如何从ViewModel中分离ViewModel属性验证？

Question

我正在使用MVVMLight。 这是我的Department模型/ POCO课程。 我不想以任何方式污染它。

 public partial class Department
    {
        public int DepartmentId { get; set; }
        public string DepartmentCode { get; set; }
        public string DepartmentFullName { get; set; }
    }

这是CreateDepartmentViewModel ：

public class CreateDepartmentViewModel : ViewModelBase
{
    private IDepartmentService departmentService;
    public RelayCommand CreateDepartmentCommand { get; private set; }

    public CreateDepartmentViewModel(IDepartmentService DepartmentService)
    {
        departmentService = DepartmentService;
        this.CreateDepartmentCommand = new RelayCommand(CreateDepartment, CanExecute);
    }

    private Department _department = new Department();
    public Department Department
    {
        get
        {
            return _department;
        }
        set
        {
            if (_department == value)
            {
                return;
            }
            _department = value;
            RaisePropertyChanged("Department");
        }
    }

    private Boolean CanExecute()
    {
        return true;
    }
    private void CreateDepartment()
    {
        bool success = departmentService.SaveDepartment(_department);
    }
}

DepartmentCode和DepartmentFullName绑定到UI，如下所示。

 <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <TextBlock Text="Department Code" Grid.Row="0"/>
        <TextBox Grid.Row="0" Text="{Binding Department.DepartmentCode, Mode=TwoWay}"  Margin="150,0,0,0"/>

        <TextBlock Text="Department Name" Grid.Row="1"/>
        <TextBox Grid.Row="1" Text="{Binding Department.DepartmentFullName, Mode=TwoWay}" ToolTip="Hi" Margin="150,0,0,0"/>

        <Button Grid.Row="2" Content="Save" Width="50" Command="{Binding CreateDepartmentCommand}"/>
    </Grid>

在保存Department之前，我需要验证DepartmentCode和DepartmentFullName是否包含一些文本。

我的验证逻辑应该放在哪里？ 在ViewModel本身？ 如果是这样，我如何将我的验证逻辑解耦，以便它也可以进行单元测试？

Answer 1

我发现最简单的方法是使用a

System.Windows.Controls.ValidationRule

它只需要3个直接的步骤。

首先，您创建一个ValidationRule。 这是一个完全独立的类，它存在于Model和ViewModel之外，并定义了如何验证Text数据。 在这种情况下，一个简单的String.IsNullOrWhiteSpace检查。

public class DepartmentValidationRule : System.Windows.Controls.ValidationRule
{
    public override System.Windows.Controls.ValidationResult Validate(object value, CultureInfo ultureInfo)
    {
        if (String.IsNullOrWhiteSpace(value as string))
        {
            return new System.Windows.Controls.ValidationResult(false, "The value is not a valid");
        }
        else
        {
            return new System.Windows.Controls.ValidationResult(true, null);
        }
    }
}

接下来，指定TextBoxes应使用新类的实例，通过指定Text绑定的ValidationRules属性对输入的Text执行验证。 如果验证失败，您将获得TextBox边框变红的额外奖励。

    <TextBlock Text="Department Code" Grid.Row="0"/>
    <TextBox Name="DepartmentCodeTextBox"  Grid.Row="0" Margin="150,0,0,0">
        <TextBox.Text>
            <Binding Path="Department.DepartmentCode" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged">
                <Binding.ValidationRules>
                    <local:DepartmentValidationRule/>
                </Binding.ValidationRules>
            </Binding>
        </TextBox.Text>
    </TextBox>
    <TextBlock Text="Department Name" Grid.Row="1"/>
    <TextBox Name="DepartmentNameTextBox" Grid.Row="1" ToolTip="Hi" Margin="150,0,0,0">
        <TextBox.Text>
            <Binding Path="Department.DepartmentFullName" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged">
                <Binding.ValidationRules>
                    <local:DepartmentValidationRule/>
                </Binding.ValidationRules>
            </Binding>
        </TextBox.Text>
    </TextBox>

最后，如果TextBox未通过验证，请创建一个样式以禁用“保存”按钮。 我们通过绑定到我们将验证规则绑定到的文本框的Validation.HasError属性来完成此操作。 我们将此样式命名为DisableOnValidationError，以使事情变得明显。

