DataGrid is Not Updating Properly

Question

I have a DataGrid that should display a new item when it is added to the ItemsSource but that is not happening and I can't see the error.

The XAML:


	
	....

The ViewModel:

Private CurrentWalk As New Walk

Private _Walks As List(Of Walk)
Public Property Walks As List(Of Walk)
	Get
		Return _Walks
	End Get
	Set(value As List(Of Walk))
		_Walks = value
	End Set
End Property

Private ReadOnly Property _Save As New RelayCommand(Of Integer)(AddressOf DoSave, AddressOf CanSave)
Public ReadOnly Property Save As RelayCommand(Of Integer)
	Get
		Return _Save()
	End Get
End Property

Private Function CanSave(obj As Object) As Boolean
	Return CurrentWalk.IsDirty
End Function

Private Sub DoSave(obj As Object)
	<>
	CurrentWalk.Add()   'Adds CurrentWalk to a database
	Walks.Add(CurrentWalk)
	RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(NameOf(Walks)))
End Sub

Shouldn't that RaiseEvent cause the DataGrid to be updated?

Answer

Use ObservableCollection(of T) instead of List(of T).

ObservableCollection already implements the ability to notify the View of the addition or deletion of elements.

Answer

Hi,@ RogerSchlueter-7899. Welcome to Microsoft Q&A .

You could iterate through the WalksObservableCollection and update the corresponding items in the Walks list.

I added a method called UpdateWalksList that clears the Walks list and adds each item from the WalksObservableCollection. This method is called whenever the WalksObservableCollection is updated. Now, both Walks and WalksObservableCollection should stay in sync.

Whenever the data of dgTimes (WalksObservableCollection) is modified, the data of dgTimes1 (Walks) is also updated immediately.

codebehind:


Imports System.Collections.ObjectModel
Imports System.ComponentModel

Public Class ViewModel
    Implements INotifyPropertyChanged

    Public Sub New()
        PopulateData()
        WalksObservableCollection = New ObservableCollection(Of Walk)(Walks)
    End Sub
    Private Sub PopulateData()
        Walks.Add(New Walk() With {
            .Id = 1,
            .Name = "user1"
        })
        Walks.Add(New Walk() With {
            .Id = 2,
            .Name = "user2"
        })
        Walks.Add(New Walk() With {
            .Id = 3,
            .Name = "user3"
        })
        Walks.Add(New Walk() With {
            .Id = 5,
            .Name = "user4"
        })
        Walks.Add(New Walk() With {
            .Id = 6,
            .Name = "user5"
        })
    End Sub
    Private _walksObservableCollection As ObservableCollection(Of Walk)
    Public Property WalksObservableCollection As ObservableCollection(Of Walk)
        Get
            Return _walksObservableCollection
        End Get
        Set(value As ObservableCollection(Of Walk))
            _walksObservableCollection = value
            OnPropertyChanged(NameOf(WalksObservableCollection))
            UpdateWalksList()
        End Set
    End Property

    Private _Walks As List(Of Walk) = New List(Of Walk)()

    Public Property Walks As List(Of Walk)
        Get
            Return _Walks
        End Get
        Set(value As List(Of Walk))
            _Walks = value
            OnPropertyChanged(NameOf(Walks))
            UpdateObservableCollection()
        End Set
    End Property

    Private Sub UpdateObservableCollection()
        WalksObservableCollection.Clear()
        For Each walk In Walks
            WalksObservableCollection.Add(walk)
        Next
    End Sub

    Private Sub UpdateWalksList()
        Walks.Clear()
        For Each walk In WalksObservableCollection
            Walks.Add(walk)
        Next
    End Sub
    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged

    Private Sub OnPropertyChanged(ByVal propertyName As String)
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
    End Sub
End Class
Public Class Walk
    Implements INotifyPropertyChanged
    Private Property _Id As Integer
    Public Property Id As Integer
        Get
            Return _Id
        End Get
        Set(ByVal value As Integer)
            _Id = value
            OnPropertyChanged(NameOf(Id))
        End Set
    End Property

    Private _Name As String

    Public Property Name As String
        Get
            Return _Name
        End Get
        Set(ByVal value As String)
            _Name = value
            OnPropertyChanged(NameOf(Name))
        End Set
    End Property
    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged

    Private Sub OnPropertyChanged(ByVal propertyName As String)
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
    End Sub
End Class

Update: You could bind the UpdateCommand to the CellEditEnding event using the EventToCommand behavior in XAML.Here is an example using the System.Windows.Interactivity library, which is commonly used with MVVM scenarios.

