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C# WPF reach an object in ObservableCollection by binding a TreeViewItem

Im working on a WPF project trying to get information from an ImpactElement-object. That object is inside a ObservableCollection called ElementList. This ElementList is located inside another ObservableCollection called ListOfCreatedStacks that holds objects of the Class Stack.
It only shows the toString from the element (ImpactElement) inside ElementList. I want the ImpactElements variable ElementMark to be shown from each elemnt in ElementList.
This is how it looks right now One element added in the ElementList
I can create any numbers of Stack and inside each stack there´s a ElementList with different numbers of ImpactElement. Two stacks with different amount of ImpactElements in the ElementList
From these pictures you can see that each ImpactElement from the ElementList is shown as "IMPACT_Visual_Stacker.Model.ImpactElement" but i want it to be the variable ElementMark that is inside ImpactElement Class.
Here´s the code from different Classes.
public class Controller
{
public ObservableCollection<Stack> ListOfCreatedStacks { get { return listOfCreatedStacks; } set { listOfCreatedStacks = value; } }
}
public class Stack
{
public ObservableCollection<ImpactElement> ElementList { get { return elementList; } set { elementList = value; } }
public string Id { get { return id; } set { id = value; } }
}
public class ImpactElement
{
private string elementMark;
private int id;
private Vector3 sizeLWH;
private Vector3 positionXYZ;
private Vector3 rotationXYZ;
private Mesh elementMesh;
}
Here´s the XAML part.
<ListView ItemsSource="{Binding ListOfCreatedStacks}" HorizontalAlignment="Left" Margin="350, 200,0,0" Width="300">
<ListView.ItemTemplate>
<DataTemplate>
<TreeViewItem
Header="{Binding Id}"
IsExpanded="True">
<TreeViewItem
ItemsSource="{Binding ElementList}" Header="{Binding ElementMark}" IsExpanded="True">
</TreeViewItem>
</TreeViewItem>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
I've tried a solution from the other StackOverflow i got from Ed.
The result ends up with only adding a Hiearchy object insted of my "ImpactElement"-objects.
This is what the tested XAML looks like :
<ListView ItemsSource="{Binding ListOfCreatedStacks}" HorizontalAlignment="Left" Margin="350, 200,0,0" Width="300">
<ListView.ItemTemplate>
<HierarchicalDataTemplate DataType="{x:Type System:String}"
ItemsSource="{Binding ListOfCreatedStacks}">
<TreeViewItem
Header="{Binding Id}"
IsExpanded="True">
<HierarchicalDataTemplate DataType="{x:Type System:String}"
ItemsSource="{Binding ElementList}">
<TreeViewItem
Header="{Binding ElementMark}"
IsExpanded="True">
</TreeViewItem>
</HierarchicalDataTemplate>
</TreeViewItem>
</HierarchicalDataTemplate>
</ListView.ItemTemplate>
</ListView>
Feels like a miss some easy part that i dont understand. Thanks for the help.

