Question

我有一个Customer类，我想在用户更改Customer.CityInfo属性的值时收到通知。

public class City
{
    public long Id {get;set;}
    public string Code {get;set;}
}

public class Customer
{

    private City cityInfo;
    private string name;

    public long Id { get; set; }
    public bool IsCityModified { get; set;}
    public bool IsCustomerNameModified { get; set; }

    public string Name 
    { 
        get{ return name;} 
        set
        {
           if(name!=value)
           {
              IsCustomerNameModified=true; }name=value;
           } 
        }
     }


    public City CityInfo 
    {
    get
        {
           if(cityInfo==null)
           {
              cityInfo=new City();
           }
           return cityInfo;
         }

      set{
          if(this.cityInfo!=value)
          {
             IsCityModified =true;
          }
          this.cityInfo=value;
       }   
  }
}

public ActionResult Save()
{
    Customer customer=this.currentCustomerSession;
    if(TryUpdateModel<Customer>(customer)){
       UpdateModel<Customer>(customer)
    }
    if(customer.IsCustomerNameModified ){
        //I am able to detect whether the customerName value has been changed in the frontend.
    }
    if(customer.IsCityModified){
        //I am not able to detect whether the city value has been changed in the frontend.
    }
}

如果Customer Name因其值类型而更改，我可以将标志（IsCustomerNameModified）设置为true。但无法检测参考类型中所做的更改。

有人可以帮忙吗？

Answer 1

此类问题通常通过变更通知系统处理。请参阅此文章：How to: Implement Property Change Notification

段：

  public string PersonName
  {
      get { return name; }
      set
      {
          name = value;
          // Call OnPropertyChanged whenever the property is updated
          OnPropertyChanged("PersonName");
      }
  }

  // Create the OnPropertyChanged method to raise the event 
  protected void OnPropertyChanged(string name)
  {
      PropertyChangedEventHandler handler = PropertyChanged;
      if (handler != null)
      {
          handler(this, new PropertyChangedEventArgs(name));
      }
  }

使用此模式可以帮助您避免设置标记或其他此类阴谋。

Answer 2

现在我正确地理解了这个问题，我建议你做以下事情：

在public bool Changed { get; private set; }对象中添加City属性。

然后在对象的每个属性中，检查值是否已更改，如果已更改，则将Changed标志置为true：

public int Id
{
   { get { return this.id } }
   {
      set
      {
         if (this.id != value) Changed = true;
         this.id = value;
      }
   }
}

它类似于实现IPropertyChanged接口，但是这样您确定只能检查对象是否被修改过一次。

似乎你的对象的引用没有改变，所以你只需要检查它的Changed属性（如果对象的引用真的改变了，我的先例答案就会起作用）

Answer 3

保罗是正确的，您需要实施INotifyProperty更改。这是一个简单的例子。这很简单。

  public class BaseViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        private int _number;

        public BaseViewModel()
        {
            PropertyChanged += (o, p) =>
                                   {
                                       //this is the place you would do what you wanted to do
                                       //when the property has changed.
                                   };
        }

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

        public int Number
        {
            get { return _number; }
            set
            {
                _number = value;
                OnPropertyChanged("Number");
            }
        }
    }

Answer 4

我同意Paul的回答，但您甚至可能需要覆盖City类中的Equals（）和GetHashCode（）函数。被覆盖的函数可以检查代码和ID是否已更改。

public override bool Equals( object obj )
{
    City other = obj as City;

    if ( ( other != null ) && ( other.Id == this.Id ) && ( other.Code == this.Code ) )
    {
        return ( true );
    }

    return ( false );
}

public override int GetHashCode( )
{
    return ( this.Id ^ this.Code.GetHashCode() ) ;
}

Answer 5

您可以使用INotifyPropertyChanged，但我猜您没有将对象绑定到某个UI元素。在这种情况下，如果仅需要知道CityInfo属性是否更改，则最简单解决方案是提出自定义事件。

public class Customer
{

    private City cityInfo;
    private string name;

    public long Id { get; set; }
    public bool IsCityModified { get; set;}
    public event Action<City> OnCityInfoChanged;
    public bool IsCustomerNameModified { get; set; }

    public string Name 
    { 
        get{ return name;} 
        set
        {
           if(name!=value)
           {
              IsCustomerNameModified=true; }name=value;
           } 
        }
     }


    public City CityInfo 
    {
    get
        {
           if(cityInfo==null)
           {
              cityInfo=new City();
           }
           return cityInfo;
         }

      set{
          if(this.cityInfo ==value)
                  return;
             IsCityModified =true;
             this.cityInfo=value;
             if(OnCityInfoChanged != null)
                OnCityInfoChanged(value);
       }   
  }
}

和

public ActionResult Save()
{
    Customer customer=this.currentCustomerSession;
customer.OnCityInfoChanged += new Action<CityInfo>( (cityInfo) => {//Do Something with New CityInfo});
    if(TryUpdateModel<Customer>(customer)){
       UpdateModel<Customer>(customer)
    }
    if(customer.IsCustomerNameModified ){
        //I am able to detect whether the customerName value has been changed in the frontend.
    }
    if(customer.IsCityModified){
        //I am not able to detect whether the city value has been changed in the frontend.
    }
}

如何检测c＃中的属性值（ReferenceType属性）是否发生了变化？

5 个答案: