WPF Complex Validation

Question

Ok, so I have a WPF Application (using MVVM) consisting of a View that has two textboxes: First Name and Last Name.

Both of them must consist of only letters. I've achieved that by using attributes on the corresponding entity (Worker):

[RegularExpression(@"^[a-zA-Z]+$", ErrorMessage = "First Name must consist of letters only.")]


public string FirstName



[RegularExpression(@"^[a-zA-Z]+$", ErrorMessage = "Last Name must consist of letters only.")]


public string LastName

And it works great. But...I also need to have the following validation rule: At least one of the fields: FirstName or LastName Must be filled.

Any ideas on how to implement validation involving two fields?

The expected result is: If non of the fields is filled, then a validation msg will appear beside the FirstName textbox: At least first name or last name must be filled. The same message will also appear near the the last name textbox. Once I fill one of those fields, Both messages will disppear.

Another challenge, is that if I enter a digit in first name textbox, I want an error message only on the First name textbox: First Name must consist of letters only. And I want the error of at least one of the fields must be filled (near both of the textboxes) to dissapear.

Thanks!

Read this great article on WPF validation as well. msdn.microsoft.com/en-us/magazine/ff714593.aspx — ChrisO

Sheridan Sheridan · Accepted Answer · 2014-06-27T14:47:45

You'd be better off implementing the IDataErrorInfo Interface, or if you're using .NET 4.5, the newer INotifyDataErrorInfo Interface. Using the IDataErrorInfo interface as an example, you'd need to implement an indexer for your data type class and in the indexer, you can define any complicated rules that you can think of:

public override string this[string propertyName]
{
    get
    {
        string error = string.Empty;
        if ((propertyName == "FirstName" || propertyName == "LastName") && 
            (FirstName == string.Empty || LastName == string.Empty)) 
            error = "You must enter either the First Name or Last Name fields.";
        return error;
    }
}

WPF Complex Validation

2 Answers