1. introduction
在.NET开发领域，FluentValidation以其优雅、易扩展的特性成为开发者进行属性验证的首选工具。它不仅适用于Web开发，如MVC、Web API和ASP.NET CORE，同样也能完美集成在WPF应用程序中，提供强大的数据验证功能。本文将深入探讨如何在C# WPF项目中运用FluentValidation进行属性验证，并展示如何通过MVVM模式实现这一功能。
2. Function overview
Our goal is to build a WPF application that enables the following verification functions through FluentValidation:
- Verify the basic data type attributes of the ViewModel layer, such as int, string, etc.
- Verify complex properties in the ViewModel, including sub-properties of object properties as well as collection properties.
- Provides two intuitive error prompt styles to enhance the user experience.
Let's first look at the implementation renderings:
3. Problem solving and exploration
During the research process, I found that the official FluentValidation document mainly focuses on the verification of Web applications. For verification of WPF and complex attributes, official documentation provides limited examples. However, through in-depth research and practice, I found an effective way to use FluentValidation with WPF, especially for verification of complex attributes.
4. development steps
4.1. Create projects and introduce libraries
首先，创建一个新的WPF项目，并引入FluentValidation库用于属性验证，以及Prism.Wpf库以简化MVVM模式的实现。
<ItemGroup>
<PackageReference Include="FluentValidation" Version="11.9.0" />
<PackageReference Include="Prism.Wpf" Version="9.0.271-pre" />
</ItemGroup>
4.2. create entity classes
I created two entity classes: Student and Field, which represent object properties and collection item properties respectively. Both classes implement the IDataErrorInfo interface:
IDataErrorInfo接口常用于提供实体数据验证的错误信息。这个接口包含两个成员：一个索引器（this[string columnName]）和一个Error属性。索引器用于按属性名称提供错误信息，而Error属性则用于提供整个实体的错误概述。- 两个实体类和另外在后面提及的ViewModel中也实现
IDataErrorInfo接口，并在this[string columnName]索引器和Error属性中使用FluentValidation来验证属性。
4.2.1. General Class- Student
The student class contains 5 attributes: name, age, zip code, minimum value and maximum value. The minimum value and maximum value involve association verification, that is, the maximum value verification is notified after the minimum value changes, and vice versa.
/// <summary>
/// 学生实体
/// 继承BindableBase,即继承属性变化接口INotifyPropertyChanged
/// 实现IDataErrorInfo接口，用于FluentValidation验证，必须实现此接口
/// </summary>
public class Student : BindableBase, IDataErrorInfo
{
private int _age;
private string? _name;
private string? _zip;
private readonly StudentValidator _validator = new();
public string? Name
{
get => _name;
set => SetProperty(ref _name, value);
}
public int Age
{
get => _age;
set => SetProperty(ref _age, value);
}
public string? Zip
{
get => _zip;
set => SetProperty(ref _zip, value);
}
private int _minValue;
public int MinValue
{
get => _minValue;
set
{
SetProperty(ref _minValue, value);
// 关联更新最大值验证
RaisePropertyChanged(nameof(MaxValue));
}
}
private int _maxValue;
public int MaxValue
{
get => _maxValue;
set
{
SetProperty(ref _maxValue, value);
// 关联更新最小值验证
RaisePropertyChanged(nameof(MinValue));
}
}
public string this[string columnName]
{
get
{
var validateResult = _validator.Validate(this);
if (validateResult.IsValid)
{
return string.Empty;
}
var firstOrDefault =
validateResult.Errors.FirstOrDefault(error => error.PropertyName == columnName);
return firstOrDefault == null ? string.Empty : firstOrDefault.ErrorMessage;
}
}
public string Error
{
get
{
var validateResult = _validator.Validate(this);
if (validateResult.IsValid)
{
return string.Empty;
}
var errors = string.Join(Environment.NewLine, validateResult.Errors.Select(x => x.ErrorMessage).ToArray());
return errors;
}
}
}
上面关键代码在public string this[string columnName]：这里进行输入表单项的数据校验，FluentValidation调用就在这里，校验逻辑封装在StudentValidator，表单输入时会实时调用该处代码，columnName表示表单项的列名，就是View绑定的属性名。
4.2.2. Set class- Field
This class is used as a collection item in ViewModel to simulate dynamic form data verification. It simply contains four attributes: field name, field display name, data type, and data value. The form mainly verifies whether the input data value is legal based on the data type. Similarly, this entity needs to inherit the IDataErrorInfo interface to trigger FluentValidation verification.
