C # – WPF DataBinding verification is ignored

 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
 xmlns:x="http://schemas.microsoft.com/ winfx/2006/xaml"
 xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
 xmlns:d="http://schemas.microsoft.com/ expression/blend/2008" 
 xmlns:local="clr-namespace:Foo.Controls"
 mc:Ignorable="d" 
 d:DesignWidth="300">
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 < /Binding>
 
 
  
 
 
 
 
 

public class ScalarValidationRule: ValidationRule
{
 public override ValidationResult Validate(object value, CultureInfo cultureInfo)
 {
 string number = value as string; 
 double d;
 return new ValidationResult(Double.TryParse(numb er, NumberStyles.Any, cultureInfo, out d),
 String.Format("\"{0}\" is not a number.", number));
 }
}< /pre> 

I (believe) I am connecting data in a textbook way Binding validation, but it doesn’t work at all.

In the debugger, the Validate(object value, CultureInfo cultureInfo) method is never called.

What gives NS? Also, for bonus points, any pointers to debugging WPF would be great.

I posted my XAML and the course in question

 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
 xmlns:x="http://schemas.microsoft.com/ winfx/2006/xaml"
 xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
 xmlns:d="http://schemas.microsoft.com/ expression/blend/2008" 
 xmlns:local="clr-namespace:Foo.Controls"
 mc:Ignorable="d" 
 d:DesignWidth="300">
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 < /Binding>
 
 
  
 
 
 
 
 

Validity rules

< p>

public class ScalarValidationRule: ValidationRule
{
 public override ValidationResult Validate(object value, CultureInfo cultureInfo)
 {
 string number = value as string; 
 double d;
 return new ValidationResult(Double.TryParse(number, Nu mberStyles.Any, cultureInfo, out d),
 String.Format("\"{0}\" is not a number.", number));
 }
}

You are adding a ValidationRule to a one-way binding. One-way binding never pushes the value to the source, so there is no need to validate anything, and never Call ValidationRule. If you want to validate the data entered by the user, please set Mode = "TwoWay" on the binding. You can also omit the Mode attribute completely, because TextBox.Text is bound to two-way by default.

If you really need one-way binding and want to validate when the value is pushed from the source (Scalar) to the target (TextBox.Text), then set ValidatesOnTargetUpdated to True on the ValidationRule. You can either in XAML or in ValidationRule Do this in the constructor of the class.