Question

Newbie question.

I have two c# classes – a code class (say, CodeClass) and a form class (say, FormClass). In CodeClass I have a number of functions which I will use to periodically update a string within the class (I can use a property or whatever is appropriate). I want some way of notifying other classes when this string value changes. i.e., I’ll try to have FormClass subscribe to change events on string message and then print the value to a text box or similar. However, at some point in the future, I need to provide API functions from CodeClass – so basically I need a way to notify any subscribing class of changes in the string message (string message does not get modified anywhere outside CodeClass – it happens within functions in CodeClass). I have tried with events and delegates etc but these all seem to be implemented by an external class modifying the string message (property).

Regards, etc

Answer 1

You need to implement the INotifyPropertyChanged interface:

class CodeClass : INotifyPropertyChanged
{

    private string _myProperty;
    public string MyProperty
    {
        get { return _myProperty; }
        set
        {
            _myProperty = value;
            OnPropertyChanged("MyProperty");
        }
    }

    #region INotifyPropertyChanged implementation

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        var handler = PropertyChanged;
        if (handler != null)
        handler(this, new PropertyChangedEventArgs(propertyName));
    }

    #endregion

}

In FormClass, you can subscribe to the PropertyChanged event like this:

codeClass.PropertyChanged += codeClass_PropertyChanged;

...

void codeClass_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
    if (e.PropertyName = "MyProperty")
    {
        ...
    }
}