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Create an instance of a C# class from inside XAML

I have a working application that has been written in C#, and I now want to extend that application to allow the user to switch between viewing the application, and viewing a built in web browser (inside the same application window).
I also have a separate working web browser, that has also been written in C#.
I have just added the functionality to the original application to include 'tabbed' displays, where the original application will be displayed on the first tab, and a built in web browser on the second tab.
The 'tabbed' displays for the application have been created using XAML markup in Visual Studio. I now want to add an instance of the Web browser that has also been written in C# to the second tab that I have created in the XAML markup.
It would be something like:
<TabControl>
<TabItem Header="Browser">
<StackPanel>
<!-- Call/ instantiate the browser here -->
</StackPanel>
</TabItem>
</TabControl>
But I have no idea how I call/ create an instance of the browser from within the XAML markup...
The browser has been created using C#:
namespace Agent
{
public partial class Browser : Form
{
public Browser()
{
...
}
}
}
Can anyone explain to me how a create an instance of Browser inside the ` of the XAML markup?
Edit
Ok, so I have edited my XAML markup as recommended in the answer that's been suggested- I now have:
<Window ...
xmlns:Agent="clr-namespace:Agent"
...>
<Grid>
...
<TabControl>
<TabItem Header="R">
<StackPanel>
...
</StackPanel>
</TabItem>
<TabItem Header="Browser">
<Agent:Browser x:Name="Browser" />
</TabItem>
</TabControl>
</Grid>
</Window>
I have also updated my Browser.cs class, so that it is now extending UserControl, rather than Form:
public partial class Browser : UserControl{
However, I am getting a compile error on the line:
<Agent:Browser x:Name="Browser" />
which says:
The name "Browser" does not exist in the namespace "clr-namespace:Agent".
But clearly Browser does exist in Agent, as shown by the code I've included here... In fact, when typing the line <Agent:Browser x:Name="Browser />, when I typed the :, Browser was one of the options that came up in the autocomplete menu...
What am I doing wrong here? Why doesn't the compiler think that Browser exists inside Agent?

The key to instantiating any object in XAML is to make sure the namespace is declared. You can provide any XML prefix and assign it to your CLR namespace (ref) and it will act like a using statement. For example:
<TabControl xmlns:agent="clr-namespace:Agent">
<TabItem Header="Browser">
<StackPanel>
<agent:Browser/>
</StackPanel>
</TabItem>
</TabControl>
NOTE: your object has to extend UIElement (or one of its children) for it to work in a XAML tree. If your control is a WinForms control you either need to find the equivalent XAML control or wrap it in a WindowsFormsHost (ref).
WPF vs. WinForms
The purpose of this section is to help recognize which platform code is by namespace, as well as some of the trade-offs. I've used both and can say from experience that they each have good points and... not so good points.
WinForms classes live in the System.Windows.Forms namespace, and are available by referencing the System.Windows.Forms.dll assembly.
WPF classes live in the System.Windows and System.Windows.Controls namespaces, and are available by referencing a set of DLLs
WinForms rendering is immediate. That means you are working against bitmaps and you are responsible for clearing and redrawing stuff yourself (usually you can just call Invalidate()). If you do heavy image bit manipulation, WinForms is easier to work with.
WPF rendering is declarative. That means more work is offloaded to your GPU and you just tell it how to draw stuff. You can also use GPU render shaders for special effects. WPF has a nicer look out of the box, but it has a reputation for making easy things difficult but impossible things possible.
WinForms is easier to learn, but has a dated look out of the box.
WPF is built around data binding, enabling the UI to update in response to property values automatically. It's also able to be completely restyled, although that is quite an undertaking.
If you are just getting started, I'd go ahead and bite the bullet to start the heavier learning curve for WPF. It will provide a basic understanding that transfers to other platforms like Windows Store apps, etc.

Firstly you need to place that tag inside of your UserControl opening tag like so:
<UserControl x:Class="View.testControl"
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"
xmlns:Agent="clr-namespace:Agent">
Then you can use it like this:
<TabControl>
<TabItem Header="R">
<StackPanel>
...
</StackPanel>
</TabItem>
<TabItem Header="Browser">
<Agent:Browser x:Name="Browser" />
</TabItem>
</TabControl>
EDIT
From what you told me in the comments you will need to create a Custom Control in your WPF project. To do that you need to:
Right Click your Project;
Select Add New Item;
From Installed (which is in the left column) select WPF;
From the list in the middle column select Custom Control;
Now you can create that control in your XAML with xmlns attribute.
Here is a great example from msdn on how to create custom controls

