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WPF提供了能与数据绑定系统紧密协作的验证功能。提供了两种方法用于捕获非法值：
1、可在数据对象中引发错误。
可以在设置属性时抛出异常，通常WPF会忽略所有在设置属性时抛出的异常，但可以进行配置，从而显示更有帮助的可视化指示。另一种选择是在自定义的数据类中实现 INotifyDataErrorInfo 或 IDataErrorInfo 接口，从而可得到指示错误的功能而不会抛出异常。
2、可在绑定级别上定义验证。
这种方法可获得使用相同验证的灵活性，而不必考虑使用的是哪个控件。更好的是，因为是在不同类中定义验证，可以很容易的在存储类似数据类型的多个绑定中重用验证。
错误模板
错误模板使用的是装饰层，装饰层是位于普通窗口内容之上的绘图层。使用装饰层，可添加可视化装饰来指示错误，而不用替换控件背后的控件模板或改变窗口的布局。文本框的标准错误模板通过在相应文本框的上面添加红色的Border元素来指示发生了错误。可使用错误模板添加其他细节。
<Style TargetType="{x:Type TextBox}"><Setter Property="Validation.ErrorTemplate"><Setter.Value><ControlTemplate><DockPanel LastChildFill="True"><TextBlock DockPanel.Dock="Right" Foreground="Red" FontSize="14" FontWeight="Bold" ToolTip="{Binding ElementName=adornerPlaceholder, Path=AdornedElement.(Validation.Errors)[0].ErrorContent}">*</TextBlock><Border BorderBrush="Green" BorderThickness="1"><AdornedElementPlaceholder Name="adornerPlaceholder"></AdornedElementPlaceholder></Border></DockPanel></ControlTemplate></Setter.Value></Setter><Style.Triggers><Trigger Property="Validation.HasError" Value="true"><Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}"/></Trigger></Style.Triggers>
</Style>在数据对象中引发错误
我这里分别尝试了 IDataErrorInfo 与 INotifyDataErrorInfo 接口，这俩需要分别对应使用 <DataErrorValidationRule/> 与 <NotifyDataErrorValidationRule/> 。
IDataErrorInfo 接口定义了Error字段，这个字段在结构有多个字段时，难以映射，于是在[]下标下实现逻辑。
INotifyDataErrorInfo 接口需要实现 HasError，GetErrors 两个函数，并需要在属性的set 访问器内实现校验逻辑，并管理Error信息。
总体来说，在数据对象中引发错误不是一个好选择，验证逻辑硬编码在数据对象中，不利于复用。
在绑定级别上定义验证
在绑定级别上定义验证是针对于数据类型自定义验证规则，可以对同一种数据类型进行复用。自定义验证规则需要继承自 ValidationRule 类，需要实现 Validate 函数，在其中完成自定义验证内容。
public class PriceRule : ValidationRule
{private decimal min = 0;private decimal max = decimal.MaxValue;public decimal Min{get => min;set => min = value;}public decimal Max{get => max;set => max = value;}public override ValidationResult Validate(object value, CultureInfo cultureInfo){decimal price = 0;try{if (((string)value).Length > 0){price = Decimal.Parse((string)value, NumberStyles.Any, cultureInfo);}}catch{return new ValidationResult(false, "Illegal characters.");}if (price < min || price > max){return new ValidationResult(false, "Not in the range " + Min + " to " + Max + ".");}else{return new ValidationResult(true, null);}}
}验证多个值
如果需要执行对两个或更多个绑定值的验证，可以通过 BindingGroup 来实现，将需要校验的多个控件放置于同一个容器中，在容器级别应用验证规则，需要通过事件主动触发验证，通常是子组件失去焦点时。
<Grid Grid.Row="3" Grid.ColumnSpan="2" DataContext="{Binding Path=Person}" TextBoxBase.LostFocus="Grid_LostFocus"><Grid.ColumnDefinitions><ColumnDefinition/><ColumnDefinition/></Grid.ColumnDefinitions><Grid.RowDefinitions><RowDefinition/><RowDefinition/></Grid.RowDefinitions><Grid.BindingGroup><BindingGroup x:Name="personValidation"><BindingGroup.ValidationRules><local:PersonRule/></BindingGroup.ValidationRules></BindingGroup></Grid.BindingGroup><TextBlock Grid.Row="0" Grid.Column="0">Person ID:</TextBlock><TextBox Grid.Row="0" Grid.Column="1" Text="{Binding Path=ID}" /><TextBlock Grid.Row="1" Grid.Column="0">Person Name:</TextBlock><TextBox Grid.Row="1" Grid.Column="1" Text="{Binding Path=Name}"/>
</Grid>public class Person : ViewModelBase
{private string name = string.Empty;public string Name { get=>name; set=> SetProperty(ref name, value); }private string id = string.Empty;public string ID { get => id; set => SetProperty(ref id, value); }
}
public class PersonRule : ValidationRule
{public override ValidationResult Validate(object value, CultureInfo cultureInfo){BindingGroup bindingGroup = (BindingGroup)value;Person? person = bindingGroup.Items[0] as Person;string name = (string)bindingGroup.GetValue(person, "Name");string id = (string)bindingGroup.GetValue(person, "ID");if ((name == "") && (id == "")){return new ValidationResult(false, "A Person requires a ID or Name.");}else{return new ValidationResult(true, null);}}
