Custom Event in Custom Control (on variable changed)

Question

I'm making a custom control including three buttons. Every button represents a tab. When I click a button to change to the tab corresponding to that tab a variable for the controll is uppdated, this variable is called "selectedIndex". How can I make a custom event that triggers when this index is changed?

I've seen solutions for custom events here but all of them is copies of already existing events such as Click-events. My problem involvs having an event on variable change".

Regards!

Is that variable a property on the object? The object could implement INotifyPropertyChanged as a standard interface and invoke the PropertyChanged event in the property's setter. — David
– David, Commented Jun 10, 2014 at 9:37
Wery good idea, I will look in to how to make my variable a property. Thanks! — Dave
– Dave, Commented Jun 10, 2014 at 9:51
So I added a property for IndexCHanged: public int SelectedIndex { get; private set; //set { selectedIndex = value; } } Now, how do I add INotifyPropertyChanged for only this property so that it triggers an event when the value is changed? — Dave
– Dave, Commented Jun 10, 2014 at 11:16

David · Accepted Answer · 2014-06-10 12:07:14Z

2

One option is to have your object implement the very standard INotifyPropertyChanged interface. There's no rule which states that every property on an object needs to raise the PropertyChanged event, so just raise it for the one property in question. Something like this:

public class MyObject : INotifyPropertyChanged
{
    private string _myProperty;
    public string MyProperty
    {
        get { return _myProperty; }
        set
        {
            _myProperty = value;
            NotifyPropertyChanged();
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

If your .NET version doesn't support CallerMemberName then you can remove that and supply the property name manually:

NotifyPropertyChanged("MyProperty");

At this point any calling code can subscribe to the public PropertyChanged event on any instance of this object. This interface is particularly handy because it's commonly used in lots of UI technologies for updating data-bound UI elements. All the interface enforces, really, is a standard name for the event. If you'd prefer, you can forgo the interface and just create a custom public event. And just invoke that event any time your object logically needs to. The structure of exposing an event and invoking it would be the same.

answered Jun 10, 2014 at 12:07

David

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1 Comment

Dave Over a year ago

Thanks alot mr! I would like to make your first comment the answer as it is actually a good and straight forward answer to my question. But because I can't as it is only a comment I will mark your other response as the answer! Have a wonderful day!

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