值必须提交到对象中,因为IDataErrorInfo仅使用propertyName检索特定属性的错误。无法将建议的值(应该进行验证)传递给它,因此只能使用已提交的属性值。
我认为这是一个很好的方法,因为视图模型和视图始终保持同步,即使属性具有无效值,也会在视图模型中保留无效值状态,因此可以在视图模型中包含基于该信息的其他逻辑,而不是视图。
如果您想将建议的值验证传播到视图模型,则必须使用自己的自定义接口和验证规则来完成。
以下是我完成的方式:
IProposedValueErrorInfo.cs
using System.Globalization;
namespace WpfApplication
{
public interface IProposedValueErrorInfo
{
object GetError(string propertyName, object value, CultureInfo cultureInfo);
}
}
ProposedValueErrorValidationRule.cs
using System;
using System.Globalization;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
namespace WpfApplication
{
internal sealed class ProposedValueErrorValidationRule : ValidationRule
{
private readonly DependencyObject targetObject;
private readonly DependencyProperty targetProperty;
public ProposedValueErrorValidationRule(DependencyObject targetObject, DependencyProperty targetProperty)
: base(ValidationStep.RawProposedValue, true)
{
if (targetObject == null)
throw new ArgumentNullException("targetObject");
if (targetProperty == null)
throw new ArgumentNullException("targetProperty");
this.targetObject = targetObject;
this.targetProperty = targetProperty;
}
public override ValidationResult Validate(object value, CultureInfo cultureInfo)
{
var expression = BindingOperations.GetBindingExpression(this.targetObject, this.targetProperty);
if (expression != null)
{
var sourceItem = expression.DataItem as IProposedValueErrorInfo;
if (sourceItem != null)
{
var propertyName = expression.ParentBinding.Path != null ? expression.ParentBinding.Path.Path : null;
if (propertyName != null)
{
var error = sourceItem.GetError(propertyName, value, cultureInfo);
if (error != null)
return new ValidationResult(false, error);
}
}
}
return ValidationResult.ValidResult;
}
}
}
ProposedValueValidationBindingExtension.cs
using System;
using System.Windows;
using System.Windows.Data;
using System.Windows.Markup;
namespace WpfApplication
{
public sealed class ProposedValueValidationBindingExtension : MarkupExtension
{
private readonly Binding binding;
public ProposedValueValidationBindingExtension(Binding binding)
{
if (binding == null)
throw new ArgumentNullException("binding");
this.binding = binding;
}
public override object ProvideValue(IServiceProvider serviceProvider)
{
var provideValueTarget = serviceProvider != null ? serviceProvider.GetService(typeof(IProvideValueTarget)) as IProvideValueTarget : null;
if (provideValueTarget != null)
this.binding.ValidationRules.Add(new ProposedValueErrorValidationRule(provideValueTarget.TargetObject as DependencyObject, provideValueTarget.TargetProperty as DependencyProperty));
return this.binding.ProvideValue(serviceProvider);
}
}
}
Person.cs
using System.Globalization;
namespace WpfApplication
{
public class Person : IProposedValueErrorInfo
{
public int Age { get; set; }
public string Surname { get; set; }
#region IProposedValueErrorInfo Members
object IProposedValueErrorInfo.GetError(string propertyName, object value, CultureInfo cultureInfo)
{
switch (propertyName)
{
case "Age":
int dummy;
return value is int || int.TryParse(value as string, NumberStyles.Integer, cultureInfo, out dummy) ? null : "Age must be a number.";
}
return null;
}
#endregion
}
}
MainWindow.xaml
<Window x:Class="WpfApplication.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:WpfApplication"
Title="MainWindow" Height="350" Width="525">
<Window.DataContext>
<local:Person Age="16"/>
</Window.DataContext>
<StackPanel>
<TextBox Text="{local:ProposedValueValidationBinding {Binding Age}}" ToolTip="{Binding Path='(Validation.Errors)/ErrorContent', RelativeSource={RelativeSource Self}}"/>
<TextBox Text="{local:ProposedValueValidationBinding {Binding Age}}" ToolTip="{Binding Path='(Validation.Errors)/ErrorContent', RelativeSource={RelativeSource Self}}"/>
</StackPanel>
</Window>