}下面贴出完整的测试代码：
MainWindow.xaml
<Window x:Class="TestValidation.MainWindow"xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"xmlns:d="http://schemas.microsoft.com/expression/blend/2008"xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"xmlns:local="clr-namespace:TestValidation"mc:Ignorable="d"Title="MainWindow" Height="450" Width="800"><Border Padding="7" Margin="7" Background="LightSteelBlue"><Grid x:Name="myGrid"><Grid.Resources><Style TargetType="{x:Type TextBox}"><Setter Property="Validation.ErrorTemplate"><Setter.Value><ControlTemplate><DockPanel LastChildFill="True"><TextBlock DockPanel.Dock="Right" Foreground="Red" FontSize="14" FontWeight="Bold" ToolTip="{Binding ElementName=adornerPlaceholder, Path=AdornedElement.(Validation.Errors)[0].ErrorContent}">*</TextBlock><Border BorderBrush="Green" BorderThickness="1"><AdornedElementPlaceholder Name="adornerPlaceholder"></AdornedElementPlaceholder></Border></DockPanel></ControlTemplate></Setter.Value></Setter><Style.Triggers><Trigger Property="Validation.HasError" Value="true"><Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}"/></Trigger></Style.Triggers></Style></Grid.Resources><Grid.ColumnDefinitions><ColumnDefinition Width="Auto"/><ColumnDefinition/></Grid.ColumnDefinitions><Grid.RowDefinitions><RowDefinition Height="*"/><RowDefinition Height="*"/><RowDefinition Height="*"/><RowDefinition Height="2*"/></Grid.RowDefinitions><TextBlock Grid.Row="0" Grid.Column="0">PersonAge:</TextBlock><TextBox Grid.Row="0" Grid.Column="1" DataContext="{Binding Path=PersonAge}"><TextBox.Text><Binding Path="Age" NotifyOnValidationError="true"><Binding.ValidationRules><DataErrorValidationRule/></Binding.ValidationRules></Binding></TextBox.Text></TextBox><TextBlock Grid.Row="1" Grid.Column="0">PersonName:</TextBlock><TextBox Grid.Row="1" Grid.Column="1" DataContext="{Binding Path=PersonName}"><TextBox.Text><Binding Path="Name" NotifyOnValidationError="true"><Binding.ValidationRules><NotifyDataErrorValidationRule/></Binding.ValidationRules></Binding></TextBox.Text></TextBox><TextBlock Grid.Row="2" Grid.Column="0">PersonPrice:</TextBlock><TextBox Grid.Row="2" Grid.Column="1" DataContext="{Binding Path=PersonPrice}"><TextBox.Text><Binding Path="Price" NotifyOnValidationError="true"><Binding.ValidationRules><local:PriceRule Min="0"/></Binding.ValidationRules></Binding></TextBox.Text></TextBox><Grid Grid.Row="3" Grid.ColumnSpan="2" DataContext="{Binding Path=Person}" TextBoxBase.LostFocus="Grid_LostFocus"><Grid.ColumnDefinitions><ColumnDefinition/><ColumnDefinition/></Grid.ColumnDefinitions><Grid.RowDefinitions><RowDefinition/><RowDefinition/></Grid.RowDefinitions><Grid.BindingGroup><BindingGroup x:Name="personValidation"><BindingGroup.ValidationRules><local:PersonRule/></BindingGroup.ValidationRules></BindingGroup></Grid.BindingGroup><TextBlock Grid.Row="0" Grid.Column="0">Person ID:</TextBlock><TextBox Grid.Row="0" Grid.Column="1" Text="{Binding Path=ID}" /><TextBlock Grid.Row="1" Grid.Column="0">Person Name:</TextBlock><TextBox Grid.Row="1" Grid.Column="1" Text="{Binding Path=Name}"/></Grid></Grid></Border>
</Window>
MainWindow.xaml.cs
using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Globalization;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;namespace TestValidation;public class ViewModelBase : INotifyPropertyChanged
{public event PropertyChangedEventHandler? PropertyChanged;protected virtual void OnPropertyChanged([CallerMemberName] string? propertyName = null){PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));}protected virtual bool SetProperty<T>(ref T member, T value, [CallerMemberName] string? propertyName = null){if (EqualityComparer<T>.Default.Equals(member, value)){return false;}member = value;OnPropertyChanged(propertyName);return true;}
