Why does GetChanges return something (when bound to a property) even though there is no change to the datatable?
Bound GetChanges
always returns something when binding to a property UserControl
(even on a simple one)
I did UserControl
, for some reason unbeknownst to me, when I bound DataColumn
to a control property, it dataSet1.GetChanges()
always returned something, even the column associated with my control was not changed.
What's the possible reason for GetChanges
always returning something?
Here's a simple snippet to reproduce the bind / GetChanges issue:
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
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I managed to solve the problem today, the main thing is to make the BindingContext EndCurrentEdit aware if the value has actually changed. for this we have to implement System.ComponentModel.INotifypropertychanged in our control. i just saw the solution from here: http://msdn.microsoft.com/en-us/library/system.componentmodel.inotifypropertychanged.propertychanged.aspx
hope this can help other users implement their own controls that do not match the change status on GetChanges ()
public partial class Form1 : Form, System.ComponentModel.INotifyPropertyChanged
{
//----------- implements INotifyPropertyChanged -----------
// wish C# has this VB.NET 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);
}
}
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