How to use IDataErrorInfo.Error in a WPF program? - wpf

Question

I have an object like that:
public class Person : IDataErrorInfo
{
public string PersonName{get;set;}
public int Age{get;set;}
string IDataErrorInfo.this[string propertyName]
{
get
{
if(propertyName=="PersonName")
{
if(PersonName.Length>30 || PersonName.Length<1)
{
return "Name is required and less than 30 characters.";
}
}
return null;
}
}
string IDataErrorInfo.Error
{
get
{
if(PersonName=="Tom" && Age!=30)
{
return "Tom must be 30.";
}
return null;
}
}
}
Binding the PersonName and Age properties is easy:
<TextBox Text="{Binding PersonName, ValidatesOnDataErrors=True}" />
<TextBox Text="{Binding Age, ValidatesOnDataErrors=True}" />
However, how can I use the Error property and show it appropriately?

Answer 1

You should modify the TextBox style so it shows what's wrong with the property. Here is a simple example that shows the error as tooltip:
<Style TargetType="TextBox">
<Style.Triggers>
<Trigger Property="Validation.HasError" Value="true">
<Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self},
Path=(Validation.Errors).CurrentItem.ErrorContent}" />
</Trigger>
</Style.Triggers>
</Style>
Just put it inside Application.Resources from your app.xaml file and it will be aplied for every textbox of your application:
<Application.Resources>
<Style TargetType="TextBox">
<Style.Triggers>
<Trigger Property="Validation.HasError" Value="true">
<Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self},
Path=(Validation.Errors).CurrentItem.ErrorContent}" />
</Trigger>
</Style.Triggers>
</Style>
</Application.Resources>

Answer 2

Here is an example, adapted from this question, that shows how to display the error in Tooltip:
<TextBox>
<TextBox.Style>
<Style TargetType="{x:Type TextBox}">
<Style.Triggers>
<Trigger Property="Validation.HasError" Value="true">
<Setter Property="ToolTip"
Value="{Binding RelativeSource={RelativeSource Self},
Path=(Validation.Errors)[0].ErrorContent}"/>
</Trigger>
</Style.Triggers>
</Style>
</TextBox.Style>
</TextBox>