Install the System.Windows.Interactivity NuGet package in your project.

codebedhind:


Public Class ViewModel
    Implements INotifyPropertyChanged

    Public Sub New()
        PopulateData()
       
    End Sub
    Private Sub PopulateData()
        Walks.Add(New Walk() With {
            .Id = 1,
            .Name = "user1"
        })
        Walks.Add(New Walk() With {
            .Id = 2,
            .Name = "user2"
        })
        Walks.Add(New Walk() With {
            .Id = 3,
            .Name = "user3"
        })
        Walks.Add(New Walk() With {
            .Id = 5,
            .Name = "user4"
        })
        Walks.Add(New Walk() With {
            .Id = 6,
            .Name = "user5"
        })
    End Sub
  

    Private _Walks As List(Of Walk) = New List(Of Walk)()

    Public Property Walks As List(Of Walk)
        Get
            Return _Walks
        End Get
        Set(value As List(Of Walk))
            _Walks = value
            OnPropertyChanged(NameOf(Walks))
        End Set
    End Property
    Private _SelectedItem As Walk

    Public Property SelectedItem As Walk
        Get
            Return _SelectedItem
        End Get
        Set(value As Walk)
            _SelectedItem = value
            OnPropertyChanged(NameOf(SelectedItem))
        End Set
    End Property

    Private _editCellCommand As ICommand
    Public ReadOnly Property EditCellCommand As ICommand
        Get
            If _editCellCommand Is Nothing Then
                _editCellCommand = New RelayCommand(AddressOf EditCell)
            End If
            Return _editCellCommand
        End Get
    End Property

    ' Implement the logic for updating List(Of Walk)
    Private Sub EditCell(parameter As Object)
        Dim e As DataGridCellEditEndingEventArgs = TryCast(parameter, DataGridCellEditEndingEventArgs)
        Dim editedItem As Walk = TryCast(e.Row.Item, Walk)

        If editedItem IsNot Nothing Then
            Dim index As Integer = Walks.IndexOf(editedItem)

            If index <> -1 Then
                Dim editedColumn As DataGridColumn = e.Column
                Dim propertyName As String = editedColumn.SortMemberPath
                Dim editedValue As Object = (TryCast(e.EditingElement, TextBox)).Text

                If propertyName = "Id" Then
                    editedItem.Id = Convert.ToInt32(editedValue)
                ElseIf propertyName = "Name" Then
                    editedItem.Name = editedValue.ToString()
                End If

                Walks(index) = editedItem
            End If
        End If
    End Sub
  
    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged

    Private Sub OnPropertyChanged(ByVal propertyName As String)
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
    End Sub
End Class
Public Class Walk
    Implements INotifyPropertyChanged
    Private Property _Id As Integer
    Public Property Id As Integer
        Get
            Return _Id
        End Get
        Set(ByVal value As Integer)
            _Id = value
            OnPropertyChanged(NameOf(Id))
        End Set
    End Property

    Private _Name As String

    Public Property Name As String
        Get
            Return _Name
        End Get
        Set(ByVal value As String)
            _Name = value
            OnPropertyChanged(NameOf(Name))
        End Set
    End Property
    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged

    Private Sub OnPropertyChanged(ByVal propertyName As String)
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
    End Sub
End Class

Public Class RelayCommand
    Implements ICommand

    Private ReadOnly _execute As Action(Of Object)
    Private ReadOnly _canExecute As Func(Of Object, Boolean)

    Public Sub New(execute As Action(Of Object), Optional canExecute As Func(Of Object, Boolean) = Nothing)
        _execute = execute
        _canExecute = canExecute
    End Sub

    Public Custom Event CanExecuteChanged As EventHandler Implements ICommand.CanExecuteChanged
        AddHandler(ByVal value As EventHandler)
            If _canExecute IsNot Nothing Then
                AddHandler CommandManager.RequerySuggested, value
            End If
        End AddHandler

        RemoveHandler(ByVal value As EventHandler)
            If _canExecute IsNot Nothing Then
                RemoveHandler CommandManager.RequerySuggested, value
            End If
        End RemoveHandler

        RaiseEvent(ByVal sender As Object, ByVal e As EventArgs)
            If _canExecute IsNot Nothing Then
                CommandManager.InvalidateRequerySuggested()
            End If
        End RaiseEvent
    End Event

    Public Function CanExecute(ByVal parameter As Object) As Boolean Implements ICommand.CanExecute
        If _canExecute Is Nothing Then
            Return True
        Else
            Return _canExecute(parameter)
        End If
    End Function

    Public Sub Execute(ByVal parameter As Object) Implements ICommand.Execute
        _execute(parameter)
    End Sub
End Class

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DataGrid is Not Updating Properly

2 answers