First, Controller, ElementList, and ImpactElement should probably be implementing INotifyPropertyChanged. You can find a million examples of that on Stack Overflow and elsewhere. It's simple, and you can get help here if you run into any snags.
What that will do is cause the UI to update if you change any bound property values on those objects while they're visible in the UI. The ObservableCollections will notify the UI if you add or remove items, but they can't notify the UI if some property of one of items happens to change.
Second, ImpactElement has only private fields. Since the private fields were omitted on the other classes, I'm guessing this was just an oversight when you copied the code. But you can only bind to public properties. Must be public, must be a property with a get and usually a set.
I'm hoping that you've assigned an instance of Controller to your DataContext. If you didn't, the tree won't populate.
I found WPF's TreeView baffling at first, and I wasn't new to XAML when I first looked at it. Do a bunch of simple examples (and come here for help if you need it), don't just paste in the XAML I gave you. It'll snap into focus.
Finally, you did a lot of things in your XAML that weren't done in the example. I don't know why you did those things, but you can't just go doing stuff at random. It doesn't work well. But as I said the learning curve on this one is tough, so no harm done.
So here's the XAML:
<TreeView
ItemsSource="{Binding ListOfCreatedStacks}"
HorizontalAlignment="Left"
Margin="350, 200,0,0"
Width="300">
<TreeView.ItemContainerStyle>
<Style
TargetType="TreeViewItem"
BasedOn="{StaticResource {x:Type TreeViewItem}}"
>
<Setter Property="IsExpanded" Value="True" />
</Style>
</TreeView.ItemContainerStyle>
<TreeView.ItemTemplate>
<HierarchicalDataTemplate
DataType="{x:Type local:Stack}"
ItemsSource="{Binding ElementList}"
>
<Label Content="{Binding Id}" />
<HierarchicalDataTemplate.ItemTemplate>
<HierarchicalDataTemplate
DataType="{x:Type local:ImpactElement}"
>
<Label Content="{Binding ElementMark}" />
</HierarchicalDataTemplate>
</HierarchicalDataTemplate.ItemTemplate>
</HierarchicalDataTemplate>
</TreeView.ItemTemplate>
</TreeView>
So the TreeView's ItemsSource is ListOfCreatedStacks.
We give the TreeView an ItemContainerStyle which will apply to every TreeViewItem in the tree. We only do that so we can set IsExpanded. There's no other way to get to the TreeViewItems. We could also give the top-level item template an ItemContainerStyle of its own, which would only affect its children, if we wanted to do something different with those. But we don't need to.
And we give the TreeView an ItemTemplate. That is how we show a TreeViewItem how to display one of the TreeView's children. When you look at the HierarchicalDataTemplate, it's a bit like a TreeView: It's got an ItemsSource, which we bind to a property of Stack which contains the children of the Stack. It has an ItemTemplate for its own children. It could, as I said, have an ItemContainerStyle, but we'll just let it inherit the one we set on the TreeView.
It's recursive: A tree node is very much like a whole tree.
If you don't give a HierarchicalDataTemplate an ItemTemplate of its own, the TreeViewItems it applies to will just use that one as the template for their own children, and the children will do the same. If you gave ImpactElement a child collection of ImpactElements, the tree could be two dozen levels deep without making a single change in the XAML above.
Any DataTemplate or HierarchicalDataTempate can have a DataType property. That is the type of viewmodel item being displayed by the template. I don't know where you got System:String from.
In this particular case1, DataType serves no purpose but to help you keep things straight when you're editing the XAML: It reminds you which template at which level of recursion applies to which collection item, and he's Intellisense help you out as well.
Finally, we have the content of the HierarchicalDataTempate:
<Label Content="{Binding Id}" />
That could be any single XAML element, but it could be a Grid or a StackPanel containing a whole UI if you wanted. You can put anything in there. You could put a whole different TreeView in there.
Lastly, you should learn to do layout with StackPanel and Grid columns and rows. This margin business is a nightmare if you want to rearrange anything. I presume you're using the Design mode in VS? All I use that for is to preview what I've done by hand in the XAML. Properly done, in XAML layout everything's positioned relative to its parent and siblings. Maybe it has a fixed width and/or height, usually a small margin -- single digits -- just to create space between neighbors, not for absolute positioning. Once you get used to it, it's a really nice way to work with stuff. A lot like HTML.
1 For the other uses of the DataType property of a DataTemplate or HierarchicalDataTemplate, see "implicit datatemplates", and here's a more complicated example for doing it with treeview items. If you're already struggling to digest all this, don't go look at that stuff, just focus on the case I gave you above. That's more than enough. Data templates are a learning curve, and adding recursion just makes everything weirder.

