爲什麼GetChanges會返回一些東西（綁定到屬性時），即使數據表中沒有更改？

Question

綁定GetChanges當綁定到UserControl的財產（甚至一個簡單的）

我已經做了UserControl，出於某種原因瞞着我總是返回的東西，當我綁定一個DataColumn到我的控件的屬性的dataSet1.GetChanges()總是返回一些東西，即使是綁定到我的控件的列也沒有改變。

GetChanges總是返回什麼可能的原因是什麼？

這裏有一個簡單的代碼片段重現綁定/ GetChanges問題：

---

using System; 

using System.Data; 

using System.Windows.Forms; 


namespace BindingBug 
{ 

    public partial class Form1 : Form 
    { 

     DataSet _ds = new DataSet(); 

     void GetData() 
     {   
      var t = new DataTable 
      { 
       TableName = "beatles", 
       Columns = 
       { 
        {"lastname", typeof(string)}, 
        {"firstname", typeof(string)}, 
        {"middlename", typeof(string)} 
       } 
      }; 


      t.Rows.Add("Lennon", "John", "Winston"); 
      t.Rows.Add("McCartney", "James", "Paul"); 

      _ds.Tables.Add(t);    
     } 

     public string Hey { set; get; } 

     public Form1() 
     { 
      InitializeComponent(); 

      var tLastname = new TextBox { Top = 100 }; 
      var tFirstname = new TextBox { Top = 130 }; 

      this.Controls.Add(tLastname); 
      this.Controls.Add(tFirstname); 

      GetData(); 


      tLastname.DataBindings.Add("Text", _ds.Tables["beatles"], "lastname"); 
      tFirstname.DataBindings.Add("Text", _ds.Tables["beatles"], "firstname"); 

      // if the following line is commented 2nd:Has Changes == false 
      this.DataBindings.Add("Hey", _ds.Tables["beatles"], "middlename"); 


      _ds.AcceptChanges(); 


      MessageBox.Show("1st:Has Changes = " + _ds.HasChanges().ToString()); 

      var bDetectChanges = new Button { Top = 160, Text = "Detect Changes" }; 
      bDetectChanges.Click += 
       delegate 
       { 
        this.BindingContext[_ds.Tables["beatles"]].EndCurrentEdit(); 
        MessageBox.Show("2nd:Has Changes = " + (_ds.GetChanges() != null).ToString()); 
       }; 

      this.Controls.Add(bDetectChanges); 

     }  
    } 
} //namespace BindingBug 

Answer 1

我今天總算得以解決這個問題，關鍵是要做出的BindingContext的EndCurrentEdit意識到如果該值真已更改。爲此，我們必須在我們的控件上實現System.ComponentModel.INotifypropertychanged。我剛纔看到從這裏的解決方案：​​

希望這可以幫助其他人實現自己的控制，其標誌錯誤變化對GetChanges狀態（）

public partial class Form1 : Form, System.ComponentModel.INotifyPropertyChanged 
{ 
    //----------- implements INotifyPropertyChanged ----------- 


    // wish C# has this VB.NET's syntactic sugar 
    public event System.ComponentModel.PropertyChangedEventHandler PropertyChanged; // implements INotifyPropertyChanged.PropertyChanged 

    //----------- start of Form1 ---------- 


    DataSet _ds = new DataSet(); 



    void NotifyPropertyChanged(string propertyName) 
    { 
     if (PropertyChanged != null) 
      PropertyChanged(this, new System.ComponentModel.PropertyChangedEventArgs(propertyName)); 
    } 



    void GetData() 
    { 

     var t = new DataTable 
     { 
      TableName = "beatles", 
      Columns = 
      { 
       {"lastname", typeof(string)}, 
       {"firstname", typeof(string)}, 
       {"middlename", typeof(string)} 
      } 
     }; 


     t.Rows.Add("Lennon", "John", "Winston"); 
     t.Rows.Add("McCartney", "James", "Paul"); 

     t.Columns["middlename"].DefaultValue = ""; 

     _ds.Tables.Add(t);    
    } 



    string _hey = ""; 
    public string Hey 
    { 
     set 
     { 
      if (value != _hey) 
      { 
       _hey = value; 
       NotifyPropertyChanged("Hey"); 
      } 
     } 
     get 
     {     

      return _hey; 
     } 
    } 



    public Form1() 
    { 
     InitializeComponent(); 



     var tLastname = new TextBox { Top = 100 }; 
     var tFirstname = new TextBox { Top = 130 }; 

     this.Controls.Add(tLastname); 
     this.Controls.Add(tFirstname); 

     GetData(); 



     tLastname.DataBindings.Add("Text", _ds.Tables["beatles"], "lastname"); 
     tFirstname.DataBindings.Add("Text", _ds.Tables["beatles"], "firstname"); 

     this.DataBindings.Add("Hey", _ds.Tables["beatles"], "middlename"); 


     _ds.AcceptChanges(); 




     MessageBox.Show("1st:Has Changes = " + _ds.HasChanges().ToString()); 

     var bDetectChanges = new Button { Top = 160, Text = "Detect Changes" }; 
     bDetectChanges.Click += 
      delegate 
      { 
       this.BindingContext[_ds.Tables["beatles"]].EndCurrentEdit(); 
       MessageBox.Show("2nd:Has Changes = " + (_ds.GetChanges() != null).ToString()); 

      }; 

     this.Controls.Add(bDetectChanges); 

    } 

}