Can I have multiple instances of the same UserCont

Question

I am creating a Text Editor Type app. I can have multiple editors open via tabs. In my first try, I used simple TextBoxes to edit text. Everything worked ok. Then I created a UserControl encapsulating the text box + buttons to perform text manipulation eg. bold/italic etc. I found out that when I open different tabs, they all contain the same content. eg. In Tab1 i enter "hello world" that will appear in all tabs. There is "no separation" even though they are in different tabs

<Window.Resources>
    <DataTemplate DataType="{x:Type vm:EditorTabViewModel}">
        <me:MarkdownEditor />
    </DataTemplate>
</Window.Resources>

I then as a test, tried a textbox and the usercontrol together to see if I have the same problem.

<Window.Resources>
    <DataTemplate DataType="{x:Type vm:EditorTabViewModel}">
        <StackPanel>
            <me:MarkdownEditor Text="{Binding Content}" Height="360" />
            <TextBox Text="{Binding Content}" Height="360" />
        </StackPanel>
    </DataTemplate>
</Window.Resources>

I then discovered a few strange things. With a new document, where content should be nothing, my MarkdownEditor had "System.Windows.Controls.Grid" in its text box as it a Grid was bound to the text. Text simple TextBox works as expected. Also I still had the same problem with all UserControls in the app having the same content.

The XAML for the UserControl

<UserControl x:Class="MarkdownEditMVVM.Controls.MarkdownEditor.MarkdownEditor" ...>
    <Grid>
        <ToolBar Grid.Row="0">
            <Button Command="{x:Static local:Commands.PreviewCommand}">
                <Image Source="../../Images/16/zoom.png" />
            </Button>
            <!-- more buttons -->
        </ToolBar>
        <TextBox Grid.Row="1" x:Name="txtEditor" AcceptsReturn="True" Text="{Binding Path=Text, UpdateSourceTrigger=PropertyChanged}" />
    </Grid>
</UserControl>

Update

I discovered that this has something to do with the way I have usercontrols rendered in the tabs where tabs are bound to ObservableCollection<TabViewModel>

Suppose I have a TabViewModel even just a empty class

public class TabViewModel {}

Then in my Window

public partial class Window1 : Window
{
    protected ObservableCollection<TabViewModel> _tabs;
    protected ICollectionView _tabsCollectionView;

    public Window1()
    {
        InitializeComponent();
        this.DataContext = this;
        _tabs = new ObservableCollection<TabViewModel>();
        _tabs.Add(new TabViewModel());
        _tabs.Add(new TabViewModel());
        _tabsCollectionView = CollectionViewSource.GetDefaultView(_tabs);
    }

    public ICollectionView Tabs
    {
        get { return _tabsCollectionView; }            
    }
}

XAML

<TabControl ItemsSource="{Binding Tabs}" IsSynchronizedWithCurrentItem="True">
    <TabControl.ItemTemplate>
        <DataTemplate>
            <TextBlock />
        </DataTemplate>
    </TabControl.ItemTemplate>
    <TabControl.ContentTemplate>
        <DataTemplate>
            <TextBox />
        </DataTemplate>
    </TabControl.ContentTemplate>
</TabControl>

I have created a simple Visual Studio Project hosted @mediafire illustrating this problem. I have a feeling it got something to do with the TabViewModels or the Tab Data Templates

Update 2

I further tested the user control problem by adding another tab control, this time without the TabViewModel

<TabControl Grid.Column="1">
    <TabItem Header="Tab 1">
        <TextBox />
    </TabItem>
    <TabItem Header="Tab 2">
        <TextBox  />
    </TabItem>
</TabControl>

It all worked ok. update also posted to mediafire

Update 3

Made yet another finding. This time, I tested with a binding. things worked fine ...

<TabControl Grid.Column="2" ItemsSource="{Binding Tabs}" IsSynchronizedWithCurrentItem="True">
    <TabControl.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding TabTitle}" />
        </DataTemplate>
    </TabControl.ItemTemplate>
    <TabControl.ContentTemplate>
        <DataTemplate>
            <TextBox Text="{Binding Text}" />
        </DataTemplate>
    </TabControl.ContentTemplate>
</TabControl>

Update also posted @mediafire

Update 4

Ok now I did a more complete set of tests

• Row 0, Column 0: TextBox, Tabs bound to ObservableCollection<TabViewModel>. No Bindings for TextBox. Problem observed
• Row 0, Column 1: TextBox, Normal TabItems, Tabs not bound to ObservableCollection<TabViewModel>. No Binding for TextBox. No problems
• Row 0, Column 2: TextBox, Tabs bound to ObservableCollection<TabViewModel>. No Bindings for TextBox. No Problems
• Row 1, Column 0: UserControl, Tabs bound to ObservableCollection<TabViewModel>. No Bindings for UserControl. Problem observed
• Row 1, Column 2: UserControl, Tabs bound to ObservableCollection<TabViewModel>. Bindings for UserControl. Problem observed. Text bindings not working

Update @mediafire

Answer 1

Big Edit in response to updates

I can get your mediafire example to work correctly by taking the following steps:

1. Remove the dependency property Text from your user control - you don't need it

2. Change your ContentTemplate on the TabControl to the below. This causes the UserControl.DataContext property to be set to the tab item DataContext

    <DataTemplate>
         <local:UserControl1 />
    </DataTemplate>
   

3. Change your UserControl to the below. This binds the Text property to the UserControl.DataContext.Text property.

   <TextBox Text="{Binding Text}" />
   

4. Remove the line this.DataContext = this from the constructor of UserControl1 - this will obviously replace the DataContext for the user control.

This caused the tabs to be correctly bound with the expected values in the sample app you uploaded

---

Original Answer

You can have multiple instances of a UserControl - that isn't your problem here.

The reason you are seeing the "System.Windows.Controls.Grid" text is because in your UserControl you are binding the Text property to this.DataContext.Text instead of this.Text - the property of your UserControl.

I think what you want to do is change the TextBox binding in your user control to:

<TextBox Grid.Row="1" x:Name="txtEditor" AcceptsReturn="True"
Text="{Binding Path=Text,
        UpdateSourceTrigger=PropertyChanged,
        RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type me:MarkDownEditor}}}" />

Note: this relies on the me namespace being set up to point to wherever your MarkDownEditor is located

Answer 2

You might be interested in the Writer sample application of the WPF Application Framework (WAF). It shows how to implement a text processing application with multiple tab support by applying the MVVM pattern.