Caliburn.Micro: Grid not getting binded/linked to x:Name

So I'm developing a Windows Phone 8 app with the Caliburn.Micro framework. I'm trying to create a grid where I, at runtime add/remove elements such as TextBlock's at runtime. I've tried a few things to bind my code to the x:Name but nothing has worked so far.
So one of the things i tried was having a placeholder grid in my xaml aka View:
<Grid x:Name="ContentPanel" Margin="0,97,0,0" Grid.RowSpan="2">
</Grid>
And then i my ViewModel i use the following to bind my ContentPanel Grid:
private Grid contentPanel;
public Grid ContentPanel
{
get
{
return contentPanel;
}
set
{
contentPanel = value;
NotifyOfPropertyChange(() => ContentPanel);
}
}
I then created a TextBlock to add to the grid:
TextBlock txt1 = new TextBlock();
txt1.Text = "2005 Products Shipped";
txt1.FontSize = 20;
txt1.FontWeight = FontWeights.Bold;
Grid.SetRow(txt1, 1);
And finally i added the TextBlock to my Grid:
ContentPanel.Children.Add(txt1);
When i run this code ContentPanel turn out to be equals null, why is that? Shouldn't Caliburn auto bind ContentPanel x:Name="ContentPanel" with the property ContentPanel?
I would appreciate your help in this matter.
My core problem, that i need solved is this:
I got a login page in my app where i show some pictures and text loaded from a server. As you can see below this is done with Image and a TextBlock When that server is offline or the wi-fi simply aren't enabled i want to replace this picture+text with a static image. Aka i want to remove the TextBlock from the StackPanel.
The part where i load and show the stuff form my server works great and looks like this in my xaml:
<StackPanel Orientation="Horizontal" Background="White" DataContext="{Binding FeedItemsAnnounce,Mode=TwoWay}" >
<Image delay:LowProfileImageLoader.UriSource="{Binding ImagePath,Mode=TwoWay}" Margin="5" Width="170" Height="138">
<i:Interaction.Triggers>
<i:EventTrigger
EventName="Tap">
<cm:ActionMessage
MethodName="LoadAnnouncement">
<cm:Parameter Value="{Binding Link}"></cm:Parameter>
</cm:ActionMessage>
</i:EventTrigger>
</i:Interaction.Triggers>
</Image>
<TextBlock Text="{Binding Title}" TextWrapping="Wrap" Width="160" Foreground="Black" FontSize="24" VerticalAlignment="Center" Margin="25,0,0,0"></TextBlock>
<i:Interaction.Triggers>
<i:EventTrigger
EventName="Tap">
<cm:ActionMessage
MethodName="LoadAnnouncement">
<cm:Parameter Value="{Binding Link}"></cm:Parameter>
</cm:ActionMessage>
</i:EventTrigger>
</i:Interaction.Triggers>
So when the server is offline/wifi disabled i want to replace that with. so that the TextBlock is no longer there:
<Image delay:LowProfileImageLoader.UriSource="{Binding ImagePath,Mode=TwoWay}" DataContext="{Binding FeedItemsAdvertisement,Mode=TwoWay}" Margin="0,20,0,39" Width="380" Height="128">
<i:Interaction.Triggers>
<i:EventTrigger
EventName="Tap">
<cm:ActionMessage
MethodName="LoadAdvertisement" >
<cm:Parameter Value="{Binding Link}"></cm:Parameter>
</cm:ActionMessage>
</i:EventTrigger>
</i:Interaction.Triggers>
Is this even possible? If not what would the best semi-solution be?
EDIT 1: I've managed to setup the flow following the instructions from the accepted answer. But my BooleanToVisibilityConverter is not called, though my NotifyOfPropertyChange(() => IsConnectionAvailable); is getting called.
My Property:
private bool _isConnectionAvailable;
public bool IsConnectionAvailable
{
get { return _isConnectionAvailable; }
set
{
if (_isConnectionAvailable != value)
{
_isConnectionAvailable = value;
NotifyOfPropertyChange(() => IsConnectionAvailable);
}
}
}
How i change the bool: This code is called in my constructor for my ViewModel(just as a test to see if it was working):
IsConnectionAvailable = false;
TextBlock (without trigger code cause its the same as previous):
<TextBlock Text="{Binding Title}" Visibility="{Binding IsConnectionAvailable, Converter={StaticResource BoolToVisibility}}" TextWrapping="Wrap" Width="160" Foreground="Black" FontSize="24" VerticalAlignment="Center" Margin="25,0,0,0"></TextBlock>
It's like the Binding IsConnectionAvailable isn't working because i can change the name IsConnectionAvailable in my Xaml to anything and my NotifyOfPropertyChange(() => IsConnectionAvailable); will still be called.
Any ideas?
I can't even do a normal bind Visibility="{Binding Path=IsVisibil,Mode=TwoWay} to a public Visibility IsVisibil property. I've done this in other classes, but even this won't work??
EDIT 2: The problem that course the binding not to work, seems to lie somewhere in this code:
<StackPanel Orientation="Horizontal" Background="White" DataContext="{Binding FeedItemsAnnounce,Mode=TwoWay}" >
<Image delay:LowProfileImageLoader.UriSource="{Binding ImagePath,Mode=TwoWay}" Margin="5" Width="170" Height="138">
<i:Interaction.Triggers>
<i:EventTrigger
EventName="Tap">
<cm:ActionMessage
MethodName="LoadAnnouncement">
<cm:Parameter Value="{Binding Link}"></cm:Parameter>
</cm:ActionMessage>
</i:EventTrigger>
</i:Interaction.Triggers>
</Image>
<TextBlock Text="{Binding Title}" Visibility="{Binding Path=IsVisibil,Mode=TwoWay}" TextWrapping="Wrap" Width="160" Foreground="Black" FontSize="24" VerticalAlignment="Center" Margin="25,0,0,0"></TextBlock>
<i:Interaction.Triggers>
<i:EventTrigger
EventName="Tap">
<cm:ActionMessage
MethodName="LoadAnnouncement">
<cm:Parameter Value="{Binding Link}"></cm:Parameter>
</cm:ActionMessage>
</i:EventTrigger>
</i:Interaction.Triggers>
</StackPanel>
Solution to EDIT 1 and 2: I created an x:Name"Root" at the top of my xaml structure. Then changed the binding to:
ElementName=Root, Path=DataContext.IsVisibil
This is needed because the binding to visibility that I'm trying to set is inside another DataContxt.

