WPF-ValidationRule沒有被調用

Question

我得到了TextBlock的Xaml：

<TextBlock VerticalAlignment="Center">
       <TextBlock.Text>
             <Binding Path="FilesPath" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged">
                  <Binding.ValidationRules>
                        <viewModel:ExtensionRule></viewModel:ExtensionRule>
                   </Binding.ValidationRules>
              </Binding>
         </TextBlock.Text>
 </TextBlock>

在ViewModel中：

    private string _filesPath;
    public string FilesPath
    {
        set 
        { 
            _filesPath = value;
            OnPropertyChange("FilesPath");
        }
        get { return _filesPath; }
    }

    private void OnPropertyChange(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

驗證規則是這樣的：

public class ExtensionRule : ValidationRule
{
    public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
    {
        string filePath = String.Empty;
        filePath = (string)value;
        if (String.IsNullOrEmpty(filePath))
        {
            return new ValidationResult(false, "Must give a path");
        }

        if (!File.Exists(filePath))
        {
            return new ValidationResult(false, "File not found");
        }
        string ext = Path.GetExtension(filePath);
        if (!ext.ToLower().Contains("txt"))
        {
            return new ValidationResult(false, "given file does not end with the \".txt\" file extenstion");
        }
        return new ValidationResult(true, null);
    }
}

並且另一個事件正在更新FilesPath屬性：（vm是viewModel var）

private void BrowseButton_Click(object sender, RoutedEventArgs e)
    {
        // Create OpenFileDialog 
        OpenFileDialog dlg = new OpenFileDialog();

        // Set filter for file extension and default file extension 
        dlg.DefaultExt = ".txt";
        dlg.Filter = "txt Files (*.txt)|*.txt";

        // Display OpenFileDialog by calling ShowDialog method 
        bool? result = dlg.ShowDialog();

        // Get the selected file name and display in a TextBox 
        if (result == true)
        {
            // Open document 
            string filename = dlg.FileName;
            vm.FilesPath = filename;
        }
    }

當我通過文件對話框選擇文件時，為什么不調用ValidationRule？

Answer 1

根據此MSDN Library文章 ，僅當將數據從綁定的目標屬性（在您的情況下為TextBlock.Text ）傳輸到源屬性（您的vm.FilesPath屬性）時，才會檢查驗證規則-例如，此處的目的是驗證用戶輸入，一個TextBox 。 為了將驗證反饋從源屬性傳遞給擁有目標屬性的控件（ TextBlock控件），您的視圖模型應實現IDataErrorInfo或INotifyDataErrorInfo 。