DataBinding to Properties of a Collection

[charlie]

I have been messing around with data binding on Windows Forms, and I'm
having a problem with the Property of a Collection (myCollection.Count)
getting out of synch with label it's bound to.

(My real problem is binding to a Property of a Collection, and not just
the simpler case of the .Count property)

I'm using the following syntax to bind the object to the label.

1.) label1.DataBindings.Add("Text", myCollection.Count, "");

If I then add a new item to my collection through code, the label for
the Count does not get updated. I initially had this problem with a
simple object that has a TotalPrice property that is a calculated field
(based on Quantity * UnitPrice) , but I was able to add an event that
triggered the GUI to get the new calculated value.

public event EventHandler TotalPriceChanged;

public void OnTotalPriceChanged()
{
if (TotalPriceChanged!= null)
TotalPriceChanged(this, new EventArgs());
}

public int TotalPrice
{
get
{
return _totalPrice;
}
set
{
_totalPrice = value;
OnTotalPriceChanged();
}
}

In this case I had to use the following syntax to bind the TotalPrice,
where I specify the 3rd parameter as the property name, instead of
including it in the 2nd parameter as I did above.

2.) label1.DataBindings.Add("Text", myObj, "TotalPrice");

However, if I'm binding to a Property of a Collection using the Syntax
from #2, I get an System.ArgumentException 'Can not bind to property or
column Count on datasource.' What I think is going on here is that it's
trying to bind to the Currently Selected Item in the Collection, which
does not have a Count property.

Am I just missing something, or do Properties of Collections not have
any way to bind and keep their data synchronized between the Collection
object and the GUI?

TIA,
Charlie

 

[Alexander Shirshov]

Charlie,

You are correct, when you do this:

label1.DataBindings.Add("Text", myCollection, "Count");

the binding code is trying to find Count property on element of the
collection.

What you could do is create a simple wrapper class for your collection with
Count property and CountChanged event and bound to it.

Alexander

 

[Alexander Shirshov]

Charlie,

You are correct, when you do this:

label1.DataBindings.Add("Text", myCollection, "Count");

the binding code is trying to find Count property on element of the
collection.

What you could do is create a simple wrapper class for your collection with
Count property and CountChanged event and bind to it.

Alexander