Validation and last value of textbox on MVVM

Question

I have such textbox declaration:

<TextBox x:Name="InputTextBox">
                <Binding Path="Input" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged">
                    <Binding.ValidationRules>
                        <MyValidationRule
                        ErrorMessage="Invalid" />
                    </Binding.ValidationRules>
                </Binding>
                <TextBox.InputBindings>
                    <KeyBinding Key="Enter" Command="{Binding Path=AddCommand}"/>
                </InputBindings> 
  </TextBox>

Such validationRule hierarchy:

public abstract class AbstractValidationRule : ValidationRule
{
    public string ErrorMessage { get; set; }

    protected abstract bool IsValid(string inputString)

    public override ValidationResult Validate(object value, CultureInfo cultureInfo)
    {
        string inputString = (value ?? string.Empty).ToString();

        if (!IsValid(inputString)) return new ValidationResult(false, ErrorMessage);
        return new ValidationResult(true, null);
    }
}

class MyValidationRule : AbstractStringValidationRule
{
    protected override bool IsValid(string inputString)
    {
        return !String.IsNotNullOrEmpty(inputString);
    }
}

Add command:

    public ICommand AddCommand
    {
        get
        {
            return m_AddCommand ??
                   (m_AddCommand = new DelegateCommand(Add));
        }
    }

private void Add()
    {
        InternalValue = Input;
        // input = Old invalid value
        OnPropertyChanged("Input")
    }

Input property:

  public string Input
    {
        get { return m_Input; }
        set
        {
            if (m_Input != value)
            {
                m_Input = value;
                OnPropertyChanged("Input");
            }
        }
    }

If I entered "valid" and then "invalid", When command was executed, property Input will be set in "valid" value state. I tried another way with UpdateSourceTrigger="Explicit" and using TextChanged event - was still same result.

Without ValidationRule - all works good.

PS I cannot change class from model layer.

Answer 1

嗨，设置UpdateSourceTrigger =“ PropertyChanged”。希望这会有所帮助。

Answer 2

if you want that your validation/viewmodel and your "ui" are in sync then you should use IDataErrorInfo. your Input property should hold "valid" AND "invalid" values.