I am adding a validation rule to a textbox (following examples on WPF 4 Unleashed by Adam Nathan)
When starting an application, I am faced with the following cryptic error message
Provide value on 'System.Windows.Data.Binding' threw an exception
What does the error mean and what needs to be done to address the problem?
Here is the full 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);
}
}
}