Five Minute Silverlight 4 Aides-Memoire #7 – IDataErrorInfo

The XAML:

DATA INPUT

1. <Grid x:Name="LayoutRoot">
2.   <Grid.Resources>
3.     <local:Person x:Key="NewJoiner" Age="49" Forename="Fred" Surname="Flintstone" />
4.   </Grid.Resources>
5.   <Grid DataContext="{StaticResource NewJoiner}">
6.     <Grid.ColumnDefinitions>
7.       <columndefinition Width="1*" />
8.       <columndefinition Width="5*" />
9.     </Grid.ColumnDefinitions>
10.     <Grid.RowDefinitions>
11.       <rowdefinition Height="50" />
12.       <rowdefinition Height="50" />
13.       <rowdefinition Height="50" />
14.     </Grid.RowDefinitions>
15.     <Grid.Resources>
16.       <Style TargetType="TextBlock">
17.         <setter Property="Margin" Value="10" />
18.         <setter Property="HorizontalAlignment" Value="Right" />
19.         <setter Property="VerticalAlignment" Value="Center" />
20.       </Style>
21.       <Style TargetType="TextBox">
22.         <setter Property="Margin" Value="10" />
23.         <setter Property="Width" Value="154" />
24.         <setter Property="HorizontalAlignment" Value="Left" />
25.         <setter Property="VerticalAlignment" Value="Center" />
26.       </Style>
27.     </Grid.Resources>
28.     <TextBlock Text="First Name" Grid.Row="0" Grid.Column="0" />
29.     <TextBlock Text="Last Name" Grid.Row="1" Grid.Column="0" />
30.     <TextBlock Text="Age" Grid.Row="2" Grid.Column="0" />
31.     <textbox x:Name="Forename" Grid.Row="0" Grid.Column="1" Text="{Binding Forename, Mode=TwoWay, ValidatesOnDataErrors=True}" />
32.     <textbox x:Name="Surname" Grid.Row="1" Grid.Column="1" Text="{Binding Surname, Mode=TwoWay, ValidatesOnDataErrors=True}" />
33.     <textbox x:Name="Age" Grid.Row="2" Grid.Column="1" Text="{Binding Age, Mode=TwoWay, ValidatesOnDataErrors=True}" />
34.   </Grid>
35. </Grid>

The code:

IMPLEMENTATION

1. public class Person : IDataErrorInfo
2. {
3.     public string Forename { get; set; }
4.     public string Surname { get; set; }
5.     public int Age { get; set; }
6.     public string Error { get { return null; } }
7.  
8.     public string this[string columnName]
9.     {
10.         get
11.         {
12.             string error = null;
13.             switch (columnName)
14.             {
15.                 case "Forename":
16.                     if (string.IsNullOrEmpty(Forename))
17.                         error = "Forename required";
18.                     break;
19.                 case "Surname":
20.                     if (string.IsNullOrEmpty(this.Surname))
21.                         error = "Surname required";
22.                     break;
23.                 case "Age":
24.                     if (this.Age < 0 || this.Age > 130)
25.                         error = "Invalid Age";
26.                     break;
27.             }
28.             return error;
29.         }
30.     }
31. }

The result: