Question
Basically I would like to do the following but it seems that I cannot:
UserControl myControl = new UserControl();
DataTemplate template = new DataTemplate(myControl);
The question: Is it possible to construct a DataTemplate from UserControl instance? If not, are there any other possible solutions?
Real problem
I'm working on a project where majority of UI views are simple static Word-like documents (e.g some text fields and maybe some images, nothing too fancy). Because most of persons working on this project are not coders we have designed very simple in-house markup language for UI generation. An example of markup of simple view is following:
First name: [Person.FirstName]
Last name: [Person.LastName]
Address: [Person.Address.Street], [Person.Address.City]
Now these templates are loaded at runtime and usercontrols are created based on them. In this case one usercontrol would be created and it would contain simply couple of stack panels and text blocks so that resulting control would look a bit like text document. XAML equivalent would be something like:
<StackPanel>
<StackPanel Orientation="Horizontal">
<TextBlock Text="First name: "/>
<TextBlock Text={Binding Person.FirstName}
</StackPanel>
<StackPanel>
...
</StackPanel>
...
</StackPanel>
Then, I started to implement support for lists but couldn't think of a way how to do that. In theory it is simple and I came up with following syntax (+ XAML equivalent):
[List Customers]
First name: [Person.FirstName]
Last name: [Person.LastName]
Address: [Person.Address.Street], [Person.Address.City]
[EndList]
->
<StackPanel>
<ItemsControl ItemsSource="{Binding Customers}">
<ItemsControl.ItemTemplate>
<DataTemplate>
[Insert code from previous XAML example here]
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</StackPanel>
But I can't do that because it seems that I cannot construct DataTemplate directly from UserControl instance. There would be no problems if my UserControls were types, but they are not.
One possible solution is that I could bind ItemsControl.Items directly to list of UserControls (instead of binding to ItemsSource and ItemTemplate) but this is sub-optimal in our case for couple of reasons. I would be willing to try some other solutions first!
Update
For clarification: all I have is plain instance of UserControl class which contains the content I need. E.g.
UserControl control = new UserControl();
var panel = new StackPanel();
panel.Children.Add(...);
panel.Children.Add(...);
control.Content = panel;
// How to use that control as ItemTemplate for ItemsControl?
// It seems that it is not possible directly but I want to
// know what my options are.
I don't have class for it because I'm constructing it at run-time and I don't want to create new type dynamically by emiting IL code because it is way too painful.
Creating a datatemplate from Code behind goes like this:
FrameworkElementFactory factory = new FrameworkElementFactory(MyUserControl.GetType());
DataTemplate dt = new DataTemplate();
dt.VisualTree = factory;
yourItemsControlInstance.ItemTemplate = dt;
A datatemplate is a definition of controls to be built at runtime, that is way this construction with a ElementFactory. You do not want the same instance of the UserControl for every item in your ItemsControl.
Ah I understand your problem now. I don't think there is an easy way (one or two lines of code) to create a datatemplate from a UserControl instance.
But to solve your problem I see two directions:
At the point where an usercontrol is created, create a datatemplate instead and use that. It will be cumbersome, with nested FrameworkElementFactories. I have never done that, and the MSDN documentation says that you may encounter some limitations you cannnot do compared to datatemplates in Xaml. But if it is simple it must be doable. There used to be a codeproject article by Sacha Barber you could use as a guidance (if needed).
You pack the creation of the UserControl in a method called private UserControl createMyUserControl(){}
And do something like this:
ItemsControl itemsControl = new ItemsControl();
foreach (var customer in Customers)
{
var usercontrol = createMyUserControl(...);
usercontrol.DataContext = customer;
itemsControl.Items.Add(usercontrol);
}
Second option is less elegant in my opinion, so I would check out the option 1 first.
WPF: How to create Styles in code/and magical Content (see section at the end for extensive sample of a DataTemplate in Code behind)
I think you can replace UserControl with the ContentControl.