This isn't the correct way to use CM, there are a number of areas where you are confusing the model and viewmodel and the binding functionality in CM.
What you are doing currently
You are attempting to have the CM framework look for a property called ContentPanel on your ViewModel and automatically figure out what properties on Grid to bind it to...
This won't work because of a few reasons:
I don't think there is a convention for Grid in CM - it's not really bindable in an obvious way (it's a layout container)
Grid is not a data enabled control - it doesn't know how to consume a collection and display dynamic rows out the box (it's a layout container)
What you are doing doesn't really make any sense (you have an instance of a grid in your UserControl and you have also instantiated a grid in your ViewModel - these are two separate instances of a control - you can't 'bind' them together - that's not how it all works)
CM and Bindings
When you using element name bindings e.g. x:Name with CM, it attempts to find a property on the ViewModel which matches the element name. At this point, depending on the conventions setup for the source control in question, CM will attempt to automagically wire up all the bits and pieces.
There are default conventions contained in ConventionManager which determine which properties to bind when you use element name bindings - e.g. for TextBlock, the Text property on the TextBlock is bound to the target property on the ViewModel.
http://caliburnmicro.codeplex.com/SourceControl/latest#src/Caliburn.Micro.Platform/ConventionManager.cs - look at the class constructor on ConventionManager to see the out of the box conventions - there isn't one for Grid
Once a target property is found, CM will bind it up.
(As an aside: it's worth noting that if the control type is a ContentControl CM will do some composition magic so you can have viewmodels that contain other viewmodels and have a composition all bound up at runtime - great for screens which have multiple sub-windows etc)
The problem you have is that there is no convention setup for Grid out of the box - this is most likely because a Grid in SL/WPF is primarily used for layout, and is not really a 'data container' or data aware in any way (apart from the few dependency properties you can bind to) - i.e. I don't think it's possible to bind to a grid and get a dynamic number of columns/rows without some customisation to the control, hence the omission of any conventions
(think about it - if you are binding a grid to a collection, what should the grid do... add rows or columns? It can't really be supported in a sensible way)
Now bringing it back to SL/WPF for a sec:
Usually if you want a variable list of items you will need to bind to the ItemsSource property of a control which inherits from ItemsControl (or ItemsControl itself).
Many controls do this: if they need to display a dynamic number of items they will usually inherit from ItemsControl.
How does this tie in with CM?
Caliburn Micro knows how to bind up ItemsControl out of the box. This means you can have a property on your ViewModel containing a collection of items and after binding you get a dynamic view of these at runtime
For example - a CM bound ItemsControl might look like this:
<ItemsControl x:Name="TextItems">
<!-- host the items generated by this ItemsControl in a grid -->
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Grid/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<!-- render each bound item using a TextBlock-->
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding SomeTextualProperty}"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
Now you just need a collection of objects to bind this to - each item in the collection becomes a new item in the control with its DataContext pointing to the bound item. I've made the assumption that you would want each item to be a ViewModel which contained the property SomeTextualProperty - I've defined that here...
// Provides a viewmodel for a textual item
public class TextItemViewModel
{
public string SomeTextualProperty { get; set;}
}
The VM that should contain the list of items would need to have a collection to bind against.
(Note: Since you are adding items to it at runtime you need to tell the UI when the collection changes - ObservableCollection gives you this for free as it implements collection changed notification events)
// This is the viewmodel that contains the list of text items
public class ScreenViewModel
{
public ObservableCollection<TextItemViewModel> TextItems { get; set; }
}
What else I would consider the incorrect approach
Your ViewModels shouldn't know about your View implementation i.e. they shouldn't reference any type of controls unless absolutely necessary (I can't think of a time when I had to put a control in a VM). ViewModels should model the view - but they shouldn't really need to know any specifics about what that view contains - this way they are more easily testable and they are easily reused
