Purely for code and template simplification I want to be able to have each item inside my items control bound to a property inside each array element. For example
public List<MyObject> MyObjectList; //If I bind to this, each item recieves MyObject as its data context.
I want the ability for each item to recieve MyObject.SomeProperty as its data context. I thought through setting ItemContainerStyle I could set the datacontext but that doesn't appear to work. Does anybody have any ideas?
Somthing along the lines of the following, so each Item is bound to the Property "FieldValue" inside of each object. But in this case, it grabs the "FieldValue" binding from the root object, not each individual item.
<ItemsControl ItemsSource="{Binding MyArrayOfObjects, ItemTemplateSelector="{StaticResource MyObjectTemplateSelector}">
<ItemsControl.ItemContainerStyle>
<Style>
<Setter Property="Control.DataContext" Value="{Binding FieldValue}"/>
</Style>
</ItemsControl.ItemContainerStyle>
</ItemsControl>
Thanks in advance.
Related
To familiarize myself with WPF and MVVM concepts I built a visual representation of a Sudoku board.
My (simplified) setup looks like this (no custom code-behind in views anywhere):
I have a MainWindow.xaml:
<Window x:Class="Sudoku.WPF.MainWindow">
<Window.DataContext>
<models:MainWindowViewModel/>
</Window.DataContext>
<ctrl:SudokuBoard DataContext="{Binding Path=GameViewModel}"/>
</Window>
My MainWindowViewModel:
class MainWindowViewModel
{
public MainWindowViewModel()
{
IGame g = new Game(4);
this.GameViewModel = new GameViewModel(g);
}
public IGameViewModel GameViewModel { get; private set; }
}
SudokuBoard is a UserControl. Its DataContext is set to GameViewModel as per above.
Relevant parts of GameViewModel, Elements is populated in the ctor, Possibilities is set via a command:
public IList<CellViewModel> Elements { get; private set; }
private bool _showPossibilities;
public bool ShowPossibilities
{
get { return _showPossibilities; }
set
{
_showPossibilities = value;
OnPropertyChanged();
}
}
In SudokuBoard.xaml I have:
<ItemsControl x:Name="SudokuGrid" ItemsSource="{Binding Path=Elements}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<UniformGrid/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<ContentControl Style="{StaticResource ToggleContentStyle}"
Content="{Binding}" />
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
Elements is a collection of CellViewModels generated in the constructor of GameViewModel.
Now to the question: my ToggleContentStyle as defined in <UserControl.Resources>:
<Style x:Key="ToggleContentStyle" TargetType="{x:Type ContentControl}">
<Style.Triggers>
<DataTrigger Binding="{Binding Path=DataContext.ShowPossibilities, ElementName=SudokuGrid}" Value="False">
<Setter Property="ContentTemplate" Value="{StaticResource valueTemplate}"/>
</DataTrigger>
<DataTrigger Binding="{Binding Path=DataContext.ShowPossibilities, ElementName=SudokuGrid}" Value="True">
<Setter Property="ContentTemplate" Value="{StaticResource possibilityTemplate}" />
</DataTrigger>
</Style.Triggers>
</Style>
(both ContentTemplates just show other properties of a single CellViewModel in different representations)
Question 1: I have to explicitly reference DataContext in order to get to the ShowPossibilities property. If I leave it out, so that Path=ShowPossibilities, I get a UniformGrid with the ToString() representation of CellViewModel. My assumption is that that is because the style is referenced from the ItemTemplate, with it's binding set to a single CellViewModel. Is that assumption valid?
Question 2: When I omit the ElementName part, I also get the ToString() representation of CellViewModel. Now I'm really confused. Why is it needed?
Datacontext is a dependency property which is marked as inherits. That means its inherited down the visual tree.
When you bind the default place it's going to look for a source is in the datacontext.
This is the simple situation.
Say you have a window and that has datacontext set to WindowViewmodel and stick a textbox in that Window. You bind it's Text to FooText. This means the textbox goes and looks for a FooText property in that instance of WindowViewmodel.
All pretty simple so far.
Next...
You use elementname.
What that does is says go and take a look at this element. Look for a property on that. If you did that with our textbox above then it would expect a dependency property FooText on whatever you point it to.
Datacontext is a dependency property.
And when you do:
"{Binding FooProperty
This is shorthand for:
"{Binding Path=FooProperty
Where FooProperty is a property path, not =just the name of a property.
Which is maybe worth googling but means you can use "dot notation" to walk down the object graph and grab a property on an object ( on an object.... ).
Hence DataContext.Foo or Tag.Whatever ( since tag is another dependency property a control will have ).
Let's move on to some other complications.
The datcontext is inherited down the visual tree but there's a few of gotchas here. Since
some things look like they're controls but are not ( like datagridtextcolumn ). Templated things can be tricky. Itemscontrols are a kind of obvious and relevent special case.
For an itemscontrol, the datacontext of anything in each row is whichever item it's presented to from the itemssource. Usually you're binding an observablecollection of rowviewmodel to that itemssource. Hence ( kind of obviously ) a listbox or datagrid shows you the data from each rowviewmodel you gave it in each row.
If you then want to go get a property is not in that rowviewmodel you need to tell it to look somewhere else.
When you specify an element in Binding (eg ElementName=SudokuGrid), the Path has to refer to any property of that element. Because this element is a wpf control, DataContext is one of it's properties but ShowPossibilities isn't. So if you do just Path=ShowPossibilities it will not be able to find that path at all.
If you don't specify element in Binding at all then it defaults to the DataContext associated with the control. If the associated DataContext doesn't have the property ShowPossibilities it will not be able to find it.
