I'm having trouble with a situation that I know must be pretty common, so I'm hoping the solution is simple. I have an object that contains a List<> of objects. It also has some properties that reflect aggregate data on the objects in the List<> (actually a BindingList<> so I can bind to it). On my form, I have a DataGridView for the List, and some other fields for the aggregate data. I can't figure out how to trigger a refresh of the aggregate data when values in the DataGridView get changed.
I have tried raising a PropertyChanged event when the properties of the objects in the List are changed, but that doesn't seem to refresh the display of the aggregate data. If I access an aggregate property (eg, display it in a messagebox), the textbox on the main form is refreshed.
Here's some simplified code to illustrate what I'm trying to do:
namespace WindowsFormsApplication1 {
public class Person {
public int Age {
get;
set;
}
public String Name {
get;
set;
}
}
public class Roster : INotifyPropertyChanged {
public BindingList<Person> People {
get;
set;
}
public Roster () {
People = new BindingList<Person>();
}
private int totalage;
public int TotalAge {
get {
calcAges();
return totalage;
}
set {
totalage = value;
NotifyPropertyChanged("TotalAge");
}
}
private void calcAges () {
int total = 0;
foreach ( Person p in People ) {
total += p.Age;
}
TotalAge = total;
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged ( String info ) {
if ( PropertyChanged != null ) {
PropertyChanged(this, new PropertyChangedEventArgs(info));
}
}
#endregion
}
}
Best Answer
The
calcAges
method and theTotalAge
property look very suspicious.First,
TotalAge
should be read-only. If you allow it to be public and writable, what is the logic for changing the components that make up the age?Second, every time you get the value, you are firing the
PropertyChanged
event, which is not good.Your
Roster
class should look like this:Now, when the properties in the list items are changed, the parent object will fire the property changed event, and anything bound to it should change as well.