I am trying to bind a property of my DataContext to the SelectedItem on a ComboBox like this:
<ComboBox x:Name="ElementSelector"
ItemsSource="{Binding Source={StaticResource Elements}}"
DisplayMemberPath="ElementName"
SelectedItem="{Binding ValueElement, Mode=TwoWay}">
where the Elements resource is a CollectionViewSource (don't know, whether this matters).
When everything is initialized, the property ValueElement of the DataContext is set to the first item in the CollectionViewSource. What I want, is to initialize it the other way around: I would like to set SelectedItem of the ComboBox to the value of the property or null if no matching item is contained.
How can this be done?
EDIT - Additional information:
The ComboBox is part of a DataTemplate:
<DataTemplate x:Key="ReferenceTemplate"
DataType="viewModels:ElementMetaReferenceViewModel">
<StackPanel Orientation="Horizontal">
<StackPanel.Resources>
<ResourceDictionary>
<views:ElementsForReferenceViewSource x:Key="Elements"
Source="{Binding DataContext.CurrentProject.Elements, ElementName=Root}"
ReferenceToFilterFor="{Binding}"/>
</ResourceDictionary>
</StackPanel.Resources>
<TextBlock Text="{Binding PropertyName}"/>
<ComboBox x:Name="ElementSelector"
ItemsSource="{Binding Source={StaticResource Elements}}"
DisplayMemberPath="ElementName"
SelectedItem=""{Binding ValueElement, Mode=TwoWay}" />
</StackPanel>
</DataTemplate>
The ElementsForReferenceViewSource simply derives from CollectionViewSource and implements an additional DependencyProperty which is used for filtering.
The DataContext of the items in the CollectionViewSource look like this:
public class ElementMetaReferenceViewModel : ViewModelBase<ElementMetaReference, ElementMetaReferenceContext>
{
...
private ElementMetaViewModel _valueElement;
public ElementMetaViewModel ValueElement
{
get { return _valueElement; }
set
{
if (value == null) return;
_valueElement = value;
Model.TargetElement = value.Model;
}
}
...
}
For people encountering the same issue
The above code works as expected. The solution was getting the stuff behind the scenes right. Make sure, that the instance of the ViewModel which is the value of the property you want to bind to is definitely contained in the CollectionViewSource.
In my case the issue was deserializing an object tree incorrectly, so objects were instantiated twice. Then for each object a distinct ViewModel was initialized and then obviously the value of the property was not contained in the list.
Remark
To check whether this is an issue in your case, you can try the following:
Override the ToString() methods of the ViewModels displayed in the ComboBox like this:
public override string ToString()
{
return "VM"+ Model.GetHashCode().ToString();
}
Then you can easily compare the items in the source collection with the value on your property. Not the most professional way, but it did the job for me.
Related
I am working on this problem for about a day now.
For some reason I am unable to TwoWay bind a value to a ComboBox if it is inside a ItemsControl. Outside works just fine.
I have an ObservableCollection of int? in my ViewModel:
private ObservableCollection<int?> _sorterExitsSettings = new ObservableCollection<int?>();
public ObservableCollection<int?> SorterExitsSettings
{
get { return _sorterExitsSettings; }
set
{
if (_sorterExitsSettings != value)
{
_sorterExitsSettings = value;
RaisePropertyChanged("SorterExitsSettings");
}
}
}
My XAML:
<ItemsControl ItemsSource="{Binding SorterExitsSettings}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<ComboBox ItemsSource="{Binding RelativeSource={RelativeSource AncestorType=ItemsControl}, Path=DataContext.ScanRouter.Stores}"
SelectedValue="{Binding Path=., Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" DisplayMemberPath="name" SelectedValuePath="id" IsEditable="True" />
</DataTemplate>
</ItemsControl.ItemTemplate>
So the ComboBox is populated with a list of stores. It works fine so far.
The ObservableCollection SorterExitsSettings even has some values set which are shown in the displayed ComboBoxes. So setting the SelectedValue also works.
However when I change a selection, SorterExitsSettings wont change. While when I implement the ComboBoxes(100) without an ItemsControl it suddenly works fine.