/// <summary>
/// 扩展字段，用于生成动态表单
/// 继承BindableBase,即继承属性变化接口INotifyPropertyChanged
/// 实现IDataErrorInfo接口，用于FluentValidation验证，必须实现此接口
/// </summary>
public class Field : BindableBase, IDataErrorInfo
{
private string? _value;
private readonly FieldValidator _validator = new();
public Field(DataType type, string typeLabel, string name, string value)
{
Type = type;
TypeLabel = typeLabel;
Name = name;
Value = value;
}
/// <summary>
/// 数据类型
/// </summary>
public DataType Type { get; set; }
/// <summary>
/// 数据类型名称
/// </summary>
public string TypeLabel { get; set; }
/// <summary>
/// 名称
/// </summary>
public string Name { get; set; }
/// <summary>
/// 值
/// </summary>
public string? Value
{
get => _value;
set => SetProperty(ref _value, value);
}
public string this[string columnName]
{
get
{
var validateResult = _validator.Validate(this);
if (validateResult.IsValid)
{
return string.Empty;
}
var firstOrDefault =
validateResult.Errors.FirstOrDefault(error => error.PropertyName == columnName);
return firstOrDefault == null ? string.Empty : firstOrDefault.ErrorMessage;
}
}
public string Error
{
get
{
var validateResult = _validator.Validate(this);
if (validateResult.IsValid)
{
return string.Empty;
}
var errors = string.Join(Environment.NewLine, validateResult.Errors.Select(x => x.ErrorMessage).ToArray());
return errors;
}
}
}
public enum DataType
{
Text,
Number,
Date
}
看上面代码，public string this[string columnName]代码处写法和Student类一样，只是_validator变量类型不同，前者为StudentValidator，这里是FieldValidator，下面我们看看这两个类怎么写。
4.3. Create a validator
对于每个实体类，我都创建了一个对应的验证器类：StudentValidator和FieldValidator。这些验证器类继承自AbstractValidator，并在其中定义了验证规则。验证属性的写法有两种：
You can add features above the entity attributes (this article does not specifically explain it, Baidu articles introduce a lot);
Add it in the form of code, as shown below, to create a validator class that inherits from AbstractValidator. Write rule verification attributes in this validator constructor for easy management.
本文使用第二种，下面通过创建StudentValidator和FieldValidator两个验证器类介绍。
4.3.1. StudentValidator
这是学生验证器StudentValidator，需要继承AbstractValidator，泛型指定前面需要验证的实体类Student：
public class StudentValidator : AbstractValidator<Student>
{
public StudentValidator()
{
RuleFor(vm => vm.Name)
.NotEmpty()
.WithMessage("请输入学生姓名！")
.Length(5, 30)
.WithMessage("学生姓名长度限制在5到30个字符之间！");
RuleFor(vm => vm.Age)
.GreaterThanOrEqualTo(0)
.WithMessage("学生年龄为整数！")
.ExclusiveBetween(10, 150)
.WithMessage("请正确输入学生年龄(10-150)");
_ = RuleFor(vm => vm.Zip)
.NotEmpty()
.WithMessage("邮政编码不能为空！")
.Must(BeAValidZip)
.WithMessage("邮政编码由六位数字组成。");
RuleFor(model => model.MinValue).Must((model, minValue) => minValue < model.MaxValue).WithMessage("最小值应该小于最大值");
RuleFor(model => model.MaxValue).Must((model, maxValue) => maxValue > model.MinValue).WithMessage("最大值应该大于最小值");
}
private static bool BeAValidZip(string? zip)
{
if (string.IsNullOrEmpty(zip))