Is it possible to use reflection directly in XAML

In my DB I have a table that contains different items of userControls with the attributes "ClassName", "AssemblyName" and "NameSpace" which are necesarry to init the instances using reflection.
My Idea was To get this collection from the DB, set the collection as the data-context and dynamically load these usercontrols into a tabcontrol. I could use a "tabItem" which would contain it and in runtime in the code behind load it. I guess it would be really handy and fancy if it could be done directly from XAML in a template.
I've been googleling for something similar, but found nothing without using code behind.
I was thinking something like the following
<TabControl.ContentTemplate>
<DataTemplate>
<xxxControl ClassName="{Binding ClassName}" AssemblyName="{Binding AssemblyName}" NameSpace="{Binding NameSpace}" />
</DataTemplate>
</TabControl.ContentTemplate>
I could make such a custom "xxxControl" but it would be a waste of time if something like that already exists. This way The GUI could be completly generated by the parameters in the DB.

You can do a lot of things in XAML using markup extensions, in this case you could create one that instantiates controls from the given information. For that it needs some dependency properties that can be bound, and in ProvideValue it would then get the assembly, construct the full name and instantiate it.
Usage:
<DataTemplate>
<me:Instance Assembly="{Binding AssemblyName}"
NameSpace="{Binding NameSpace}"
Class="{Binding ClassName}"/>
</DataTemplate>
Obviously you still have code-behind, but that is how it should be, imperative code does not belong in XAML at all.
Also i doubt that your data-base should contain information about UI controls...

Ugh. Don't control your UI from the database directly. The closest you should come (assuming you can't make significant architecture changes) IMO would be to load your DB entries into an IObservable in your VM and use a DataTemplateSelector to translate your collection into UI controls.

WPF Combobox binding: can't change selection

After wasting hours on this, following on the heels of my Last Problem, I'm starting to feel that Framework 4 is a master of subtle evil, or my PC is haunted.
I have three comboboxes and a textbox on a WPF form, and I have an out-of-the-box Subsonic 3 ActiveRecord DAL.
When I load this "edit record" form, the comboboxes fill correctly, they select the correct items, and the textbox has the correct text. I can change the TextBox text and save the record just fine, but the comboboxes CANNOT BE CHANGED. The lists drop down and highlight, but when you click on an item, the item selected stays the same.
Here's my XAML:
<StackPanel Orientation="Horizontal" Margin="10,10,0,0">
<TextBlock Width="80">Asset</TextBlock>
<ComboBox Name="cboAsset" Width="180"
DisplayMemberPath="AssetName"
SelectedValuePath="AssetID"
SelectedValue="{Binding AssetID}" ></ComboBox>
</StackPanel>
<StackPanel Orientation="Horizontal" Margin="10,10,0,0">
<TextBlock Width="80">Status</TextBlock>
<ComboBox Name="cboStatus" Width="180"
DisplayMemberPath="JobStatusDesc" SelectedValuePath="JobStatusID"
SelectedValue="{Binding JobStatusID}" ></ComboBox>
</StackPanel>
<StackPanel Orientation="Horizontal" Margin="10,10,0,0">
<TextBlock Width="80">Category</TextBlock>
<ComboBox Name="cboCategories" Width="180"
DisplayMemberPath="CategoryName"
SelectedValuePath="JobCategoryID"
SelectedValue="{Binding JobCategoryID}" ></ComboBox>
</StackPanel>
<StackPanel Orientation="Horizontal" Margin="10,10,0,0">
<TextBlock Width="80">Reason</TextBlock>
<TextBox Name="txtReason" Width="380" Text="{Binding Reason}"/>
</StackPanel>
Here are the relevant snips of my code (intJobID is passed in):
SvcMgrDAL.Job oJob;
IQueryable<SvcMgrDAL.JobCategory> oCategories = SvcMgrDAL.JobCategory.All().OrderBy(x => x.CategoryName);
IQueryable<SvcMgrDAL.Asset> oAssets = SvcMgrDAL.Asset.All().OrderBy(x => x.AssetName);
IQueryable<SvcMgrDAL.JobStatus> oStatus = SvcMgrDAL.JobStatus.All();
cboCategories.ItemsSource = oCategories;
cboStatus.ItemsSource = oStatus;
cboAsset.ItemsSource = oAssets;
this.JobID = intJobID;
oJob = SvcMgrDAL.Job.SingleOrDefault(x => x.JobID == intJobID);
this.DataContext = oJob;
Things I've tried:
Explicitly setting IsReadOnly="false" and IsSynchronizedWithCurrentItem="True"
Changing the combobox ItemSources from IQueryables to Lists.
Building my own Job object (plain vanilla entity class using INotifyPropertyChanged).
Every binding mode for the comboboxes.
ItemsSource="{Binding}"
The Subsonic DAL doesn't implement INotifyPropertyChanged, but I don't see as it'd need to for simple binding like this. I just want to be able to pick something from the dropdown and save it.
Comparing it with my last problem (link at the top of this message), I seem to have something really wierd with data sources going on. Maybe it's a Subsonic thing?
EDIT: For some reason the set accessor is hit only on the AssetID property and only the first time. WPF is now heading for WTF :)
EDIT 2: You gotta be kidding me- I've removed the binding (ie it only has a displaymemberpath, a valuememberpath and an itemssouce) and it's STILL doing it! It accepts your first selection, and then won't change.

