I have a WPF application and want to share data between my MainWindow and one or more UserConrols, but for simplicity lets assume I have only one MainWindow.xaml and one UserControl.xaml. From what I've gathered so far, this can be done with Bindings and Properties. So I tried this with no success.
The Object I want to share between the controls looks like this:
SharedObject {
prop string Name;
prop List<Product> Products;
}
Product {
prop string ItemName;
prop double Price;
prop bool Available;
}
So I load the SharedData in the MainWindow and want to be able to edit this in the UserControl, but in TwoWay mode, to get the modified product list updates also in the MainWindow. I also want to access and modify the Name Property of the SharedObject in the UserControl.
How can I achieve this? Is the Property/Binding the way to go? Can this state management also be done in a more elegant way? (in dotnet Core 3.1)
You should set the DataContext of the window to an instance of your view model (SharedObject) and then let the UserControl inherit the DataContext from its parent window (which it does by default).
You can then bind directly to any public property of the view model from the an element in UserControl.
Related
My first question here on the Stack. Forgive me for the bad explanation in advance.
I am working on my first MVVM application (Silverlight). I have a custom user control that contains a ListBox to show navigation items. This control is placed in my main xaml page. I don't know if I need to create a composite view model (my main page view model) with a view model especially for the custom control in it or if there is some way to elevate the ListBox properties that I need to bind to.
Through XAML I don't know how to bind, let's say, the ItemsSource property of the ListBox inside the custom control to my main page viewmodel. Basically, I'm at the point that I am questioning my design decision for trying to bind the custom control through my main page view model.
What I have done so far is create dependency properties for the custom control and try to tunnel those dependency properties down to the ListBox properties. I've achieved success with this method for ItemsSource but am having issues with SelectedItem.
Even if I do get SelectedItem to work, it still feels Wrong. Thanks for any advice in advance.
The UserControl should inherit the DataContext from its parent control, unless you are setting it directly. You can then bind to the properties on your view model from your UserControl.
If you would like to create a ViewModel specifically for the UserControl, you can also do that. You would then expose it as a property on your main ViewModel, and bind to it in the MainPage. Example:
public class MainViewModel
{
public ChildViewModel ChildInfo { get; private set; }
}
And then in the view:
<Grid>
...
<lcl:ChildView DataContext="{Binding ChildInfo}" />
...
</Grid>
Your ChildViewModel would then contain properties like SelectedItem to bind your ListBox to.
i have an object based on ContentControl type and I want to embed custom controls into its content. below is the code.
the problem is that i need MyContainer to have a list of MyControl objects so that it can communicate to them, and each MyControl will need a reference to its MyContainer.
how is this done properly? one way that i see is to declare an attached property on MyControl and set it to the name of the MyContainer object, but this seems redundant because MyCOntrol objects can search the visual tree to find the container. if searching is the right way to do this, where would i place the code that does the search? in MyControl constructor?
thanks for any input
konstantin
public class MyContainer : ContentControl
{
...
}
public class MyConrol : Control
{
...
}
<c:MyContainer>
<Grid>
<c:MyControl />
</Grid>
</c:MyContainer>
You can add property MyControls to MyContainer class, create a template for MyContainer with a list in it (ItemsControl, ListBox or some other list control), put the list itself inside the grid from your sample code, bind the list's ItemsSource to MyControls property.
To get container for the control in XAML, you can use binding with RelativeSource set to FindAncestor.
If you need to find container from code, you should probably do it every time or cache the value on the first use (can controls be moved to another container?). Contructor is not the appropriate place, because first control is created and only then it is put into the tree.
Attached properties are definitely unnecessary.
My understanding is that Silverlight does not support DataTemplates with a DataType attribute.
How then would you accomplish the following in SL (author is Josh Smith, full link below). In a nutshell, he's saying that if you bind a TabControl's tab pages to a collection of ViewModels, WPF will figure out how to display each one on the fly by looking for a DataTemplate that has the appropriate (matching) DataType set. Way cool, but I'm wondering how you would (could?) do this in Silverlight.
Applying a View to a ViewModel
MainWindowViewModel indirectly adds
and removes WorkspaceViewModel
objects to and from the main window's
TabControl. By relying on data
binding, the Content property of a
TabItem receives a
ViewModelBase-derived object to
display. ViewModelBase is not a UI
element, so it has no inherent support
for rendering itself. By default, in
WPF a non-visual object is rendered by
displaying the results of a call to
its ToString method in a TextBlock.
That clearly is not what you need,
unless your users have a burning
desire to see the type name of our
ViewModel classes!
You can easily tell WPF how to render
a ViewModel object by using typed
DataTemplates. A typed DataTemplate
does not have an x:Key value assigned
to it, but it does have its DataType
property set to an instance of the
Type class. If WPF tries to render one
of your ViewModel objects, it will
check to see if the resource system
has a typed DataTemplate in scope
whose DataType is the same as (or a
base class of) the type of your
ViewModel object. If it finds one, it
uses that template to render the
ViewModel object referenced by the tab
item's Content property.