{
return false;
}
var regex = new Regex(@"\d{6}");
return regex.IsMatch(zip);
}
}
代码简单，使用到数字的大小和范围验证（见Age）、字符串不能为空和长度限制（见Name）、字符串正则表达式验证（见Zip）、多属性关联验证（最小值和最大值，这里配合属性set时通知其他属性验证通知RaisePropertyChanged(nameof(MaxValue));）。
4.3.2. FieldValidator
动态表单数据值校验器，同理需要继承AbstractValidator，泛型指定前面需要验证的实体类Field：：
public class FieldValidator : AbstractValidator<Field>
{
public FieldValidator()
{
RuleFor(field => field.Value)
.Must((field, value) => (field.Type == DataType.Text && !string.IsNullOrWhiteSpace(value))
|| (field.Type == DataType.Number && double.TryParse(value, out _))
|| (field.Type == DataType.Date && DateTime.TryParse(value, out _)))
.WithMessage("1.文本不能为空；2.数字类型请填写数字；3.日志类型请填写日期类型");
}
}
It's a little simpler here:
- Text data type, value cannot be empty;
- 数字数据类型，必须是
double类型； - 日期类型，必须能使用
DateTime转换；
本文只做简单演示，多种数据类型放Must方法中做统一验证，验证出错给出统一的提示信息，读者可按实际情况修改。
4.3.3. StudentViewModelValidator
此外，我还创建了一个StudentViewModelValidator，用于验证ViewModel层的属性。这个验证器能够处理基本数据类型、对象属性以及集合属性的验证。
public class StudentViewModelValidator : AbstractValidator<StudentViewModel>
{
public StudentViewModelValidator()
{
RuleFor(vm => vm.Title)
.NotEmpty()
.WithMessage("标题长度不能为空！")
.Length(5, 30)
.WithMessage("标题长度限制在5到30个字符之间！");
RuleFor(vm => vm.CurrentStudent).SetValidator(new StudentValidator());
RuleForEach(vm => vm.Fields).SetValidator(new FieldValidator());
}
}
Title用于关联验证基本数据类型(string类型)；CurrentStudent用于验证对象属性（Student类的实例），设置验证该属性时使用StudentValidator验证器；Fields用于验证集合属性(ObservableCollection<Field>)，设置验证该属性子项时使用FieldValidator验证器，注意前面使用的RuleForEach表示关联集合中的项验证器。
4.4. ViewModel Layer Implementation
StudentViewModel与Student实体类结构类似，都需要实现IDataErrorInfo接口，该类由一个简单的string属性(Title)和一个复杂的Student对象属性(CurrentStudent)、集合属性ObservableCollection<Field> Fields组成，代码如下：
/// <summary>
/// 视图ViewModel
/// 继承BindableBase,即继承属性变化接口INotifyPropertyChanged
/// 实现IDataErrorInfo接口，用于FluentValidation验证，必须实现此接口
/// </summary>
public class StudentViewModel : BindableBase, IDataErrorInfo
{
private Student _currentStudent;
private string _title;
private readonly StudentViewModelValidator _validator;
public string Title
{
get => _title;
set => SetProperty(ref _title, value);
}
public Student CurrentStudent
{
get => _currentStudent;
set => SetProperty(ref _currentStudent, value);
}
public ObservableCollection<Field> Fields { get; } = new();
private DelegateCommand _saveCommand;
public DelegateCommand SaveCommand => _saveCommand ??= new DelegateCommand(HandleSaveCommand,
HandleCanExecuteSaveCommand);
private DelegateCommand _cancelCommand;
public DelegateCommand CancelCommand =>
_cancelCommand ??= new DelegateCommand(HandleCancelCommand, () => true);
public StudentViewModel()
{
_validator = new StudentViewModelValidator();
CurrentStudent = new Student
{
Name = "李刚的儿",
Age = 23
};
Fields.Add(new Field(DataType.Text, "文本，比如：四川省成都市场", "地址", ""));