WPF Combo Boxes will not change the selected item if the currently selected item and the item that was just selected are considered equal by the object.Equals() method called on the newly selected object (i.e newlyslected.Equals(previoslySelected) ).
Overriding the Equals method on the class your binding the combobox items, should resolve the issue your are seeing.

I've narrowed it down to the Subsonic objects used as ComboBoxItems.
If you create a new class that uses exactly the same code as the relevant parts of the Subsonic one, it works.
If you use POCOs/datatables for the combos and Subsonic for the record being edited, it works.
But if you use Subsonic for both, it doesn't.
I had hoped to extend the subsonic objects and not have to code a full-blown BLL tier. Looks like I'm faced with doing that or throwing out Subsonic for the DAL. I might post a more specific question for the Subsonic folks.
Many thanks to all who contributed.

Old topic but I had the same problem and difficulty finding solution. This might help someone else.
Clue is above in WPF not detecting a different item has been seleted by user. (Symptom - event ComboBox_SelectionChanged only fires on first selection)
My scenario - lookup combo populated from IList built from a DISTINCT query. In this case the result of using NHibernate ICriteria.SetResultTransformer which only returns SOME fields, importantly NOT including the unique entity ID.
Solution - loop thru' IList after retrieval and give each entity a unique ID. WPF sees them as individuals and behaves appropriately.
Its only a value lookup - its the value content I was after.
The 'temporary' entities are never persisted. In this case it was a better approach than messing with overriding the object's Equals method for the sake of a simple GUI issue. An alternative would be to just copy or tranform the list into a format where WPF uses the value field to determine 'difference'...

Sounds like the field is somehow readonly, or that your change isn't being persisted. After the binding sets the new value, it will re-read the property to ensure that it was actually changed. If your property returns the old value, then it'll be re-selected in the combo box, giving the appearance that the value never changed.
I don't know that DAL, but can you step through the property setter code? You might also have an issue with type conversion.
EDIT reading your comment about the red rectangle -- it sounds as though your property (or something to do with the binding) is raising an exception. Unless, of course, you're using data validation in your UI. You might turn 'Break on all exceptions' in the debugger's settings, assuming you're using Visual Studio.
EDIT 2 You should check the VS Output pane for any error messages related to binding. You can also read this blog post which gives more info on debugging bindings.

It's hard to tell from a small sample of your code but try commenting out the line:
//this.DataContext = oJob;
and see if this helps.
Setting the DataContext and ItemsSource might be causing a conflict.

Did you write any global style for your combo box which may have a bug or something missing? Or are you using pure default styles for your combobox? Try removing any default styles applied.
Are you wiring up any events? If your code hooks up for event like PreviewMouseLeftButtonUp and marks event as handled then probably combobox may ignore and wont select anything.

