如何檢測屬性值（引用類型屬性）在c＃中更改？

Question

我有一個Customer類，我希望在用戶更改Customer.CityInfo屬性的值時收到通知。

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. 
    } 
} 

我可以，如果客戶名稱，因爲它的值類型更改標誌（IsCustomerNameModified）設置爲true。但無法檢測參考類型中所做的更改。

任何人都可以幫忙嗎？

Answer 1

這類問題通常是通過更改通知系統處理的。看到這篇文章：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)); 
     } 
    } 

使用此模式將幫助您避免需要設置標誌或其他類似的陰謀。現在

Answer 2

，我理解正確的問題，我建議做到以下幾點：

在City對象添加public bool Changed { get; private set; }屬性。

然後在你的對象的每個屬性，檢查值發生了變化，如果有，然後把Changed標誌設置爲true：

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

它類似於實施IPropertyChanged接口，但是這你確信你只能檢查對象是否被修改過一次。

看來你的對象的引用並沒有改變，所以你只需要檢查它的Changed屬性（如果該對象的引用真的變了，我的先例答案會工作）

Answer 3

保羅是正確的，你需要實施INotifyProperty更改。這是一個簡單的例子。這很簡單。

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，但您甚至可能需要重寫City類中的Equals（）和GetHashCode（）函數。重寫的函數可以檢查代碼和ID是否已經改變。

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

你可以使用INotifyPropertyChanged，但我想你沒有將對象綁定到某個UI元素。 在這種情況下，如果只需要知道CityInfo屬性是否更改，最簡單的解決方案就是引發自定義事件。

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); 
     } 
    } 
} 

而且

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. 
    } 
}