If you follow the above approach, you can get away with providing an application which re-uses the set of viewmodels, but provides different views for each. You can try this by replacing ItemsControl with another type of control in the view (as long as it's data aware such as a datagrid) and the VM will still work - the VM is view agnostic.
Your use of Grid in your VM is not ideal because Grid is a visual control, it is not data. Remember that the visuals are your View and the ViewModel should just contain data and events which notify the view of things happening
If I was doing this - the code would look more like the code I posted above.
To sum up
Model the information you wanted to show in a ViewModel (TextItemViewModel)
Add a collection of these objects to the main ViewModel (ScreenViewModel) using a change aware collection such as ObservableCollection
Add/remove items from the collection using the standard add/remove
Bind the ItemsControl in the view using x:Name bindings to the collection on your ScreenViewModel
Adding/removing items in the VM will fire property changed notifications. ItemsControl will watch for these events and update itself accordingly
Addendum
You could get away with just using an ObservableCollection<string> instead of a TextBlockViewModel but it's not clear if you want to add more properties to the items you are binding to the grid (such as IsHeading property for headings which you could then make bold/italic in the view)
If you want to just use strings just modify the DataTemplate to bind directly to the DataContext rather than a property on the DataContext
<ItemsControl x:Name="TextItems">
<!-- host the items generated by this ItemsControl in a grid -->
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Grid/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<!-- render each bound item using a TextBlock-->
<ItemsControl.ItemTemplate>
<DataTemplate>
**<TextBlock Text="{Binding}"/> <!-- Bind direct -->**
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
Edit:
Ok in your case it's quite simple - your ViewModel should simply model the state of the server:
public class LoginPageViewModel
{
public bool IsConnectionAvailable { get; set; } // or whatever your variable should be called
}
Then bind the visibility of the textblock to this using a converter:
<TextBlock Visibility="{Binding IsConnectionAvailable, Converter={StaticResource BooleanToVisibilityConverter}}">
You will need to declare the static resource for the converter somewhere (in the control itself or your main resources dictionary for example)
It looks like there is a converter already defined in System.Windows.Controls somewhere, but in case you can't find it the implementation is pretty simple (you could probably do this a bit better to guard against invalid input but for brevity I've kept it tiny):
public class BooleanToVisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return (bool) value ? Visibility.Visible : Visibility.Collapsed;
}
public object ConvertBack(object value, Type targetType, object parameter,CultureInfo culture)
{
throw new NotImplementedException();
}
}
You may also want to change the state from available/unavailable during the views lifecycle, so in that case you probably want to use the property changed events built in to PropertyChangedBase (which Screen also inherits) to let the view know when the property changes
private bool _isConnectionAvailable;
public bool IsConnectionAvailable
{
get { return _isConnectionAvailable; }
set
{
if (_isConnectionAvailable != value)
{
_isConnectionAvailable = value;
NotifyOfPropertyChange(() => IsConnectionAvailable);
}
}
}
Addendum 2
I prefer the terse CM syntax instead of being explicit when binding action messages - so your XAML would change from:
<Image delay:LowProfileImageLoader.UriSource="{Binding ImagePath,Mode=TwoWay}" DataContext="{Binding FeedItemsAdvertisement,Mode=TwoWay}" Margin="0,20,0,39" Width="380" Height="128">
<i:Interaction.Triggers>
<i:EventTrigger
EventName="Tap">
<cm:ActionMessage
MethodName="LoadAdvertisement" >
<cm:Parameter Value="{Binding Link}"></cm:Parameter>
</cm:ActionMessage>
</i:EventTrigger>
</i:Interaction.Triggers>
</Image>
To
<Image delay:LowProfileImageLoader.UriSource="{Binding ImagePath,Mode=TwoWay}" DataContext="{Binding FeedItemsAdvertisement,Mode=TwoWay}" Margin="0,20,0,39" Width="380" Height="128" cal:Message.Attach="[Tap] = [LoadAdvertisement($dataContext.Link)]"></Image>
(actually that might not be right with the $dataContext.Link part ... but then again it might be... see here: http://caliburnmicro.codeplex.com/wikipage?title=All%20About%20Actions&referringTitle=Documentation)

