaryMessage displays all validation messages for the editors. You can visualize/hide the validation summary message by setting the IsValidationSummaryVisible(bool) property to True/False.

You can use the following properties for validation styling and customization:

ValidationSummaryImageSource(ImageSource)—Specifies the ImageSource of the image displayed in the validation summary.
ValidationSummaryImageStyle(Style)—Specifies the style applied to the image of the validation summary. The target type of this style is the .NET MAUI Image control.
ValidationSummaryStyle(Style)—Specifies the style applied to the validation summary. The target type of this style is the Telerik.Maui.Controls.DataFormValidationSummaryView.
ValidationSummaryLabelStyle(Style)—Specifies the style applied to the labels of the validation summary. The target type of this style is the .NET MAUI Label control.

Error Message - Styling and Customization

You can use the following properties for error message styling and customization:

ErrorImageSource(ImageSource)—Specifies the ImageSource of the image displayed in the error message.
ErrorImageStyle(Style)—Specifies the style applied to the image of the error message. The target type of this style is the .NET MAUI Image control.
ErrorLabelStyle(Style)—Specifies the style applied to the labels of the error message. The target type of this style is the .NET MAUI Label control.

Runtime Validation

If you want to add the validation runtime, when editors are generated, then you have to use the EditorsGenerated event. Inside the event you can define the validation.

The following table lists the available DataForm validations:

DataForm Validation Rule	Definition
(DataForm level) `DataFormObjectValidationRule`	Represents a custom validation rule of the DataForm control.
`DataFormEditorCustomValidationRule`	Represents a custom validation rule for the editor. The validation rule can execute a custom validation logic on the underlying business object.
`DataFormEditorLengthValidationRule`	Validates that the string length of the current value is between the specified minimum and maximum length.
`DataFormEditorRangeValidationRule`	Validates that the current value is between the specified minimum and maximum value.
`DataFormEditorRegexValidationRule`	Executes a custom regular expression to validate the current string value.
`DataFormEditorRequiredValidationRule`	Validates that the current value is not null or an empty string.

When using both runtime validation and ViewModel validation (via data annotations)—the validation defined in the ViewModel will be applied instead of the runtime validation. The Data Annotation Validation has the higher priority.

Here is an example for runtime validation using the EditorGenerated event:

var form = new RadDataForm();
form.EditorGenerated += this.OnEditorGenerated;

private void OnEditorGenerated(object sender, DataFormEditorGeneratedEventArgs eventArgs)
{
	switch (eventArgs.PropertyName)
	{
		case "FirstName":
			eventArgs.Editor.HeaderText = "First Name";
			// This won't be applied on FirstName property, as there is a validation set by using the DataAnnotations
			eventArgs.Editor.ValidationRules.Clear();
			break;
		case "LastName":
			eventArgs.Editor.HeaderText = "Last Name";
			// Add validation rule here
			eventArgs.Editor.ValidationRules.Add(new DataFormEditorRequiredValidationRule
			{

			});
			break;
		case "StartDate":
			eventArgs.Editor = new DataFormRadDatePickerEditor
			{
				PropertyName = "StartDate",
				HeaderText = "Start Date"
			};
			break;
		case "EndDate":
			// we remove the editor for this property
			eventArgs.Editor = null;
			break;
		case "Accommodation":
			eventArgs.Editor = new DataFormRadComboBoxEditor
			{
				PropertyName = "Accommodation",
				HeaderText = "Accommodation",
			};
			break;
	}
}