    <Grid.Resources>
        <Style x:Key="DisableOnValidationError" TargetType="Button">
            <Style.Triggers>
                <DataTrigger Binding="{Binding Path=(Validation.HasError), ElementName=DepartmentCodeTextBox}" Value="True" >
                    <Setter Property="IsEnabled" Value="False"/>
                </DataTrigger>
                <DataTrigger Binding="{Binding Path=(Validation.HasError), ElementName=DepartmentNameTextBox}" Value="True" >
                    <Setter Property="IsEnabled" Value="False"/>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Grid.Resources>

最后我们在Save按钮上设置DisableOnValidationError样式

    <Button Grid.Row="2" Content="Save" Width="50" Command="{Binding CreateDepartmentCommand}"
            Style="{StaticResource DisableOnValidationError}"/>

现在，如果您的任何一个TextBox未通过验证，TextBox将突出显示，并且将禁用“保存”按钮。

DepartmentValidationRule与业务逻辑完全分离，可重用且可测试。

Answer 2

创建一个DepartmentValidator类，它将很容易进行单元测试。 此外，此类还允许您消除服务器端和UI方案中的重复验证。

public class DepartmentValidator
{
    private class PropertyNames
    {
        public const string DepartmentFullName = "DepartmentFullName";
        public const string DepartmentCode = "DepartmentCode";
    }

    public IList<ValidationError> Validate(Department department)
    {
        var errors = new List<ValidationError>();

        if(string.IsNullOrWhiteSpace(department.DepartmentCode))
        {
            errors.Add(new ValidationError { ErrorDescription = "Department code must be specified.", Property = PropertyNames.DepartmentCode});
        }

        if(string.IsNullOrWhiteSpace(department.DepartmentFullName))
        {
            errors.Add(new ValidationError { ErrorDescription = "Department name must be specified.", Property = PropertyNames.DepartmentFullName});
        }

        if (errors.Count > 0)
        {
            return errors;
        }

        return null;
    }
}

创建一个包装Department模型并实现IDataErrorInfo的DepartmentViewModel，这样您就可以使用标准验证模板进行更精细的控制并显示验证错误。

public class DepartmentViewModel : IDataErrorInfo, INotifyPropertyChanged
{
    private Department _model;

    public DepartmentViewModel(Department model)
    {
        _model = model;
        Validator = new DepartmentValidator();
    }

    public DepartmentValidator Validator { get; set; }

    public string DepartmentFullName
    {
        get
        {
            return _model.DepartmentFullName;
        }
        set
        {
            if(_model.DepartmentFullName != value)
            {
                _model.DepartmentFullName = value;
                this.OnPropertyChanged("DepartmentFullName");
            }
        }
    }

    public string DepartmentCode
    {
        get
        {
            return _model.DepartmentCode;
        }
        set
        {
            if(_model.DepartmentCode != value)
            {
                _model.DepartmentCode = value;
                this.OnPropertyChanged("DepartmentCode");
            }
        }
    }

    public int DepartmentId
    {
        get
        {
            return _model.DepartmentId;
        }
    }

    public string this[string columnName]
    {
        get
        {
            var errors = Validator.Validate(_model) ?? new List<ValidationError>();
            if (errors.Any(p => p.Property == columnName))
            {
                return string.Join(Environment.NewLine, errors.Where(p => p.Property == columnName).Select(p => p.ErrorDescription));
            }
            return null;
        }
    }

    public string Error
    {
        get
        {
            var errors = Validator.Validate(_model) ?? new List<ValidationError>();
            return string.Join(Environment.NewLine, errors);
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = this.PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

公开DepartmentViewModel而不是Department Model，并将PropertyChanged事件连接到CreateDepartmentCommand，以便在部门验证失败时自动禁用Save按钮，以便显示验证错误。 公开ValidationErrors属性。

public CreateDepartmentViewModel(IDepartmentService DepartmentService)
{
    departmentService = DepartmentService;        
    _department = new DepartmentViewModel(new Department());
    this.CreateDepartmentCommand = new RelayCommand(CreateDepartment, CanExecute);

    _department.PropertyChanged += (s,a) => 
    {
       ValidationErrors = Department.Errors;
       RaisePropertyChanged("ValidationErrors");
       this.CreateDepartmentCommand.RaiseCanExecuteChanged();
    }  
}

public DepartmentViewModel Department
{
    get
    {
        return _department;
    }
    set
    {
        if (_department == value)
        {
            return;
        }
        _department = value;
        RaisePropertyChanged("Department");
    }
}

public string ValidationErrors {get; set;}

private Boolean CanExecute()
{
    return string.IsNullOrEmpty(ValidationErrors);
}