Get Listboxitem from listbox

Hi this should be faily simple, however I don't know what I am doing wrong. I've been looking all over the internet seeing people make this work, even followed the tutorial on MSDN still nothing has worked for me.
I want to Iterate over a ListBox, and get the ListBoxItems so I can find the DataTemplate that I have added to it.
This is my code behind.
private void SetListBoxDataTemplate(ListBox MyListBox)
{
try
{
foreach (CustomDataTemplateObject dataobject in MyListBox.Items)
{
ListBoxItem lbi = (ListBoxItem)(MyListBox.ItemContainerGenerator.ContainerFromItem(dataobject));
ContentPresenter myContentPresenter = FindVisualChild<ContentPresenter>(lbi);
DataTemplate dt = myContentPresenter.ContentTemplate;
TextBlock tb = (TextBlock)dt.FindName("ListBoxItemTextBlock1", myContentPresenter);
ComboBox cb = (ComboBox)dt.FindName("ListBoxItemComboBox1", myContentPresenter);
tb.Text = dataobject.Text;
cb.ItemsSource = dataobject.ListColors;
}
}
catch (Exception ex)
{
MessageBox.Show(""+ex);
}
}
XAML looks like this:
<DataTemplate x:Key="ListBoxItemDataTemplate1">
<StackPanel Orientation="Horizontal">
<Border BorderBrush="Black" BorderThickness="1 1 0 1" MinWidth="50">
<TextBlock Name="ListBoxItemTextBlock1" Background="{Binding ElementName=ListBoxItemComboBox1, Path=SelectedValue}" >
</TextBlock>
</Border>
<ComboBox Name="ListBoxItemComboBox1" />
</StackPanel>
</DataTemplate>*
<StackPanel>
<ListBox Name="ListBoxTest1" ItemTemplate="{DynamicResource ListBoxItemDataTemplate1}" />
</StackPanel>
I have tried with setting my itemtemplate to static to see if it works, and the method i'm calling from code behind, is called after I have populated my ListBoxs
My dataobject is NOT null, however when i call the line in my code behind, my lbi, ends up being null.
Any suggestions? thanks in advance!
FIRST UPDATE
This problem only occurs if i call the method in my constructor, so perhaps it's because it hasn't initialized the full group element section yet. However I want to do this as soon as possible. Am I perhaps forced to do it in a WindowLoaded event?
SECOND UPDATE
Code updated, Rachel's answer worked for iterating over my ListBoxItems, however the Listbox Has not fully rendered since i'm unable to reach the Datatemplate at this time. So MyListBox_GeneratorStatusChanged is not working for this problem, but it does get the ListBoxItems.

WPF's main thread runs items at different priority levels. Code that runs in the Constructor all gets run at Normal priority, while things like rendering the ListBox and it's items run at the Render priority level, which occurs after all Normal priority operations have finished.
This means that your entire Constructor gets run (including SetListBoxDataTemplate()) before your ListBox is even rendered and the items get generated.
If you want to run some code after the items are generated, use the ItemsContainerGenerator.StatusChanged event
// Constructor
MyListBox.ItemContainerGenerator.StatusChanged += MyListBox_GeneratorStatusChanged;
...
void MyListBox_GeneratorStatusChanged(object sender, EventArgs e)
{
// return if containers have not been generated yet
if (MyListBox.ItemContainerGenerator.Status != GeneratorStatus.ContainersGenerated)
return;
// remove event
MyListBox.ItemContainerGenerator.StatusChanged -= MyListBox_GeneratorStatusChanged;
// your items are now generated
SetListBoxDataTemplate(MyListBox);
}
What are you trying to accomplish with this method anyways? It is a bit unusual for WPF, and there may be a much better WPF way of accomplishing your task.
Updated based on new code added to Question
A much better method of setting your Text and ItemsSource properties is to make use of WPF's data bindings.
Your DataTemplate should look like this:
<DataTemplate x:Key="ListBoxItemDataTemplate1">
<StackPanel Orientation="Horizontal">
<Border BorderBrush="Black" BorderThickness="1 1 0 1" MinWidth="50">
<TextBlock Text="{Binding Text}" Background="{Binding ElementName=ListBoxItemComboBox1, Path=SelectedValue}" >
</TextBlock>
</Border>
<ComboBox ItemsSource="{Binding ListColors}" />
</StackPanel>
</DataTemplate>*
A DataTemplate is like a cookie cutter. It's used to make the UI objects, but is not part of the UI object itself. All it does is tell WPF that "When you go to render this object, render it using this XAML". So the way your XAML gets rendered is
<ListBoxItem>
<StackPanel>
<Border>
<TextBlock Text="{Binding Text}" />
</Border>
<ComboBox ItemsSource="{Binding ListColors}">
</StackPanel>
</ListBoxItem>
In addition, the DataContext behind your ListBoxItem is the item from the collection bound to ListBox.ItemsSource, which based on your code should be CustomDataTemplateObject. That allows the bindings from the DataTemplate to work
If you're new to WPF and struggling to understand how exact the DataContext works, I'd recommend reading this article of mine: What is this "DataContext" you speak of?.
To summarize, WPF has two layers to an application: the UI layer and the Data Layer (DataContext). When you perform a basic binding like above, you are pulling data from the data layer into the UI layer.
So your ListBoxItem has a data layer of CustomDataTemplateObject, and the TextBlock.Text and ComboBox.ItemsSource bindings are pulling data from the data layer for use in the UI layer.
I'd also highly recommend using a utility like Snoop which lets you view the entire Visual Tree of a running WPF application to see how items get rendered. Its very useful for debugging or learning more about how WPF works.

