如何從ViewModel中分離ViewModel屬性驗證？

Question

我正在使用MVVMLight。 這是我的Department模型/ POCO課程。 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; }
    }

這是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綁定到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，我需要驗證DepartmentCode和DepartmentFullName是否包含一些文本。

我的驗證邏輯應該放在哪里？ 在ViewModel本身？ 如果是這樣，我如何將我的驗證邏輯解耦，以便它也可以進行單元測試？

Answer 1

我發現最簡單的方法是使用a

System.Windows.Controls.ValidationRule

它只需要3個直接的步驟。

首先，您創建一個ValidationRule。 這是一個完全獨立的類，它存在於Model和ViewModel之外，並定義了如何驗證Text數據。 在這種情況下，一個簡單的String.IsNullOrWhiteSpace檢查。

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);
        }
    }
}

接下來，指定TextBoxes應使用新類的實例，通過指定Text綁定的ValidationRules屬性對輸入的Text執行驗證。 如果驗證失敗，您將獲得TextBox邊框變紅的額外獎勵。

    <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未通過驗證，請創建一個樣式以禁用“保存”按鈕。 我們通過綁定到我們將驗證規則綁定到的文本框的Validation.HasError屬性來完成此操作。 我們將此樣式命名為DisableOnValidationError，以使事情變得明顯。

    <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>

最后我們在Save按鈕上設置DisableOnValidationError樣式

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

現在，如果您的任何一個TextBox未通過驗證，TextBox將突出顯示，並且將禁用“保存”按鈕。

DepartmentValidationRule與業務邏輯完全分離，可重用且可測試。

Answer 2

創建一個DepartmentValidator類，它將很容易進行單元測試。 此外，此類還允許您消除服務器端和UI方案中的重復驗證。

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;
    }
}

創建一個包裝Department模型並實現IDataErrorInfo的DepartmentViewModel，這樣您就可以使用標准驗證模板進行更精細的控制並顯示驗證錯誤。

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));
        }
    }
}

公開DepartmentViewModel而不是Department Model，並將PropertyChanged事件連接到CreateDepartmentCommand，以便在部門驗證失敗時自動禁用Save按鈕，以便顯示驗證錯誤。 公開ValidationErrors屬性。

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);
}

在保存部門之前，您可能希望再次進行驗證。

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類，這將使您的模型與使用驗證代碼進行poppluting分離。

這對於單個控件非常有用 ，但您也可以將此邏輯委托給一些自定義驗證類， MvvmValidator框架將對您有所幫助。 此框架允許您以規則的形式編寫復雜的驗證邏輯，這些規則可以在ViewModel級別配置，並可以在提交按鈕上觸發。 它是一種很好的解耦方式，可以在不填充domian對象的情況下應用驗證。

Answer 4

在視圖模型中添加新方法（Is Valid）和修改CanExecte方法，您可以通過測試CanExecute方法輕松測試：

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類實現IDataErrorInfo接口。

如果您不想污染模型，可以創建一個繼承自它的新類，並在那里進行驗證

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替換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到綁定控件

<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>

設置TextBox Style和Validation.ErrorTemplate以確定驗證在UI中的顯示方式，例如，通過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>

您可以了解更多有關驗證在WPF 這里 ，並在這里

希望這可以幫助

Answer 6

我也覺得這很煩人，因為它會將您的業務邏輯驅動到ViewModel迫使您接受並將其留在那里或在Service Layer或Data Model復制它。 如果你不介意失去使用注釋等的一些優點。 這是我使用過的最常推薦的方法 - 從服務層向ValidationDictionary添加錯誤。

您還可以將這些與在服務層中按上述方式處理的業務邏輯以及在ViewModel注釋的僅UI相關驗證混合使用。

*請注意，我從MVC的角度回答這個問題，但我認為這仍然是相關的。

Answer 7

我在所有項目中使用流暢的驗證，不僅可以解耦，還可以輕松地對我的驗證規則進行單元測試。 http://fluentvalidation.codeplex.com/ 。

它還有一個nuget包http://www.nuget.org/packages/FluentValidation/