}
public class PersonAge : ViewModelBase, IDataErrorInfo
{public string this[string columnName]{get{if(columnName == "Age"){if(Age < 0 || Age > 150){return "Age must not be less than 0 or greater than 150.";}}return null;}}private int age;public int Age { get => age; set => SetProperty(ref age, value); }public string Error => null;
}
public class PersonName : ViewModelBase, INotifyDataErrorInfo
{private string name = string.Empty;public string Name {get => name;set{bool valid = true;foreach (char c in value){if (!char.IsLetterOrDigit(c)){valid = false;break;}}if(!valid){List<string> errors = new List<string> ();errors.Add("The Name can only contain letters and numbers.");SetErrors("Name", errors);}else{ClearErrors("Name");}SetProperty(ref name, value);}}private Dictionary<string, List<string>> errors = new Dictionary<string, List<string>>();private void SetErrors(string propertyName, List<string> propertyErrors){errors.Remove(propertyName);errors.Add(propertyName, propertyErrors);if (ErrorsChanged != null)ErrorsChanged(this, new DataErrorsChangedEventArgs(propertyName));}private void ClearErrors(string propertyName){errors.Remove(propertyName);if(ErrorsChanged != null)ErrorsChanged(this, new DataErrorsChangedEventArgs(propertyName));}public bool HasErrors{get { return errors.Count > 0; }}public event EventHandler<DataErrorsChangedEventArgs>? ErrorsChanged;public IEnumerable GetErrors(string? propertyName){if(!string.IsNullOrEmpty(propertyName) && errors.ContainsKey(propertyName)){return errors[propertyName];}return new List<string>();}
}
public class PersonPrice : ViewModelBase, INotifyPropertyChanged
{private decimal price = 0;public decimal Price{get => price; set{SetProperty(ref price, value);}}
}public class PriceRule : ValidationRule
{private decimal min = 0;private decimal max = decimal.MaxValue;public decimal Min{get => min;set => min = value;}public decimal Max{get => max;set => max = value;}public override ValidationResult Validate(object value, CultureInfo cultureInfo){decimal price = 0;try{if (((string)value).Length > 0){price = Decimal.Parse((string)value, NumberStyles.Any, cultureInfo);}}catch{return new ValidationResult(false, "Illegal characters.");}if (price < min || price > max){return new ValidationResult(false, "Not in the range " + Min + " to " + Max + ".");}else{return new ValidationResult(true, null);}}
}public class Person : ViewModelBase
{private string name = string.Empty;public string Name { get=>name; set=> SetProperty(ref name, value); }private string id = string.Empty;public string ID { get => id; set => SetProperty(ref id, value); }
}
public class PersonRule : ValidationRule
{public override ValidationResult Validate(object value, CultureInfo cultureInfo){BindingGroup bindingGroup = (BindingGroup)value;Person? person = bindingGroup.Items[0] as Person;string name = (string)bindingGroup.GetValue(person, "Name");string id = (string)bindingGroup.GetValue(person, "ID");if ((name == "") && (id == "")){return new ValidationResult(false, "A Person requires a ID or Name.");}else{return new ValidationResult(true, null);}}
}
public partial class MainWindow : Window
{public MainWindow(){InitializeComponent();myGrid.DataContext = this;}public PersonAge PersonAge { get; set; } = new PersonAge();public PersonName PersonName { get; set; } = new PersonName();public PersonPrice PersonPrice { get; set; } = new PersonPrice();public Person Person { get; set; } = new Person();private void Grid_LostFocus(object sender, RoutedEventArgs e){personValidation.CommitEdit();}
}