Fields.Add(new Field(DataType.Number, "数字，比如：12", "工龄", ""));
Fields.Add(new Field(DataType.Date, "时间，比如：2023-09-26 05:13:23", "培训时间", ""));
PropertyChanged += Validate;
CurrentStudent.PropertyChanged += Validate;
foreach (var field in Fields)
{
field.PropertyChanged += Validate;
}
}
~StudentViewModel()
{
PropertyChanged -= Validate;
CurrentStudent.PropertyChanged -= Validate;
foreach (var field in Fields)
{
field.PropertyChanged -= Validate;
}
}
private void Validate(object sender, PropertyChangedEventArgs e)
{
_isCanExecuteSaveCommand = _validator.Validate(this).IsValid;
SaveCommand.RaiseCanExecuteChanged();
}
private void HandleSaveCommand()
{
var validateResult = _validator.Validate(this);
if (validateResult.IsValid)
{
MessageBox.Show("看到我说明验证成功！");
}
else
{
var errorMsg = string.Join(Environment.NewLine,
validateResult.Errors.Select(x => x.ErrorMessage).ToArray());
MessageBox.Show($"慌啥子嘛，你再检查下输入噻：\r\n{errorMsg}");
}
}
private bool _isCanExecuteSaveCommand;
private bool HandleCanExecuteSaveCommand()
{
return _isCanExecuteSaveCommand;
}
private void HandleCancelCommand()
{
MessageBox.Show("我啥都不做，退休了");
}
public string this[string columnName]
{
get
{
var validateResult = _validator.Validate(this);
if (validateResult.IsValid)
{
return string.Empty;
}
var firstOrDefault =
validateResult.Errors.FirstOrDefault(error => error.PropertyName == columnName);
return firstOrDefault == null ? string.Empty : firstOrDefault.ErrorMessage;
}
}
public string Error
{
get
{
var validateResult = _validator.Validate(this);
if (validateResult.IsValid)
{
return string.Empty;
}
var errors = string.Join(Environment.NewLine, validateResult.Errors.Select(x => x.ErrorMessage).ToArray());
return errors;
}
}
}
ViewModel属性验证和Student及Field类似，这里我加上了保存(SaveCommand)和取消(CancelCommand)两个命令，其中保存命令需要所有属性验证通过才可用，通过注册属性的变化事件PropertyChanged，在变化事件处理程序中验证：
PropertyChanged += Validate;
CurrentStudent.PropertyChanged += Validate;
foreach (var field in Fields)
{
field.PropertyChanged += Validate;
}
private void Validate(object sender, PropertyChangedEventArgs e)
{
_isCanExecuteSaveCommand = _validator.Validate(this).IsValid;
SaveCommand.RaiseCanExecuteChanged();
}
4.5. View Layer Implementation
在视图层，我创建了一个用户控件StudentView，用于显示输入表单和验证结果。通过绑定ViewModel层的属性和命令，视图层能够与ViewModel层进行交互，并实时显示验证错误。这里比较简单，提供简单属性标题(Title)、复杂属性(包括学生姓名(CurrentStudent.Name)、学生年龄( CurrentStudent .Age)、学生邮政编码( CurrentStudent .Zip)、最小值(CurrentStudent.MinValue)、最大值(CurrentStudent.MaxValue)）验证、集合属性验证(Fields)，xaml代码如下：
<UserControl
x:Class="WpfFluentValidation.Views.StudentView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:models="clr-namespace:WpfFluentValidation.Models"
xmlns:vm="clr-namespace:WpfFluentValidation.ViewModels"
mc:Ignorable="d" Padding="10">
<UserControl.DataContext>
<vm:StudentViewModel />
</UserControl.DataContext>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="*" />
<RowDefinition Height="50" />
