WPF Databinding - am I doing this wrong? | Tech Off

jh71283
Throw new System.Beverage. OutOfCoffeeException()

I have set up a DependencyProperty, and bound a label to it.

On my class I implement INotifyPropertyChanged, and in the Set method of the DP, I call NotifyPropertyChanged.

However it's pretty slow, like it will take 2 or 3 seconds to change the label.

I know that it is not a delay in sending the notify, because I cheated and set the label from codebehind on the line After the notify, and it updated immediately, so it does seem to be the databinding update that it taking the time Sad

stevo_
Casablanca != Manchester

Could you possibly show some code?

jh71283
Throw new System.Beverage. OutOfCoffeeException()

In reply to stevo_

#Aug 29th @ 1:48 AM

Partial Public Class SalesMode
    Inherits System.Windows.Window
    Implements System.ComponentModel.INotifyPropertyChanged
    Public Event PropertyChanged As System.ComponentModel.PropertyChangedEventHandler _
     Implements System.ComponentModel.INotifyPropertyChanged.PropertyChanged

    Private Sub NotifyPropertyChanged(ByVal info As String)
        RaiseEvent PropertyChanged(Me, New System.ComponentModel.PropertyChangedEventArgs(info))
    End Sub

.....

    Dim _CurrentPriceGroupName As String
    Dim CurrentPriceGroupNameProperty As Windows.DependencyProperty ' Gets registered in the form initializer.

    Public Property CurrentPriceGroupName() As String
        Get
            Return _CurrentPricegroupName
        End Get
        Set(ByVal value As String)
            _CurrentPriceGroupName = value
            NotifyPropertyChanged("CurrentPriceGroupName")

            ' lblPriceGroup.Content = value
        End Set
    End Property

wkempf

DPs do their own change notification. You shouldn't be using INotifyPropertyChanged.

stevo_
Casablanca != Manchester

In reply to wkempf

#Aug 29th @ 9:02 AM

The getter and setter should be using the DependencyProperty as a key on the DependencyObject (of which Window is)..

Something like:

public static readonly DependencyProperty SomethingProperty = DependencyProperty.Register("Something", typeof(int), etc)

public int Something
{
get
{
return (int)GetValue(SomethingProperty);
}
set
{
SetValue(SomethingProperty, value);
}
}

edit: added readonly

wkempf

In reply to stevo_

#Aug 29th @ 9:34 AM

Yeah, I didn't read his code, only the first post, where it was obvious what at least some of his problem is. Sounds like the OP doesn't yet understand DPs. I'd suggest focusing on the documentation of DPs for a while, or better yet, picking up a WPF book and reading about the concept.

stevo_
Casablanca != Manchester

In reply to wkempf

#Aug 29th @ 11:08 AM

Yes sorry I didn't mean to quote you, still not used to channel9s reply buttons yet.. and you are correct the op does sound like he's new to the dependency system but code is so much easier to read-debug.. english is overrated and verbose Wink

jh71283
Throw new System.Beverage. OutOfCoffeeException()

In reply to stevo_

#Aug 29th @ 11:18 AM

fair enough, but without the notifychanged, the label never updated.

It seems that I am not alone in my ignorance either...
http://blogs.microsoft.co.il/blogs/dorony/archive/2007/08/31/WPF-Binding_2C00_-INotifyPropertyChanged-and-Linq.aspx

but thanks for the sample stevo - will try that out.

jh71283
Throw new System.Beverage. OutOfCoffeeException()

In reply to jh71283

#Aug 29th @ 12:03 PM

it works, but there is still a delay. how strange.

stevo_
Casablanca != Manchester

In reply to jh71283

#Aug 29th @ 12:03 PM

Well you use INotifyPropertyChanged on business objects (those that cannot or shouldn't be a dependency object), it lets them work nicely with a lightweight interface.. the blog post is interesting though, using linq expressions to specify the property that changed.. would help with refactoring and avoiding bugs.. not sure if it has any realistic perf hits..

I would suggest stepping through the program when you are changing the object because I've not heard of any issues myself.. this could well be related to something else.

jh71283
Throw new System.Beverage. OutOfCoffeeException()

In reply to stevo_

#Aug 29th @ 12:23 PM

Yeah I will look and see if there is something in the background, however as I said - if I manually tell the label to change, it does so immediately, so i know that the property itself is being set at the correct time, it's just the UI that lags.

vesuvius
Everyone has talent at twenty-five. The difficulty is to have it at fifty.

In reply to jh71283

#Aug 29th @ 12:03 PM

INotifyPropertyChanged implements a delegate that has a string as a parameter. If he did not want to use the INotifyPropertyChanged interface, why not create his own delegate that passes in refactorable data types instead of strings?

I hate using strings as well, and almost always use enums in their place. You can then pass these user defines types how ever many you need into the delegate you create. Problem solved.

wkempf

In reply to vesuvius

#Aug 30th @ 12:53 AM

Because such a delegate wouldn't be used by the databinding framework. Problem not solved.