Why isn't my ItemsControl showing my ViewModels? - wpf

Question

I am trying to populate a page with a list of items from my database. I have created models and viewmodels for these items, but they are not showing up in my ItemsControl.
I have a Model, which has a corresponding ViewModel that implements INotifyPropertyChanged.
Model:
Public Class ItemModel
Private _year As String
Public Property Year As String
Get
Return _year
End Get
Set(value As String)
_year = value
End Set
End Property
Public Sub New()
_year = Now.Year & "-" & (Now.Year + 1)
End Sub
Public Function ToString() As String
Return _year & " Item Model"
End Function
End Class
ViewModel:
Imports System.ComponentModel
Public Class ItemViewModel
Implements INotifyPropertyChanged
Private _currentItem As ItemModel
Public Property CurrentItem As ItemModel
Get
Return _currentItem
End Get
Set(value As ItemModel)
If _currentItem IsNot value Then
_currentItem = value
NotifyPropertyChanged("CurrentItem")
End If
End Set
End Property
Public Sub New()
_currentItem = New DciSurveyModel()
End Sub
Public Function ToString() As String
Return _currentItem.Year & " Item ViewModel"
End Function
Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
Private Sub NotifyPropertyChanged(Optional ByVal propertyName As String = Nothing)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
End Sub
End Class
I bind the ItemsControl to an ObservableCollection of ViewModels, but the ViewModels do not appear. I have tried using an ItemsTemplate to create a textbox setting the Text={Binding Path=CurrentItem.Year} to no avail.
XAML:
<Page x:Class="ItemPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300"
Name="ItemPage"
Title="ItemPage" Loaded="Page_Loaded_1" Margin="10">
<Grid>
<ItemsControl ItemsSource="{Binding Path=ItemCollection}" />
</Grid>
</Page>
Here is the code-behind:
Imports OClient = Oracle.DataAccess.Client
Imports System.Collections.ObjectModel
Imports System.Data
Class ItemPage
Private ds As DataSet
Private itemsTable As DataTable
Public Property ItemsCollection As ObservableCollection(Of ItemViewModel)
Private Sub Page_Loaded_1(sender As Object, e As RoutedEventArgs)
Dim itemsQry = "select item_year from items order by item_year desc"
Dim queryCmd As New OClient.OracleCommand(itemsQry, O.con)
Dim adapter As New OClient.OracleDataAdapter(queryCmd)
ds = New DataSet
adapter.Fill(ds, "items")
itemsTable = ds.Tables("items")
ItemsCollection = New ObservableCollection(Of ItemViewModel)
For Each r As DataRow In surveys.Rows
Dim newItem As New ItemViewModel
newItem.CurrentItem.Year = r.Item("ITEM_YEAR").ToString
Next
Me.DataContext = Me
End Sub
End Class
I am having a very hard time figuring out where my app is falling apart. Is it in my implementation of the ViewModels? Am I not binding the data correctly? Do I need to do something different with my ObservableCollection?
Thanks for helping a newbie.

Answer 1

You iterate over the elements of surveys.Rows and create a new ItemViewModel for each one, but you never add them to ItemsCollection, by ItemsCollection.Add(newItem):
For Each r As DataRow In surveys.Rows
Dim newItem As New ItemViewModel
newItem.CurrentItem.Year = r.Item("ITEM_YEAR").ToString
ItemsCollection.Add(newItem)
Next
You're also using a wrong Path for the ItemsSource Binding. It must be ItemsCollection instead of ItemCollection.
Besides that, instead of overriding ToString() you should declare a DataTemplate:
<ItemsControl ItemsSource="{Binding ItemsCollection}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBlock
Text="{Binding CurrentItem.Year, StringFormat={}{0} Item ViewModel}"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>