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Difficult! Bound user control property haschanges in dataset when no changes are made.

Posted on 2004-09-16
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Last Modified: 2008-03-10
When databinding to the text property of a textbox the getchanges property of the dataset will only return values if the textbox is changed.
If I bind to a property of any usercontrol, dataset.haschanges will always be true.
I want my property to work like the text property.
Any code replies can be in C#.NET or VB.NET.

Here is the relevent code:

'User Control Property Declaration:
_________________________________________________________
Public Class UserControl1
    Inherits System.Windows.Forms.UserControl
    Private _BindMe As String

    <Bindable(True)> _
    Public Property BindMe() As String
        Get
            Dim myBinding As Windows.Forms.Binding
            Return _BindMe
        End Get
        Set(ByVal Value As String)
            _BindMe = Value
        End Set
    End Property

End Class
__________________________________________________________
'FORM Code

'DataBinding:
Me.UserControl11.DataBindings.Add(New System.Windows.Forms.Binding("BindMe", Me.DataSet11, "Customers.CompanyName"))

'Save:
Me.BindingContext.Item(Me.DataSet11, "Customers").EndCurrentEdit()
MsgBox("Has Changes: " & Me.DataSet11.HasChanges.ToString)
Me.SqlDataAdapter1.Update(Me.DataSet11)
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Question by:RobertRFreeman
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  • 4
8 Comments
 
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Expert Comment

by:jackiechen858
ID: 12086352
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Accepted Solution

by:
jackiechen858 earned 2000 total points
ID: 12086643
           public string BindMe
            {
                  get
                  {
                        return _BindMe;
                  }
                  set
                  {
                        if ( _BindMe != value)
                        {
                              _BindMe = value;
                              RaiseChangeEvent();
                        }
                        else
                        {
                        }
                  }
            }
            public event EventHandler BindMeChanged ;
            private void RaiseChangeEvent ()
            {
                  BindMeChanged(this,null);
            }

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Author Comment

by:RobertRFreeman
ID: 12086997
Thank you both very much.  Here is the code in VB.  Now I can make properties that handle simple binding correctly.  WooHoo!
I found more documentation under Property Usage Guidelines in MSDN by searching for "property-changed events" or "properties, usage guidelines" in the index.

    Public Event BindMeChanged As PropertyChangedEventHandler

    <Bindable(True)> _
    Public Property BindMe() As String
        Get
            Dim myBinding As Windows.Forms.Binding
            Return _BindMe
        End Get
        Set(ByVal Value As String)
            If _BindMe <> Value Then
                _BindMe = Value
                RaiseEvent BindMeChanged(Me, New PropertyChangedEventArgs("BindMe"))
            End If
        End Set
    End Property
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Expert Comment

by:jackiechen858
ID: 12087885
you are welcome.
0
 
LVL 16

Author Comment

by:RobertRFreeman
ID: 12088652
My last post has a bug, here is the correct code.

    Private _BindMe As String
    Public Event BindMeChanged As EventHandler

    <Bindable(True)> _
    Public Property BindMe() As String
        Get
            Dim myBinding As Windows.Forms.Binding
            Return _BindMe
        End Get
        Set(ByVal Value As String)
            If _BindMe <> Value Then
                _BindMe = Value
                RaiseBindMeChanged()
            End If
        End Set
    End Property

    Protected Sub RaiseBindMeChanged()
        RaiseEvent BindMeChanged(Me, New EventArgs)
    End Sub
0
 
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Expert Comment

by:jackiechen858
ID: 12088700
When I read your code, I really thought there is a PropertyChangedEventHandler :-)
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Author Comment

by:RobertRFreeman
ID: 12088741
There is. :)  It just doesn't work like I thought.  Let me know if you figure out what it does.
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Author Comment

by:RobertRFreeman
ID: 12221367
One other issue I found with using a usercontrol as a combobox is that the text is highlighted on initialization.  I think I found a workaround, but this solution causes an error in the design time environment.  When the control is on another form, the following VS.net error occurs: '-195465169' is not a valid value for 'start'.

Here is the workaround code in my databound combobox usercontrol:
    Protected Overrides Sub OnPaint(ByVal e As System.Windows.Forms.PaintEventArgs)
        MyBase.OnPaint(e)
        'Gets rid of the selection
        If Me.ComboBox1.SelectionLength > 0 Then
            Me.ComboBox1.SelectionLength = 0
        End If
    End Sub

I may post this as another question.
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