Binding a textbox to a nullable datatype.

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markk@nait.ca - 22 Oct 2006 18:41 GMT

I am wondering if there is a better solution, than the one I came up
with...

I am binding a textbox to a nullable float (float?) and want the
ability for the user to leave the textbox blank, indicating that it is
null. If you do not alter the behavior of the textbox, the user, when
attempting to leave the textbox would not be allowed because the empty
string is not a valid value of the binding property (float?).

In order to get around this I overloaded the OnValidating eventhandler.

protected override void OnValidating(CancelEventArgs e)
{
if (this.Text == "" && this.BindingContext != null)
{
e.Cancel = false;
base.Text = null;

object o = ((this.DataBindings[0].DataSource as
BindingSource)).DataSource;
PropertyInfo pi =
o.GetType().GetProperty(this.DataBindings[0].BindingMemberInfo.BindingMember);
pi.SetValue(o, null, null);

}
else
base.OnValidating(e);
}

Is there a better way?

Reply to this Message

Bart Mermuys - 22 Oct 2006 20:49 GMT

Hi,

>I am wondering if there is a better solution, than the one I came up
> with...
[quoted text clipped - 26 lines]
>
> Is there a better way?

There are other ways, you decide what you like most:

1) Since it looks like you are inheriting the TextBox, you could override
Text instead, eg. :

public override string Text
{
get
{
return ((base.Text=="") && !DesignMode)? null : base.Text;
}
set
{
base.Text = value;
}
}

2) Instead of inheriting from TextBox, you could attach an eventhandler to
the DataBinding Parse event, eg. :

// if you have setup the bindings using the designer then attach the
eventhandler
// after InitializeComponent
textBox1.DataBindings.Add("Text", yourBindingSource, "yourField");
textBox1.DataBindings["Text"].Parse += new ConvertEventHandler(
StringToFloatHandler );

private void StringToFloatHandler (object sender, ConvertEventArgs e)
{
string str = e.Value as string;
e.Value = (str=="")? (float?)null : float.Parse(str);
}

HTH,
Greetings

Reply to this Message

AnikSol - 26 Oct 2006 14:45 GMT

Hi Bart,

Any chance that you could post your suggestions 1 and 2 in VB?

thanks n regards

> Hi,
>
[quoted text clipped - 64 lines]
> HTH,
> Greetings

Reply to this Message

Bart Mermuys - 26 Oct 2006 21:24 GMT

Hi,

> Hi Bart,
>
> Any chance that you could post your suggestions 1 and 2 in VB?

I'm not very familar with nullable types in VB, but it here it goes:

1)
Public Overrides Property Text() As String
Get
Return IIf((MyBase.Text = "") And Not DesignMode, Nothing, MyBase.Text)
End Get
Set(ByVal value As String)
MyBase.Text = value
End Set
End Property

2)

AddHandler TextBox1.DataBindings("Text").Parse, AddressOf
StringToFloatHandler

Private Sub StringToFloatHandler( ByVal sender As Object, ByVal e As
ConvertEventArgs )

Dim str As String = CStr( e.Value )
e.Value = IIf(str = "", Nothing, float.Parse(str) )

End Sub

HTH,
Greetings

> thanks n regards
>
[quoted text clipped - 66 lines]
>> HTH,
>> Greetings

Reply to this Message

AnikSol - 27 Oct 2006 03:04 GMT

Bart

Thanks.

> Hi,
>
[quoted text clipped - 100 lines]
>>> HTH,
>>> Greetings

Reply to this Message

Binding a textbox to a nullable datatype.

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