<ComboBox ItemsSource="{Binding ScanRouter.Stores}" DisplayMemberPath="name" SelectedValuePath="id" IsEditable="True" SelectedValue="{Binding SorterExitsSettings[0], Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
Even better when I implement the ComboBoxes using the ItemsControl and also the example ComboBox shown above. When I change the single ComboBox's value it will change the value of the ComboBox inside the ItemsControl, but not the other way around.
Did somebody encounter this problem before?
My guess was that the ItemsControl doesn't like the fact that I am binding my selected value to an item in a list. However when I bind directly to a ViewModel property(Store) it also doesn't work.
I also tried using SelctedItem instead of SelectedValue and populate the ObservableCollection with Store objects instead of int?.
The problem is that you're binding your ComboBox's SelectedValue directly to the collection elements which are type int ?. This won't work, binding targets have to be properties. Try wrapping your int ? values in a class and expose the value as a property of that class with a getter and setter, i.e. something like this:
private ObservableCollection<Wrapper> _sorterExitsSettings = new ObservableCollection<Wrapper>();
... etc...
And:
public class Wrapper
{
public int? Value {get; set;}
}
And finally:
<ComboBox ... SelectedValue="{Binding Path=Value, Mode=TwoWay...
Post back here if you still have problems.
Consider this container:
public class ItemInfo : DependencyObject
{
public string Name { get; set; }
public ObservableCollection<SomeDataItem> DataValues { get; set; }
...
Dependency object registration and event handling
...
}
public class MyItemSource : ObservableCollection<ItemInfo>
{
...
}
Now, I wish to display this data in a listview where the control that displays the item is custom. For that, I'd set the MyItemSource to listview's ItemSource and define a ItemTemplate. However, it seems that I have no access to ItemInfo in the ItemTemplate. This is my XAML:
<Grid>
<ListBox ItemsSource="{StaticResource MyStaticDataSource}"
Grid.IsSharedSizeScope="True">
<ListBox.ItemTemplate>
<DataTemplate>
<local:ItemInfoUserControl x:Name="itemInfoUserControl"
Name = "{Binding Name}" <--- this doesn't work
Data = "{Binding DataValues}" <--- this doesn't work
Width="300" Height="200"
Grid.Row="1">
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</Grid>
Instead of binding to ItemSource's ItemInfo, it binds to the ItemInfoUserControl properties, which is not what I wish it to do. Is there a way to bind properties in itemtemplate to a property in itemsource ? Or is there an alternative approach to what i'm ultimately trying to accomplish ?
Thanks!
Well, first of all you need to use proper binding syntax:
Name = "{Binding Name}"
and
Data = "{Binding DataValues}"
Instead of just "Name = "Binding Name"" and "Data = "Binding DataValues"". Note the addition of "{" and "}" around your binding expression.
This might be enough to solve your problem, as long as Name and DataValues are DependencyProperties in ItemInfoUserControl. If not, you'll need to implement them as DependencyProperties in order to be able to bind to them in XAML. See here for a good MSDN article on defining custom dependency properties.
Edit: Also, just noticed -- you're setting both x:Name and Name. From this article on MSDN:
If Name is available as a property on the class, Name and x:Name can be used interchangeably as attributes, but a parse exception will result if both are specified on the same element. If the XAML is markup compiled, the exception will occur on the markup compile, otherwise it occurs on load.
Remove x:Name="itemInfoUserControl" and see if that helps.
