Provide a value in "System.Windows.Data.Binding" threw an exception

Question

I add a validation rule to the text box (following examples on WPF 4 Unleashed by Adam Nathan)

When running the application, I came across the following cryptic error message

Provide value in 'System.Windows.Data.Binding' threw an exception

What does the error mean and what needs to be done to solve the problem?

Here is the complete source code

Xaml

<Window.Resources> <Style x:Key="controlStyle" TargetType="{x:Type Control}"> <Style.Triggers> <Trigger Property="IsMouseOver" Value="True"> <Setter Property="RenderTransform"> <Setter.Value> <RotateTransform Angle="20" /> </Setter.Value> </Setter> <Setter Property="Foreground" Value="Black" /> </Trigger> </Style.Triggers> <Setter Property="FontSize" Value="22" /> <Setter Property="Background" Value="Purple" /> <Setter Property="Foreground" Value="White" /> <Setter Property="Height" Value="50" /> <Setter Property="Width" Value="50" /> <Setter Property="RenderTransformOrigin" Value=".5,.5" /> <Setter Property="RenderTransform"> <Setter.Value> <RotateTransform Angle="10" /> </Setter.Value> </Setter> <Setter Property="TextBox.TextAlignment" Value="Right" /> </Style> <Style x:Key="textBoxStyle" TargetType="{x:Type TextBox}"> <Style.Triggers> <Trigger Property="Validation.HasError" Value="True"> <Setter Property="Background" Value="Red" /> <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}" /> </Trigger> </Style.Triggers> </Style> </Window.Resources> <StackPanel Orientation="Vertical"> <StackPanel Orientation="Horizontal"> <TextBox Style="{StaticResource textBoxStyle}"> <TextBox.Text> <Binding> <Binding.ValidationRules> <local:JpgValidationRule /> </Binding.ValidationRules> </Binding> </TextBox.Text> </TextBox> </StackPanel> <StackPanel Orientation="Horizontal"> <Button Style="{StaticResource controlStyle}">1</Button> <ComboBox Style="{StaticResource controlStyle}"> <ComboBox.Items>2</ComboBox.Items> </ComboBox> <Expander Style="{StaticResource controlStyle}" Content="3" /> <TabControl Style="{StaticResource controlStyle}"> <TabControl.Items>4</TabControl.Items> </TabControl> <ToolBar Style="{StaticResource controlStyle}"> <ToolBar.Items>5</ToolBar.Items> </ToolBar> <!--<InkCanvas Style="{StaticResource controlStyle}" />--> <TextBox Style="{StaticResource controlStyle}" Text="7" /> </StackPanel> </StackPanel> 

JpgValidationRule

 using System.Globalization; using System.IO; using System.Windows.Controls; namespace StylesDemo { public class JpgValidationRule : ValidationRule { public override ValidationResult Validate(object value, CultureInfo cultureInfo) { string fileName = value.ToString(); // Reject nonexistent files: if (!File.Exists(fileName)) return new ValidationResult(false, "Value is not a valid file!"); // Reject files that don't end in .jpg: if (Path.GetExtension(fileName).ToUpper() != ".JPG") return new ValidationResult(false, "Value is not a .jpg file!"); return new ValidationResult(true, null); } } } 

Answer 1

I think this is due to the default binding mode for TextBox.Text, which is TwoWay, and this path is required. You can try setting Mode="OneWay" as an attribute in the Binding tag, which should work here, but I'm not quite sure about your general requirement.