Memory leak on CollectionView.View.Refresh

I have defined my binding thus:
<TreeView
ItemsSource="{Binding UsersView.View}"
ItemTemplate="{StaticResource MyDataTemplate}"
/>
The CollectionViewSource is defined thus:
private ObservableCollection<UserData> users;
public CollectionViewSource UsersView{get;set;}
UsersView=new CollectionViewSource{Source=users};
UsersView.SortDescriptions.Add(
new SortDescription("IsLoggedOn",ListSortDirection.Descending);
UsersView.SortDescriptions.Add(
new SortDescription("Username",ListSortDirection.Ascending);
So far, so good, this works as expected: The view shows first the users that are logged on in alphabetical order, then the ones that are not.
However, the IsLoggedIn property of the UserData is updated every few seconds by a backgroundworker thread and then the code calls:
UsersView.View.Refresh();
on the UI thread.
Again this works as expected: users that log on are moved from the bottom of the view to the top and vice versa. However: Every time I call the Refresh method on the view the application hoards 3,5MB of extra memory, which is only released after application shutdown (or after an OutOfMemoryException...)
I did some research and below is a list of fixes that did NOT work:
The UserData class implements INotifyPropertyChanged
Changing the underlying users collection does not make any difference at all: any IENumerable<UserData> as a source for the CollectionViewSource causes the problem.
-Changing the ColletionViewSource to a List<UserData> (and refreshing the binding) or inheriting from ObservableCollection to get access to the underlying Items collection to sort that in place does not work.
I am out of ideas! Help?
EDIT:
I found it:
The Resource MyDataTemplate contains a Label that is bound to a UserData object to show one of its properties, the UserData objects being handed down by the TreeView's ItemsSource. The Label has a ContextMenu defined thus:
<ContextMenu Background="Transparent" Width="325" Opacity=".8" HasDropShadow="True">
<PrivateMessengerUI:MyUserData IsReadOnly="True" >
<PrivateMessengerUI:MyUserData.DataContext>
<Binding Path="."/>
</PrivateMessengerUI:MyUserData.DataContext>
</PrivateMessengerUI:MyUserData>
</ContextMenu>
The MyUserData object is a UserControl that shows All properties of the UserData object. In this way the user first only sees one piece of data of a user and on a right click sees all of it.
When I remove the MyUserData UserControl from the DataTemplate the memory leak disappears! How can I still implement the behaviour as specified above?

Step one in troubleshooting memory leaks is to find the definitive source. This is not always obvious and can occasionally defy your intuition. Based on your explanation, if you remove your user control, the issue disappears, but when you put it back, you start leaking again. This very likely points to a memory leak within that control (though not necessarily). Perhaps your control fits into one of the many types of WPF memory leaks, or you have a more classic problem of subscribing to an event but not properly unwiring it when no longer needed (the weak event pattern is useful here).
Your best bet is to grab a tool like .NET Memory Profiler or ANTS Memory Profiler (both are excellent and have free trials). Use one of these tools find the objects that are hanging around after they should be gone. These tools provide help in tracing the chain of objects that are hanging onto your object. There are many good articles on memory profiling on their sites, here on SO and on the wide open web.

You could try 2 things:
First of all the DropShadow has some problems, as it hold some references that should be garbadge collected.. see this article for more information:
http://blog.ramondeklein.nl/index.php/2009/02/20/memory-leak-with-wpf-resources-in-rare-cases/
You can try to set th HasDropShadow to false, and see what happens with your memory.
Secondly, if we have multiple ContextMenu objects of the same menu, you might want to create a ContextMenu resource in your Resources, and reference it with the StaticResource extension like so:
<ContextMenu Background="Transparent" Width="325" Opacity=".8" x:Key="MyAwesomeContextMenu">
<PrivateMessengerUI:MyUserData IsReadOnly="True" >
<PrivateMessengerUI:MyUserData.DataContext>
<Binding Path="."/>
</PrivateMessengerUI:MyUserData.DataContext>
</PrivateMessengerUI:MyUserData>
</ContextMenu>
And use it where you defined your context menu:
ContextMenu="{StaticResource MyAwesomeContextMenu}"
Hope this helps a bit!

WPF Custom Control - ItemsControl template not being applied

I'm building a custom WPF control that derives from TabControl. In the ControlTemplate, I'm using a ItemsControl to display a list that is being bound from the template (an observable collection of type FileMenuItem). During program execution, I'm getting the following error in the output window:
ItemTemplate and ItemTemplateSelector
are ignored for items already of the
ItemsControl's container type;
Type='FileMenuItem'
The type FileMenuItem is derived from MenuItem. If I change the base class to DependencyObject, the code actually runs and the template is applied (so that's an option). I googled the error and couldn't find anything about it, has anyone run into this while developing custom controls? Even though I have a workaround, I'd like to understand what's happening, and I think using the MenuItem as a base class is a cleaner implementation.
I can post more code if it would help. Thanks!

The purpose of a DataTemplate (like ItemTemplate) is to provide a visualization for a data object. Specifically, it defines a set of elements to add to the visual tree in place of the data given to an ContentPresenter or ItemsPresenter. In your case your source list is a collection of objects that are already able to be added directly to the visual tree for display in the UI.
You can see this in the following simplified example where only "Three" shows up in Red because the first two items are defined in a form that can be displayed directly by ComboBox.
<ComboBox>
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding}" Foreground="Red"/>
</DataTemplate>
</ComboBox.ItemTemplate>
<ComboBoxItem>One</ComboBoxItem>
<ComboBoxItem>Two</ComboBoxItem>
<sys:String>Three</sys:String>
</ComboBox>