Just set the content of the ContentControl to the desired template and use it as ItemTemplate for the ItemsControl.
Related
I'm trying to set a new DataTemplate as a new Window resource in my MainWindow derived from the System.Windows.Window class. The code for the XAML is quite simple and looks like this:
<Window.Resources>
<DataTemplate DataType="{x:Type model:MyViewModel}">
<view:MyView />
</DataTemplate>
</Window.Resources>
What I exactly do here?
I try to show my data (MyViewModel) in or as a specific view (MyView). So far I do understand. Otherwise I wouldn't see the form itself, but the view model as a string with my.namespace.MyViewModel in the window.
But programmatically I do not understand, how to achieve the same. I know, that I have to add a new DataTemplate to the resources of my window. For this I have to "tell" the DataTemplate, which view to use (for the representation) and which data I want to represent, right?
So it must be something with:
DataTemplate template = new DataTemplate();
template.DataType = typeof(MyViewModel);
// Something, something ...
this.Resources.add(...);
Is this the right way to go? Or am I completely wrong?
I searched the web for solutions and also my WPF book, but there are only XAML implementations.
Why do I do that?
I have a headered content control which loads view models dynamically. The problem here is, that the user controls are sometimes dynamic and in case of data presentation I need to assign a specific (dynamic created) view to the data. So I try to load the current static user controls also in the way shown above.
Is there a way to go?
Or is there a better way to achieve the same results?
I want to create a template (resource dictionary) for my app. where my type inherits the button type and I then can call it through:
<my-custom-type inherit from button>
</my-custom-type inherit from button>
And of course in WPF.
More specifically, I would like to create copies of the control in the image below with simple XAML syntax as above.
There are two approaches to this, each with their own pros and cons:
Templates allow you to reuse a section of XAML. There is (almost always) no code-behind, and you certainly won't be deriving from Button. For example, if you wanted to have a bordered text box repeated in an ItemsControl:
<DataTemplate x:Key="MyDataTemplate">
<Border>
<TextBox/>
</Border>
</DataTemplate>
Or in a button class you use ContentTemplate:
<Button ContentTemplate={StaticResource MyTemplate}>
</Button>
And you would use it as XTemplate="{StaticResource MyDataTemplate}" in an existing control that used templates. This is usually the way to go. Note that the name of the property won't be Template, but ItemTemplate, or ContentTemplate or something similar.
The exception is if you want custom behavior, in which case you use a UserControl. This technically could inherit from Button though you usually wouldn't. Subclassing a basic control should only be done if you are sure you actually want to do that. Once your user control is created, the syntax would look similar to what you have in your question:
<local:MyButton>
</local:MyButton>
Note that "local" is a made-up xmlns. Your user control would consist of whatever controls you wanted, and you can expose "attributes" to the using code via dependency properties.
seems like a trivial task: i am building a wpf application, using MVVM pattern. what i want is dynamically change part of a view, using different UserControls, dependent on user input.
let's say, i have got 2 UserControls, one with a button, and another with a label.
in main view i have a container for that. following XAML "works":
<GroupBox Header="container" >
<local:UserControlButton />
</GroupBox>
and a UserControl element with buttons pops up. if i change it to another one, it works too.
question is how to feed that groupbox dynamically. if i put something like that in my model view:
private UserControl _myControl;
public UserControl MyControl
{
get
{
return _myControl;
}
set
{
_myControl= value;
InvokePropertyChanged("MyControl");
}
}
and change my view XAML to something like:
<GroupBox Header="container" >
<ItemsControl ItemsSource="{Binding MyControl}" />
</GroupBox>
and feed it from command with usercontrol for button or for label: nothing happens, although "MyControl" variable is set and is "invoke property changed"..
Obviously there are many ways to skin this particular cat - but to answer the question of why it doesn't work you need to look into the ItemsSource property of ItemsControl on MSDN.
The items control is designed to show multiple items, provided through an IEnumerable passed to the ItemsSource property. You are passing a UserControl, so the binding will fail.
