C# MVVM模式下的数据验证方法

在C#中使用MVVM模式进行数据验证可以通过以下方法实现：

1. 使用INotifyDataErrorInfo接口：在ViewModel中实现INotifyDataErrorInfo接口，并在属性的setter中进行数据验证，然后通过ErrorsChanged事件通知View。

public class ViewModel : INotifyDataErrorInfo {     private string _username;     public string Username     {         get { return _username; }         set         {             if (string.IsNullOrEmpty(value))             {                 AddError("Username", "Username cannot be empty");             }             else             {                 RemoveError("Username");             }             _username = value;             OnPropertyChanged("Username");         }     }      private Dictionary<string, List<string>> _errors = new Dictionary<string, List<string>>();      public event EventHandler<DataErrorsChangedEventArgs> ErrorsChanged;      public IEnumerable GetErrors(string propertyName)     {         if (_errors.ContainsKey(propertyName))             return _errors[propertyName];         return null;     }      public bool HasErrors => _errors.Any();      private void AddError(string propertyName, string error)     {         if (!_errors.ContainsKey(propertyName))             _errors[propertyName] = new List<string>();         if (!_errors[propertyName].Contains(error))         {             _errors[propertyName].Add(error);             ErrorsChanged?.Invoke(this, new DataErrorsChangedEventArgs(propertyName));         }     }      private void RemoveError(string propertyName)     {         if (_errors.ContainsKey(propertyName))         {             _errors.Remove(propertyName);             ErrorsChanged?.Invoke(this, new DataErrorsChangedEventArgs(propertyName));         }     }      private void OnPropertyChanged(string propertyName)     {         PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));     } } 

2. 使用IDataErrorInfo接口：ViewModel类实现IDataErrorInfo接口，对属性进行数据验证，并在Error属性中返回错误信息。

public class ViewModel : IDataErrorInfo {     private string _username;     public string Username     {         get { return _username; }         set         {             if (string.IsNullOrEmpty(value))             {                 Error = "Username cannot be empty";             }             else             {                 Error = null;             }             _username = value;             OnPropertyChanged("Username");         }     }      public string Error { get; private set; }      public string this[string columnName]     {         get         {             switch (columnName)             {                 case "Username":                     if (string.IsNullOrEmpty(Username))                         return "Username cannot be empty";                     break;             }             return null;         }     }      private void OnPropertyChanged(string propertyName)     {         PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));     } } 

这样在View中绑定ViewModel的属性时，会实时进行数据验证，并显示错误信息。