CODEWITHSUNDEEP
wpfeventsdata-binding
Nick
Nick

Reputation: 10499

How to catch a property changed event after binding

I have a custom UserControl:

public partial class CustomCtrl : UserControl
{
    public CustomCtrl()
    {
        InitializeComponent();
    }

    public string Prova
    {
        get { return (string)GetValue(ProvaProperty); }
        set 
        {
            SetValue(ProvaProperty, value); 
        }
    }

    public static readonly DependencyProperty ProvaProperty =
        DependencyProperty.Register("Prova", typeof(string), typeof(CustomCtrl));

}

I do this simple binding:

CustomCtrl c = new CustomCtrl();
TextBlock t = new TextBlock();
c.SetBinding(CustomCtrl.ProvaProperty, new Binding("Text") { Source = t });
t.Text = "new string";

Now c.Prova is "new string", but how can I catch in my CustomControl class the event informing me that Prova has changed?

Upvotes: 4

Views: 3702

Answers (2)

Colin Smith
Colin Smith

Reputation: 12550

Something like this (this will catch changes on all instances of CustomCtrl):

public static readonly DependencyProperty ProvaProperty =
    DependencyProperty.Register(
    "Prova",
    typeof(string),
    typeof(CustomCtrl),
    new PropertyMetadata( new PropertyChangedCallback(OnValueChanged) )
);

private static void OnValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    // This is called whenever the Prova property has been changed.
}

If "clients" of your CustomCtrl wanted to catch a change to that property for a specific instance then they could use:

CustomCtrl instanceofsomecustomctrl = .......

DependencyPropertyDescriptor descr = 
                  DependencyPropertyDescriptor.FromProperty(CustomCtrl.ProvaProperty, typeof(CustomCtrl));

if (descr != null)
{
    descr.AddValueChanged(instanceofsomecustomctrl, delegate
        {
            // do something because property changed...
        });
}

Upvotes: 3

Rayshawn
Rayshawn

Reputation: 2617

I think this is what you're looking for, you want an event onChangeHandler.

public partial class CustomCtrl : UserControl
{
public CustomCtrl()
{
    InitializeComponent();
}

public string Prova
{
    get { return (string)GetValue(ProvaProperty); }
    set 
    {
        SetValue(ProvaProperty, value); 
        OnPropertyChanged("Prova");
    }
}
protected void OnPropertyChanged(string prova)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(prova));
        }
    }
 //This portion could go in the class where the event takes place
 private delegate void UpdateDelegate(DependencyProperty dp, Object value);


}

Upvotes: 1

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