在保存部门之前，您可能希望再次进行验证。

private void CreateDepartment()
{
    if(Department.Error!=null)
    {
       ValidationErrors = Department.Error;
       RaisePropertyChanged("validationErrors");
       return;
    }

    bool success = departmentService.SaveDepartment(_department);
}

Answer 3

如何使用ValidationRules类，这将使您的模型与使用验证代码进行poppluting分离。

这对于单个控件非常有用 ，但您也可以将此逻辑委托给一些自定义验证类， MvvmValidator框架将对您有所帮助。 此框架允许您以规则的形式编写复杂的验证逻辑，这些规则可以在ViewModel级别配置，并可以在提交按钮上触发。 它是一种很好的解耦方式，可以在不填充domian对象的情况下应用验证。

Answer 4

在视图模型中添加新方法（Is Valid）和修改CanExecte方法，您可以通过测试CanExecute方法轻松测试：

public class CreateDepartmentViewModel : ViewModelBase
{
private IDepartmentService departmentService;
public RelayCommand CreateDepartmentCommand { get; private set; }

public CreateDepartmentViewModel(IDepartmentService DepartmentService)
{
    departmentService = DepartmentService;
    this.CreateDepartmentCommand = new RelayCommand(CreateDepartment, CanExecute);
}

private Department _department = new Department();
public Department Department
{
    get
    {
        return _department;
    }
    set
    {
        if (_department == value)
        {
            return;
        }
        _department = value;
        RaisePropertyChanged("Department");
    }
}
private bool IsValid()
{
 return !string.IsNullOrEmpty(this.Department.DepartmentCode) &&  !string.IsNullOrEmpty(this.Department.DepartmentFullName);
}

private Boolean CanExecute()
{
    return this.IsValid();
}
private void CreateDepartment()
{
    bool success = departmentService.SaveDepartment(_department);
}
}

Answer 5

您可以使您的Model类实现IDataErrorInfo接口。

如果您不想污染模型，可以创建一个继承自它的新类，并在那里进行验证

public class ValidDepartment : Department, IDataErrorInfo
{
    #region IDataErrorInfo Members

    public string Error
    {
        get { return null; }
    }

    public string this[string name]
    {
        get 
        {
            if (name == "DepartmentCode")
            {
                if (string.IsNullOrEmpty(DepartmentCode)
                    return "DepartmentCode can not be empty";
            }

            if (name == "DepartmentFullName")
            {
                if (string.IsNullOrEmpty(DepartmentFullName)
                    return "DepartmentFullName can not be empty";
            }

            return null;
        }
    }

    #endregion
}

在ViewModel用ValidDepartment替换Department

private ValidDepartment _department = new ValidDepartment ();
public ValidDepartment Department
{
    get
    {
        return _department;
    }
    set
    {
        if (_department == value)
        {
            return;
        }
        _department = value;
        RaisePropertyChanged("Department");
    }
}

在您的View集中， ValidatesOnDataErrors=True到绑定控件

<TextBox Grid.Row="1" ToolTip="Hi" Margin="150,0,0,0">
   <TextBox.Text>
       <Binding Path="Department.DepartmentFullName"
                Mode="TwoWay"
                ValidatesOnDataErrors="True">
        </Binding>
    </TextBox.Text>
</TextBox>

设置TextBox Style和Validation.ErrorTemplate以确定验证在UI中的显示方式，例如，通过Tooltip：

<Style x:Key="textBoxInError" TargetType="{x:Type TextBox}">
  <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>

您可以了解更多有关验证在WPF 这里 ，并在这里

希望这可以帮助

Answer 6

我也觉得这很烦人，因为它会将您的业务逻辑驱动到ViewModel迫使您接受并将其留在那里或在Service Layer或Data Model复制它。 如果你不介意失去使用注释等的一些优点。 这是我使用过的最常推荐的方法 - 从服务层向ValidationDictionary添加错误。

您还可以将这些与在服务层中按上述方式处理的业务逻辑以及在ViewModel注释的仅UI相关验证混合使用。

*请注意，我从MVC的角度回答这个问题，但我认为这仍然是相关的。

Answer 7

我在所有项目中使用流畅的验证，不仅可以解耦，还可以轻松地对我的验证规则进行单元测试。 http://fluentvalidation.codeplex.com/ 。

它还有一个nuget包http://www.nuget.org/packages/FluentValidation/