I have a ViewModel (AbstractContextMenu) that represents my context menu (IContextMenu), and I bind a real ContextMenu to it with a DataTemplate:
<DataTemplate DataType="{x:Type local:AbstractContextMenu}">
<ContextMenu x:Name="contextMenu"
ItemsSource="{Binding Path=(local:IContextMenu.Items)}"
IsEnabled="{Binding Path=(local:IContextMenu.IsEnabled)}"/>
</DataTemplate>
Then I have a dummy ConcreteContextMenu for testing that just inherits from AbstractContextMenu. AbstractContextMenu just implements this interface:
public interface IContextMenu : IExtension
{
IEnumerable<IMenuItem> Items { get; set; }
bool IsEnabled { get; set; }
}
I'm using it as a property of another ViewModel object:
public IContextMenu ContextMenu
{
get
{
return m_ContextMenu;
}
protected set
{
if (m_ContextMenu != value)
{
m_ContextMenu = value;
NotifyPropertyChanged(m_ContextMenuArgs);
}
}
}
private IContextMenu m_ContextMenu = new ConcreteContextMenu();
static readonly PropertyChangedEventArgs m_ContextMenuArgs =
NotifyPropertyChangedHelper.CreateArgs<AbstractSolutionItem>(o => o.ContextMenu);
Then I bind a StackPanel to that ViewModel and bind the ContextMenu property on the StackPanel to the ContextMenu property of the ViewModel:
<StackPanel Orientation="Horizontal"
ContextMenu="{Binding Path=(local:AbstractSolutionItem.ContextMenu)}"
ContextMenuOpening="stackPanel_ContextMenuOpening">
<!-- stuff goes in here -->
</StackPanel>
When I run this, the ContextMenuOpening event on the StackPanel is fired, but the ContextMenu is never displayed. I'm not sure if I can even do this (apply a ContextMenu to a ContextMenu ViewModel using a DataTemplate). Anyone know?
What is the type of AbstractSolutionItem.ContextMenu? If it corresponds to the ContextMenu property in your question, then the problem could be that the type is wrong. The ContextMenu property of FrameworkElement is expecting an actual ContextMenu, not an IContextMenu. Try checking the output window while debugging your app - you might get an error message stating that this is the problem.
Instead of using a DataTemplate to define your ContextMenu, just put the contents of the template StackPanel.ContextMenu:
<StackPanel Orientation="Horizontal"
ContextMenu="{Binding Path=(local:AbstractSolutionItem.ContextMenu)}"
ContextMenuOpening="stackPanel_ContextMenuOpening">
<StackPanel.ContextMenu DataContext="{Binding Path=(local:AbstractSolutionItem.ContextMenu)}">
<ContextMenu x:Name="contextMenu"
ItemsSource="{Binding Path=Items}"
IsEnabled="{Binding Path=IsEnabled}"/>
</StackPanel.ContextMenu>
<!-- stuff goes in here -->
</StackPanel>
That should get you most of the way there. However, there is still a problem since the ContextMenu does not know how to create a MenuItem from an IMenuItem. To solve this, create an ItemTemplate for the ContextMenu, which binds members of IMenuItem to `MenuItem.
Could you shed some light on the syntax used in the ItemsSource property in the DataTemplate ? Using parentheses usually means an attached property. And Items does not seem to be an attached property defined by IContextMenu (as an interface cannot define such a property).
The DataTemplate is linked to an object of type AbstractContextMenu which has a property called Items. So, the DataTemplate could simply reference it like this:
<DataTemplate DataType="{x:Type local:AbstractContextMenu}">
<ContextMenu x:Name="contextMenu"
ItemsSource="{Binding Path=Items)}"
IsEnabled="{Binding Path=IsEnabled}"/>
</DataTemplate>
If the AbstractSolutionItem class is the VM of the StackPanel, you could bind it like this:
<StackPanel Orientation="Horizontal"
ContextMenu="{Binding Path=ContextMenu}"
ContextMenuOpening="stackPanel_ContextMenuOpening">
<!-- stuff goes in here -->
</StackPanel>
Of course, the DataTemplate must be "accessible" from the StackPanel.
Bind the ContextMenu property of your view (StackPanel in this scenario) to the ContextMenu property of your ViewModel and provide a IValueConverter to the binding that will create the ContextMenu object and set the IContextMenu to it's DataContext.
In WPF Databinding, I understand that you have DataContext which tells an element what data it is going to bind to and ItemsSource which "does the binding".
But e.g. in this simple example it doesn't seem that ItemsSource is doing anything useful since, what else would you want the Element to do to the DataContext except bind to it?