The MainWindowResources.xaml file has
a ResourceDictionary. That dictionary
is added to the main window's resource
hierarchy, which means that the
resources it contains are in the
window's resource scope. When a tab
item's content is set to a ViewModel
object, a typed DataTemplate from this
dictionary supplies a view (that is, a
user control) to render it, as shown
in Figure 10.in Figure 10.
http://msdn.microsoft.com/en-us/magazine/dd419663.aspx in Figure 10.
Here is ONE way you can do it. I have used a technique like this in the past, and had great success with it.
Consider a very simple container that will create the view for you like this:
public class ViewMapper : ContentControl
{
protected override void OnPropertyChanged(DependencyPropertyChangedEventArgs e)
{
base.OnPropertyChanged(e);
if (e.Property.Name == "DataContext")
WhenDataContextChanges();
}
private void WhenDataContextChanges()
{
if (DataContext == null)
Content = null;
else
Content = ViewFactory.GetView(DataContext.GetType());
}
}
EDIT
So, you can use this control to do the mapping for you:
<Border DataContext="{Binding MyViewModel}">
<ViewMapper />
</Border>
END EDIT
Note that ViewMapper simply waits for the data context to change, looks up the appropriate view for the data type, and creates a new one. It relies on ViewFactory, which is a very simple static lookup that maps types to views:
public class ViewFactory
{
private static readonly Dictionary<string, Func<UIElement>> _registry = new Dictionary<string, Func<UIElement>>();
private static string Key(Type viewModelType)
{
return viewModelType.FullName;
}
public static void RegisterView(Type viewModelType, Func<UIElement> createView)
{
_registry.Add(Key(viewModelType), createView);
}
public static UIElement GetView(Type viewModelType)
{
var key = Key(viewModelType);
if (!_registry.ContainsKey(key))
return null;
return _registry[key]();
}
}
Then, you simply need to register the view mappings some place:
ViewFactory.RegisterView(typeof(SomeViewModel), () => new SomeView());
Note that ViewFactory could just as easily use Activator.CreateInstance instead of using the Func mechanism. Take that one step further, and you can use an IoC container... You could always decide to map via a string Name property on the ViewModel instead of a type... the possibilities are endless and powerful here.
I've created a new WPF project, and threw in a DataGrid. Now I'm trying to figure out the easiest way to bind a collection of data to it.
The example I downloaded seems to do it in the window c'tor:
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
DataContext = new ViewModel();
}
}
But then the bindings don't seem to appear in the Visual Studio's Properties window. I'm pretty sure there's a way to set the data context in XAML too... it would make me even happier if I could do it directly through the properties window, but all the Binding options are empty. What's the typical approach?
Edit: At 14 minutes, he starts to talk about other methods of setting the data context, such as static resources, and some "injection" method. I want to learn more about those!
What I typically do is use MVVM. You can implement a simplified version by setting the data context in your code behind and having a model type class that holds your data.
Example: In your code behind
DataContext = Model; // where Model is an instance of your model
then in your view
<DataGrid .... ItemsSource="{Binding SomeProperty}">....
Where SomeProperty is an enumerable property on your view model
You can also set a data context in XAML by using the DataContext property
<uc:SomeUserControl DataContext="{Binding AnotherProperty}"....
This will run your user control within the DataContext of the AnotherProperty on your model.
Note that this is grosely simplified but it'll get you on your way.
Have a look at the MVVM design pattern. This pattern is very suitable for wpf applications.
There is described where to store your data and how to bind your ui to the data.
I have a UserControl which contains 4 ToggleButtons and I'd like to trigger a custom event that an interested object can listen for which provides a status, based on the ToggleButton Checked values and also value(s) from the DataContext object.
Getting the ToggleButton checked values and deriving a status is simple enough, however I can't work out how I access the DataContext object within the C# codebehind.
For example, if an interested object receives the RoutedEvent from the UserControl, I would like it to be able to access values from the UserControl's DataContext object.
Will I need to expose specific properties from the DataContext object or can I somehow expose the DataContext object from the UserControl's API?
Update.
To explain the problem a little more, I have a list of items which creates a set of UserControl instances in a container, I attach event listeners to each item as it's added to the container and send an event from one of the UserControls when it's child controls are clicked / checked etc.
Getting a reference to the UserControl that dispatched the event is straightforward enough, but I can't access the DataContext object, do I need to assign a public property to expose the DataContext object ...
e.g.
private ControlViewModel myControlViewModel;
public ControlViewModel MyControlViewModel {
get { return myControlViewModel; }
set
{
this.DataContext = value;
myControlViewModel = value;
}
}
or is there a better way?
Any tips would be appreciated, Thank you.
Well, it looks like I should've tried the simplest solution first...
...of course I can access the DataContext object like this:
(userControl.DataContext as ControlViewModel).requiredProperty;
Update
So I ended up passing the DataContext view model reference via a event/delegate pair like this...
public delegate void StatusChangedHandler(string status, UserControlViewModel model);
public event StatusChangedHandler StatusChanged;
And then just invoked the event like this...
StatusChanged.Invoke("message", DataContext as UserControlViewModel)
// or DataContext as IUserControlModelInterface
Which allowed me to adequately aggregate events from the UserContol's child controls, and access the DataContext model from an event handler.
I still wonder if there is a more best practice way to do this?