For your example, I would change the ItemsControl to a ContentControl and bind the content to your MyControl property. This should then work.
<GroupBox Header="container" >
<ContentControl Content="{Binding MyControl}" />
</GroupBox>
However, I would strongly recommend looking into other ways of doing this - having a control in your VM breaks MVVM to my mind. Depending on what you are doing look at data templates - #Sheridan's link in the comments provides an great description of a way to do it.
Couldn't post this as a comment so adding as answer..
Have a look at this:
Implementing an own "Factory" for reusing Views in WPF
It uses DataTemplates but doesn't require the DataTemplate section for each view. If you potentially have a lot of user controls/views you wish to display or you are reusing through multiple views or you are intending to actually dynamically generate a view (versus just loading an existing user control) then this might suite your needs.
I have a UserControl named "WorkspaceView" and its only purpose is to show other views as tabs. Call these views ViewA, ViewB etc. Which of these views to present should be determined on runtime, so I figured I needed a control that can present ... well ..stuff.
ContentControl to the rescue. Except ... I can't make it work. I'm trying to new up a usercontrol of type ViewA in the code behind and assign it to my MyContent, which is the ContentControl. I've tried:
public WorkspaceView()
{
InitializeComponent();
DataContext = new View(A); //Hoping that the DataContext will propagate down
}
Second attempt was
public WorkspaceView()
{
InitializeComponent();
var binding = new Binding {Source = new ViewA()};
MyContent.SetBinding(ContentControl.ContentProperty, binding);
}
In both cases, I see an empty box, but since I've hard wired a TextBlock into ViewA, I'd expect it to show me that text. What am I doing wrong?
Despite knowing that MVVM is the preferred way to develop WPF applications, I'd prefer to see how I can do this with code behind files. Later on, I will redo the application with MVVM, but first I need to get some basic understanding of WPF.
In response to the suggestions so far, I've tried
MyContent.Content = new ViewA();
but still I the text that is in ViewA does not appear. I've also at the bottom of this post included a screenshot of what the application renders.
WorkspaceView
Resource file
What is rendered
Have you tried simply doing this?
MyContent.Content = new ViewA();
EDIT
Try simplifying your code a bit and working from there. For instance:
public WorkspaceView()
{
InitializeComponent();
// Something better than UserControl should be used here
ObservableCollection<UserControl> views = new ObservableCollection<UserControl>();
views.Add(new ViewA());
views.Add(new ViewB());
DataContext = views;
}
<Border ..>
<TabControl x:Name="TabControl"
..
ItemsSource="{Binding}" />
</Border>
This code sets a WorkspaceView.DataContext to a collection of UserControls. When you specify {Binding} whithin WorkspaceView's XAML you are refering to the whole DataContext object (i.e. your collection.) This way you are setting the TabControl.ItemsSource to your collection of views.
Now you could create DataTemplates targeting the type of each view to control how each control is displayed in its tab within the TabControl.
I have defined the DataTemplate in the XAML, however I need to change it to be defined at run time, because its binding is dynamic.
<UserControl.Resources>
<DataTemplate x:Key="myCellTemplate">
<TextBlock Text="{Binding Description}" Margin="4"/>
</DataTemplate>
</UserControl.Resources>
Is there any way to define it in code-behind?
Thank you.
You might be able to accomplish what you need with a custom DataTemplateSelector and I'd recommend that approach, if possible. That said, it is possible to create a DataTemplate in code:
Type type = typeof(MyUserControl); //for example
var template = new DataTemplate();
template.VisualTree = new FrameworkElementFactory(type);
return template;
In this context, type is the type of visual element you want to have as the root of your template. If necessary, you could add additional elements using the factory, but in the one case where I've used this, I simply created UserControl elements to represent the different templates I was dynamically creating.
My apologies, this apparently isn't supported in Silverlight. In Silverlight, you have to use XamlReader.