</Grid.RowDefinitions>
<ScrollViewer HorizontalScrollBarVisibility="Hidden" VerticalScrollBarVisibility="Auto">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<GroupBox Header="ViewModel直接属性验证">
<StackPanel>
<Label Content="标题：" />
<TextBox Style="{StaticResource Styles.TextBox.ErrorStyle1}"
Text="{Binding Title, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />
</StackPanel>
</GroupBox>
<GroupBox Grid.Row="1" Header="ViewModel对象属性CurrentStudent的属性验证">
<StackPanel>
<StackPanel>
<Label Content="姓名：" />
<TextBox Style="{StaticResource Styles.TextBox.ErrorStyle2}"
Text="{Binding CurrentStudent.Name, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />
</StackPanel>
<StackPanel>
<Label Content="年龄：" />
<TextBox Style="{StaticResource Styles.TextBox.ErrorStyle2}"
Text="{Binding CurrentStudent.Age, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />
</StackPanel>
<StackPanel>
<Label Content="邮编：" />
<TextBox Style="{StaticResource Styles.TextBox.ErrorStyle2}"
Text="{Binding CurrentStudent.Zip, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />
</StackPanel>
<StackPanel>
<Label Content="最小值：" />
<TextBox Style="{StaticResource Styles.TextBox.ErrorStyle2}"
Text="{Binding CurrentStudent.MinValue, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />
</StackPanel>
<StackPanel>
<Label Content="最大值：" />
<TextBox Style="{StaticResource Styles.TextBox.ErrorStyle2}"
Text="{Binding CurrentStudent.MaxValue, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />
</StackPanel>
</StackPanel>
</GroupBox>
<GroupBox Grid.Row="2" Header="ViewModel集合属性Fields的属性验证">
<ItemsControl ItemsSource="{Binding Fields}">
<ItemsControl.ItemTemplate>
<DataTemplate DataType="{x:Type models:Field}">
<Border Padding="10">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<TextBlock Margin="0,0,0,5">
<Run Text="{Binding Name}" />
<Run Text="(" />
<Run Text="{Binding TypeLabel}" />
<Run Text=")" />
</TextBlock>
<TextBox Grid.Row="1" Style="{StaticResource Styles.TextBox.ErrorStyle2}"
Text="{Binding Value, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />
</Grid>
</Border>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</GroupBox>
</Grid>
</ScrollViewer>
<StackPanel Grid.Row="1" HorizontalAlignment="Right" Orientation="Horizontal">
<Button Content="取消" Command="{Binding CancelCommand}" Style="{StaticResource Styles.Button.Common}"
Margin="0 3 40 3" />
<Button Content="提交" Command="{Binding SaveCommand}" Style="{StaticResource Styles.Button.Blue}"
Margin="0 3 10 3" />
</StackPanel>
</Grid>
</UserControl>
4.6. Error prompt style
In order to improve the user experience, I have defined two error prompt styles: one is to prompt errors next to the input box through a red icon, and the other is to display error text on the right side of the input box. These styles are defined in App.xaml and can be reused throughout the application.