<ListBox DataContext="{StaticResource customers}"
ItemsSource="{Binding}">
And in more complex examples of ItemsSource, you have Path and Source which seems to be encroaching on the territory of DataContext.
ItemsSource="{Binding Path=TheImages, Source={StaticResource ImageFactoryDS}}"
What is the best way to understand these two concepts as to know when and how to apply each of them in various coding scenarios?
DataContext is just a handy way to pick up a context for bindings for the cases where an explicit source isn't specified. It is inherited, which makes it possible to do this:
<StackPanel DataContext="{StaticResource Data}">
<ListBox ItemsSource="{Binding Customers}"/>
<ListBox ItemsSource="{Binding Orders}"/>
</StackPanel>
Here, Customers and Orders are collections on the resource called "Data". In your case, you could have just done this:
<ListBox ItemsSource="{Binding Source={StaticResource customers}}"/>
since no other control needed the context set.
ItemsSource property will be binded with collection object directly OR collection property of binding object of DataContext property.
Exp:
Class Root
{
public string Name;
public List<ChildRoot> childRoots = new List<ChildRoot>();
}
Class ChildRoot
{
public string childName;
}
There will be two ways to bind ListBox control:
1) Binding with DataContext:
Root r = new Root()
r.Name = "ROOT1";
ChildRoot c1 = new ChildRoot()
c1.childName = "Child1";
r.childRoots.Add(c1);
c1 = new ChildRoot()
c1.childName = "Child2";
r.childRoots.Add(c1);
c1 = new ChildRoot()
c1.childName = "Child3";
r.childRoots.Add(c1);
treeView.DataContext = r;
<TreeViewItem ItemsSource="{Binding Path=childRoots}" Header="{Binding Path=Name}">
<HierarchicalDataTemplate DataType="{x:Type local:Root}" ItemsSource="{Binding Path=childRoots}">
2) Binding with ItemSource:
ItemsSource property takes collection always.
here we have to bind collection of Root
List<Root> lstRoots = new List<Root>();
lstRoots.Add(r);
<HierarchicalDataTemplate DataType="{x:Type local:Root}" ItemsSource="{Binding Path=childRoots}">
In First example we have bind DataContext which has object inside that object we have collection which we binded with ItemSource property where in Second example we have directly bind ItemSource property with collection object.
I've created two UserControls, the first of which displays a list of objects, the second of which displays details about an object that is selected from the first. I've created a dependency property on the first control and am binding each UserControl to an object declared in my Resources collection. I've seen blog posts describing this, but cannot seem to get it to work. I am getting a XamlParseException. The funny thing is the exception only occurs when I set the binding Mode=TwoWay on my first UserControls. Here's the code...
Page.xaml
<UserControl.Resources>
<local:Item x:Key="SelectedItem" />
</UserControl.Resources>
...
<controls:ItemList
SelectedItem="{Binding Mode=TwoWay, Source={StaticResource SelectedItem}}">
</controls:ItemList >
...
<controls:ItemDetails
DataContext="{Binding Source={StaticResource SelectedItem}}">
</controls:ItemDetails>
ItemList.xaml.cs
public partial class ItemList: UserControl
{
public ItemList()
{
InitializeComponent();
}
public static readonly DependencyProperty SelectedItemProperty =
DependencyProperty.Register("SelectedItem", typeof(Item), typeof(ItemList), new PropertyMetadata(new Item()));
public Item SelectedItem
{
get { return (Item )GetValue(SelectedItemProperty ); }
set { SetValue(SelectedItemProperty , value); }
}
Any suggestions are welcome!
Your Xaml is incorrect, from the looks of it. You are missing a property that you need to bind to for two-way. You are saying that you want to bind to object defined in source, but you don't specify a property of that resource to bind to. In this case, the SelectedItem resource is an object of type Item ... you need to bind to property of Item. So if item has a property named value, your Xaml could look like this:
SelectedItem="{Binding Value, Source={StaticResource SelectedItem}, Mode=TwoWay}"
Try this instead:
SelectedItem="{Binding SelectedItem, Mode=TwoWay}"
ib.