Question

In MVVM IDataErrorInfo is used for validation. In this on which time indexer check value can not get. and after calling it how it check value i can not get.the code is here. what is the value passed in column name.

public string this[string columnName]
{
    get { return GetValidationError(columnName); }
}

why use indexer for validation in wpf .can any one say about it.

Answer 1

If you use the IDataErrorInfo interface, you validate the class that implements the interface.

If you have a property Name, activate the validation and change the property, the indexer is called with string columnName = “Name”. Now you can handle the “Name” validation in an if statement

if(columnName  == "Name")
    // do Name validation

//edit

the validation is fired in wpf if you change the property by binding. You should decorate your binding like this:

Text="{Binding UpdateSourceTrigger=LostFocus, Path=FirstName, ValidatesOnDataErrors=true, NotifyOnValidationError=true}"

Here is a nice and simple explanation of the IDataErrorInfo implementation using WPF databinding and an errortemplate.

WPF: Validation made easy with IDataErrorInfo