<Application
x:Class="WpfFluentValidation.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
StartupUri="MainWindow.xaml">
<Application.Resources>
<Style TargetType="StackPanel">
<Setter Property="Margin" Value="0,5" />
</Style>
<!-- 第一种错误样式，红色边框 -->
<Style x:Key="Styles.TextBox.ErrorStyle1" TargetType="{x:Type TextBox}">
<Setter Property="Width" Value="250" />
<Setter Property="Height" Value="25" />
<Setter Property="HorizontalAlignment" Value="Left" />
<Setter Property="Validation.ErrorTemplate">
<Setter.Value>
<ControlTemplate>
<DockPanel>
<Grid
Width="16"
Height="16"
Margin="3,0,0,0"
VerticalAlignment="Center"
DockPanel.Dock="Right">
<Ellipse
Width="16"
Height="16"
Fill="Red" />
<Ellipse
Width="3"
Height="8"
Margin="0,2,0,0"
HorizontalAlignment="Center"
VerticalAlignment="Top"
Fill="White" />
<Ellipse
Width="2"
Height="2"
Margin="0,0,0,2"
HorizontalAlignment="Center"
VerticalAlignment="Bottom"
Fill="White" />
</Grid>
<Border
BorderBrush="Red"
BorderThickness="2"
CornerRadius="2">
<AdornedElementPlaceholder />
</Border>
</DockPanel>
</ControlTemplate>
</Setter.Value>
</Setter>
<Style.Triggers>
<Trigger Property="Validation.HasError" Value="true">
<Setter Property="ToolTip"
Value="{Binding RelativeSource={x:Static RelativeSource.Self}, Path=(Validation.Errors)[0].ErrorContent}" />
</Trigger>
</Style.Triggers>
</Style>
<!-- 第二种错误样式，右键文字提示 -->
<Style x:Key="Styles.TextBox.ErrorStyle2" TargetType="{x:Type TextBox}">
<Setter Property="Width" Value="250" />
<Setter Property="Height" Value="25" />
<Setter Property="VerticalContentAlignment" Value="Center" />
<Setter Property="Padding" Value="5,0" />
<Setter Property="HorizontalAlignment" Value="Left" />
<Setter Property="Validation.ErrorTemplate">
<Setter.Value>
<ControlTemplate>
<StackPanel Orientation="Horizontal">
<AdornedElementPlaceholder x:Name="textBox" />
<Grid>
<TextBlock Margin="10 0 0 0" Width="130"
Foreground="Red" TextWrapping="Wrap"
Text="{Binding [0].ErrorContent}" />
</Grid>
</StackPanel>
</ControlTemplate>
</Setter.Value>
</Setter>
<Style.Triggers>
<Trigger Property="Validation.HasError" Value="true">
<Setter Property="ToolTip"
Value="{Binding RelativeSource={x:Static RelativeSource.Self}, Path=(Validation.Errors)[0].ErrorContent}" />
<Setter Property="Background" Value="LightPink" />
<Setter Property="BorderBrush" Value="Red" />
<Setter Property="Foreground" Value="White" />
</Trigger>
</Style.Triggers>
</Style>
<Style TargetType="GroupBox">
<Setter Property="Margin" Value="5" />
<Setter Property="Padding" Value="2" />
<Setter Property="BorderBrush" Value="#FF0078D7" />
<Setter Property="BorderThickness" Value="2" />
<Setter Property="Background" Value="#FFF0F0F0" />
<Setter Property="Foreground" Value="#FF0078D7" />
<Setter Property="FontWeight" Value="Bold" />
</Style>
<Style x:Key="Styles.Button.Common" TargetType="{x:Type Button}">
<Setter Property="MinWidth" Value="75" />
<Setter Property="MinHeight" Value="25" />
<Setter Property="Background" Value="White" />
<Setter Property="Foreground" Value="Black" />
</Style>
<Style
x:Key="Styles.Button.Blue"
BasedOn="{StaticResource ResourceKey=Styles.Button.Common}"
TargetType="{x:Type Button}">
<Setter Property="Background" Value="Green" />
<Setter Property="Foreground" Value="White" />
</Style>
</Application.Resources>
</Application>
5. effect display
Through the implementation of the above steps, we get a fully functional WPF application. It enables real-time verification based on user input and provides intuitive error prompts. When all attributes have been verified, the Submit button becomes available.
6. Source code sharing
In order to facilitate readers to learn and communicate, this article synchronizes all code to Gitee and GitHub platforms. Interested developers are welcome to visit the following link to obtain the source code:
- gitee: https://gitee.com/dotnet9/FluentValidationForWpf
- github： https://github.com/dotnet9/FluentValidationForWPF
7. summary
Through the introduction and practice of this article, we successfully applied FluentValidation to the C#WPF project and achieved comprehensive verification of ViewModel layer attributes. This not only improves the security and accuracy of data, but also provides users with a better interactive experience. I hope this article can provide useful reference and inspiration for developers to use FluentValidation in WPF projects.
Reference:
- FluentValidation official website: https://fluentvalidation.net/