You're confusing two jobs and mixing them into one. First, get access to the ListBoxItem:
private void SetListBoxDataTemplate(ListBox MyListBox)
{
foreach (ListBoxItem listBoxItem in MyListBox.Items)
{
}
}
Now you can get the DataTemplate from the ListBoxItem:
foreach (ListBoxItem listBoxItem in MyListBox.Items)
{
ContentPresenter presenter = FindVisualChild<ContentPresenter>(listBoxItem);
DataTemplate dataTemplate = presenter.ContentTemplate;
if (dataTemplate != null)
{
// Do something with dataTemplate here
}
}
The FindVisualChild method can be found in the How to: Find DataTemplate-Generated Elements page on MSDN.
UPDATE >>>
To answer your edit, yes, the constructor will be too early to try to access these DataTemplates because the Framework won't have applied them to all of the objects by then. It is best to use the FrameworkElement.Loaded Event to do these kinds of things, as that is the first event that can be called after the controls have all been initialised.

Set LongListSelector

I'm developing a Windows Phone app to practice my knowledge within the control LongListSelector. One of the pages in the app, the middle one has this code:
<!--Panorama item two-->
<phone:PanoramaItem x:Name="tasksPage" Header="Tasks">
<!--Double line list with image placeholder and text wrapping using a floating header that scrolls with the content-->
<phone:LongListSelector Margin="0,-38,-22,2" ItemsSource="{Binding Items}" LayoutMode="List">
<phone:LongListSelector.ListHeaderTemplate>
<DataTemplate>
<Grid Margin="12,0,0,38">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<TextBlock Text="second item"
Style="{StaticResource PanoramaItemHeaderTextStyle}"
Grid.Row="0"/>
</Grid>
</DataTemplate>
</phone:LongListSelector.ListHeaderTemplate>
<phone:LongListSelector.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal" Margin="12,2,0,4" Height="105" Width="432">
<!--Replace rectangle with image-->
<Border BorderThickness="1" Width="99" Height="99" BorderBrush="#FFFFC700" Background="#FFFFC700"/>
<StackPanel Width="311" Margin="8,-7,0,0">
<TextBlock Text="{Binding LineOne}" TextWrapping="Wrap" Margin="10,0" Style="{StaticResource PhoneTextExtraLargeStyle}" FontSize="{StaticResource PhoneFontSizeLarge}" />
<TextBlock Text="{Binding LineTwo}" TextWrapping="Wrap" Margin="10,-2,10,0" Style="{StaticResource PhoneTextSubtleStyle}" />
</StackPanel>
</StackPanel>
</DataTemplate>
</phone:LongListSelector.ItemTemplate>
</phone:LongListSelector>
</phone:PanoramaItem>
Could someone please explain briefly what the DataBindings is and how to use them (I have done some research). Could I for instance bind the LongListSelector to a list in IsolatedStorage?
I have create a ListBox before in another app, loading content from IsolatedStorage into it, but I don't know if this is the right approach. Right now the items in the LongListSelector has a yellow image right left to it - can i do the same if I'm loading the content programatically from IsolatedStorage?
I know this might be a couple or three questions, but I think they're fairly simple to answer for someone experienced.
Thanks!

Your LongListSelector has a number of items inside. They are added there through data binding by binding the ItemsSource to items which are a part of Items collection. This collection can be a List<T> or more often ObservableCollection<T> because that way, if properly implemented, the changes in ObservableCollection will reflect in your LongListSelector. The T is the type of your item - for example, a class called Book. This collection needs to be defined as a part of the DataContext object, which you set on the whole page or a part of page.
Now, as I mentioned, the Items collection is probably full of items - objects defined to have certain properties. In your case, those properties are LineOne and LineTwo, which are probably strings.
You cannot directly bind to items in isolated storage. You first need to load those items into memory. Let's assume you have a list of items serialized to JSON or XML format in your isolated storage, which is one popular way of keeping the list in isolated storage. You need to load them into a collection (deserialize) and then bind to LongListSelector. It is the right approach, yes.
The yellow image/rectangle/border defined on the left is static, but it can be there, of course. It will simply be rendered there as a part of every item you have in your LongListSelector and it will not depend on the object which you bind to.
I suggest you read the following articles/questions and answers which may explain the concept of binding to a list easier for you to understand:
MSDN - Quickstart: Data binding to controls for Windows Phone
Stack Overflow - WP8 working with XML and LongListSelector
GeekChamp - The New LongListSelector control in Windows Phone 8 SDK
in depth

