INotifyDataErrorInfo. ErrorsChanged how to make wpf show the errors of property like `Address.Country`

Question

There is only 3 things inside of INotifyDataErrorInfo:

HasErrors: a read-only boolean property which tells if the object as a whole have any validation errors;
GetErrors: a method which returns validation errors for a given property;
ErrorsChanged: an event which must be raised when new errors – or the lacks of errors – is detected. You have to raise this event for each property.

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In the demo project I create a form which display the properties of an object named ‘Person’. Here is how the validation with INotifyDataErrorInfo is enabled in the Binding:

<TextBox Text="{Binding Name,Mode=TwoWay,ValidatesOnNotifyDataErrors=True}"/>

We have to set the ValidatesOnNotifyDataErrors property to true.

The binding will then register itself for the ErrorsChanged event of the binded Person. Eeach time this event is raised for the binded property, the controls will dress itself to display an error. this is done only if the HasErrors is set to true.

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Question:

1. Is there anyone know more detail aobut the ErrorsChanged event is raised for the binded property, the controls will dress itself to display an error?

2. If I binding Address.Country of Person ,will the ErrorsChanged event be raised for the binded property Address.Country or not? why? is there a way make this binding to show Errors too?

   <TextBox Text="{Binding Address.Country,Mode=TwoWay,ValidatesOnNotifyDataErrors=True}"/>

Answer 1

I think I can risk an answer, this question is already one year old.

The Binding will register to the ErrorsChanged event in the Class containing the property. In that case, Address must implement INotifyDataErrorInfo.

And, it's you to raise the ErrorsChanged event when you implement the validation logic. Once you have validated the Address.Country, you store the ValidationResults (or simple strings list) and raise the event. The Binding will get the stored ValidationResults list for the PropertyName he is binded to, by calling the method GetErrors(string propertyName)that you wrote yourself implementing the INotifyDataErrorInfo interface.

If this list is not empty, the Binding will set the Property Validation.HasError to True and the control will raise the Validation.Error event. Some controls have a built-in behavior to change their appearance in error case (a TextBox will have a red frame around its border). If you want to show the errors, you have to retrieve them by writing a style in xaml. Plenty of examples out there.

The HasErrors method is used if you want to know if the Person has any errors in its Properties. It's mostly used in such cases : enabling or disabling a save button. Once again, it's you to implement the logic using the HasErrors Property. It's mostly done by binding it to a control Property in xaml.