Start Wpf command canexecute not updating

Wpf command canexecute not updating

Basically it guesses all the possible events where your data could be changed.

Now that it's working, I can't re-apply the vote again. I had the same problem happening when I was changing the content of a Texbox from the code-behind. In this app, they had the texbox being edited by a control that would popup, and when you saved the popup, it would change the Texbox. Requery Suggested = value; I was getting a near constant/looping evaluation of my Can Execute code for some reason.

Did you try to raise INotify Property Changed for the Command?

Could you please explain where i went wrong or miss understood the ICommand implementation. Updated Relay i Command code I use: #Region "Declarations" Private Read Only _Can Execute As Func(Of Boolean) Private Read Only _Execute As Action #End Region #Region "Constructors" Public Sub New(By Val execute As Action) Me. Requery Suggested, value End If End Add Handler Remove Handler(By Val value As Event Handler) If _Can Execute Is Not Nothing Then Remove Handler Command Manager. In a large system with lots of commands, this can be very very slow!

ID, False)) End If End Sub Public Sub Delete Address() If Is Nothing(Selected Address) = False Then Try Contact. Remove(Selected Address) Catch ex As Exception Msg Box("Address not found") End Try End If End Sub Public Function Can Delete Address() If Is Nothing(Selected Address) Then Return False Else Return Contact. Contains(Selected Address) End If End Function End Class The problem is that the Canexecutechanged is firing only at start, I actually want to get the delete button enabled only when something in the listbox is selected, and I want to get it done by MVVM - ICommand binding method. Can Execute Changed Add Handler(By Val value As Event Handler) If _Can Execute Is Not Nothing Then Add Handler Command Manager. Invoke() End Sub #End Region End Class After thorough googling or MSDN searching on relay command the core difference between it and ICOMMAND found that raise event is forced to requery canexecute status, and the code to force is "Command Manager. because although this works functionally, and is ok for small applications, it is indiscriminate and will potentially re-query every command!

Public Class Delete Command Implements ICommand Private method As Object Private methodname As String Public Sub New(By Val Controlname As String, By Val mee As Object) methodname = Controlname method = mee End Sub Public Function Can Execute(parameter As Object) As Boolean Implements ICommand. Can Delete Address() Case "Numbers" Return Try Cast(method, Model View. Can Execute Changed Public Sub Execute(parameter As Object) Implements ICommand. Delete Address() Case "Numbers" Try Cast(method, Model View. Add Command("Address", Me) Property Delete Address Command As New Commands.

Can Execute Select Case methodname Case "Address" Return Try Cast(method, Model View. Execute Select Case methodname Case "Address" Try Cast(method, Model View. Delete Command("Address", Me) Property Selected Address As Model.

I really hope this helps somebody, and saves them the hours I just wasted.

; are you implying that the currently active window in the OS is not this programs window?

You don't need to have a field for the Command, just return new one each time. Or create new Command only for the case when you need the forcing.

Not necessarily, as that may make your class hard to test. Another option is to add a method to Relay Command that allows you to raise Can Execute Changed just for that command (Command Manager.

Invalid Requery Suggested invalidates all commands, which is somewhat of an overkill).