Simplest explanation (overlysimplified!) is that data binding is binding a property of an object to another property a control above, there's:
<TextBlock Text="{Binding LineOne}" ... />
That is functionally equivalent to something like this:
TextBlock t = new TextBlock();
SomeObject o = new SomeObject() { LineOne = "The value of line 1" };
t.Text = o.LineOne;
// and then a propertychange listener to update t.text if o.lineone ever changes
o.PropertyChanged += (s,e) => { if (e.PropertyName == 'LineOne') t.Text = o.LineOne; };
You can't bind directly to something in isolated storage, but you can have an object load its content from isolated storage, expose those items through an Items property and then set that as the data context of the LLS.
In cases like LongListSelector (or other ItemsControl types) the itemscontrol's ItemsSource property is bound to some collection of objects (like an ObservableCollection<T>, which makes its items update whenever the collection updates. And then a template inside the ItemsControl has bindings to the properties of the individual items in the collection.

WinRT hierarchical data displaying

I need to display hierarchical data like:
public class Element
{
public string Name { get; private set; }
public Element[] Elements { get; private set; }
}
It would be just vertical panel with rectangle (with Name) for each element. If element is clicked, its child elements are displayed below it (element is expanded). If one of them is clicked, its elements appear and so on.
I already googled this and found out that there is no HierarchicalDataTemplate and no treeview in WinRT.
So I started to do it by myself.
I created ItemsControl and DataTemplate DataTemplate1 for it. In DataTemplate1 I also create ItemsControl and set DataTemplate2 as ItemTemplate. In DataTemplate2, ItemTemplate is DataTemplate3 and so on. The last DataTemplate is without ItemsControl.
In buttons Click event I change Elements IsVisible property for any elements in DataModel (that is Element[]), so it is easy to perform any custom logic to expand/collapse elements.
<DataTemplate x:Key="DataTemplate2">
<StackPanel Visibility="{Binding IsVisible, Converter={StaticResource BooleanToVisibilityConverter}}">
<Button Style="{StaticResource ItemButtonStyle}"
Click="MenuElement_Click">
<TextBlock Style="{StaticResource ItemTextBlockStyle}" Text="{Binding Name}"/>
</Button>
<ItemsControl ItemsSource="{Binding Elements}" ItemTemplate="{StaticResource DataTemplate3}"/>
</StackPanel>
</DataTemplate>
<DataTemplate x:Key="DataTemplate1">
<StackPanel Visibility="{Binding IsVisible, Converter={StaticResource BooleanToVisibilityConverter}}">
<Button Style="{StaticResource ItemButtonStyle}"
Click="MenuElement_Click">
<TextBlock Style="{StaticResource ItemTextBlockStyle}" Text="{Binding Name}"/>
</Button>
<ItemsControl ItemsSource="{Binding Elements}" ItemTemplate="{StaticResource DataTemplate2}"/>
</StackPanel>
</DataTemplate>
It works fine, but the problem is that if I want to enable 10 levels of hierarchy, I have to copypast 10 datatemplates. And 11 level still will not be available.
I also tried to create DataTemplate in C# and manually apply DataTemplate for its ItemSource and so on, in recursive method.
But I found 2 problems.
I don't know actually how to create DataTemplate in metro (C#), because it has no VisualTree property. I can only make (var dt= new Datatemplate();) and I don't know how to change it.
If I read DataTemplate from XAML (var dateTemplateRoot = (DataTemplate)this.Resources["DataTemplate1"];)
I still can't find ItemsControl in it and change its DataTemplate.
Actually, I can use var content = dateTemplateRoot.LoadContent(); and then find ItemsControl by VisualTreeHelper, but I can't use content after that as DataTemplate (content has type DependencyObject).
So, actually I have 2 questions.
Is it a good approach to perform hierarchical dropdown list by "binding" all items and only switch Visibility property?
The second is - how to enable unlimited level of hierarchical nesting?

WinRT XAML Toolkit has a TreeView control now. Check it out: http://winrtxamltoolkit.codeplex.com/SourceControl/changeset/view/b0ee76bd6492#WinRTXamlToolkit/Controls/TreeView/TreeView.cs
Take care though - this is just a rough port from Silverlight Toolkit and might not work so well. Also if you are planning on releasing it as part of a Windows Store application - you would need to heavily restyle it unless your app is desktop-only since it is not very touch-friendly.