PS: If you want to debug wpf UI to see what the DataContext is at run-time you could use utility like Snoop.
I am trying to get the bool value of the checkbox present in the Listview. I am binding to a bool public property "Assignm" in the view model. I tried the below binding pattern but the problem is if i select one checkbox it selects all checkboxes and vice versa. I think this is because relativesource is listview and it works on complete listview. I also tried changing the relative source to ListviewItem but that didn't trigger anything. Can someone help me please. Do i need to change something here ?
<GridViewColumn.CellTemplate>
<DataTemplate>
<CheckBox Tag="{Binding MU_Identifier}" IsChecked="{Binding DataContext.Assignm, RelativeSource={RelativeSource FindAncestor, AncestorType=ListView}}">
</CheckBox>
</DataTemplate>
</GridViewColumn.CellTemplate>
Because your binding for IsChecked property is Assignm property which seems to be one property of your view model.
If there is a boolean property named Assignm for the data model of the DataSource of ListView, then just change the binding like this: {Binding Assignm}, as Tag property does.
All your items are bounded to a single property, so when one item changes a property in your context it changes on other items.
To provide correct work all your items from ItemsSource should have property IsChecked.
Check this Example
I have a WPF data grid with multi select (SelectedMode = Extended). Each item has an IsSelected binding per https://stackoverflow.com/a/2615487/284795
<DataGrid
ItemsSource="{Binding Items}"
SelectionUnit="FullRow"
SelectionMode="Extended"
SelectedIndex="{Binding SelectedIndex}"
SelectedItem="{Binding SelectedItem}">
<DataGrid.RowStyle>
<Style TargetType="DataGridRow">
<Setter Property="IsSelected" Value="{Binding IsSelected}" />
</Style>
</DataGrid.RowStyle>
</DataGrid>
I'm curious. How do the properties SelectedIndex and SelectedItem on the DataGrid now behave? If two items are selected in the data grid, which one does SelectedItem point to?
Also, if all these bindings are two way, and I make a change to one from a view model, will the others be updated? (I'm observing a bug in my app perhaps because of this)
I had the same question a while ago, and I checked: I created a DataGrid with several items and set the SelectedMode = Extended, and I mde a binding to both: SelectedItem and SelectedIndex properties.
The result was this: When you select a single item, and then you select other items and make a multiselect, the SelectedItem and SelectedIndex properties will be the first item that you selected. So when you make multiselects the selected item will be the first one you selected.
Also all other selected items will be in the SelectedItems collection, that is read only (like in the question you pointed said) and it is not a dependency property, so you can't make bindings to it. So if you want take all selected items, you need to handle the selection changed event of the DataGrid and then, manually, add and remove the new and old items from the collection that you want to keep (selected items).
Hope my answer be clear enough, and it could helps you...
I have a list of tab items that have views dynamically added to them. Every time a user adds a view, a new tab item is created. I'm now trying to bind a menu to a tabcontrol's items so that a user can select from a menu which view is currently the active view.
My menu is bound as such:
<Menu Background="Transparent">
<MenuItem Style="{StaticResource TabMenuButtonStyle}" ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type TabControl}}, Path=Items}" ItemContainerStyle="{StaticResource TabMenuItem}"></MenuItem>
</Menu>
This works fine and has the desired effect (each menu item is a listing of all the open tabs).
I have the following style that binds menu items to the IsSelected property of the tab items:
<Setter Property="IsChecked" Value="{Binding Path=IsSelected, Mode=TwoWay}" />
My problem is, this binding doesn't work. The binding error message is stating that it can't find the IsSelected property on the view object. I don't want it to use the specfic view, rather, I want it to look at the tab item that the view is currently bound to.
I've tried the following, but still get a binding error:
<Setter Property="IsChecked" Value="{Binding Path=IsSelected, Mode=TwoWay, RelativeSource={RelativeSource AncestorType=TabItem}}}" />
Which states that it can't find an ancestor of type TabItem for each menu item (which makes sense as the menu item's ancestors are not what it is bound to.)
Is there any way I can get access to the parent of the item that is coming in as a binding so I can bind to its properties?
Update:
Per Yadyn's advice, I decided to create a value converter and return tab items.
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
ItemCollection ic = (ItemCollection)value;
List<TabItem> tabItems = new List<TabItem>();
foreach (var obj in ic) {
tabItems.Add((TabItem)obj);
}
return tabItems;
}
This makes binding IsSelected to IsChecked work for static items (TabControls that have their tab items already created), but for the dynamically added views, the Convert method never gets called. It's like the TabControl is not sending out an update to binders of its items that something has changed. Here is how the MenuItem is wired up now:
<MenuItem Style="{StaticResource TabMenuButtonStyle}" ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type TabControl}}, Path=Items, Mode=OneWay, NotifyOnSourceUpdated=True, Converter={StaticResource TabControlItemConverter}}" ItemContainerStyle="{StaticResource TabMenuItem}"></MenuItem>
TabControl.Items will get you back the views, since that is what you've bound to your TabControl to have dynamic tab views.
Unfortunately, there isn't a property you can bind to on the TabControl directly that will get you a collection of the TabItems. These are actually the ItemContainers for each item in the Items bound collection.
What you might do is create a converter or something. You can try using myTabControl.ItemContainerGenerator.ContainerFromItem and pass in the view object to get back the actual TabItem that wraps it. Then your IsSelected binding will work.
You might consider binding directly to the TabControl itself instead of the Items property. Then the converter can easily do the above call to ContainerFromItem. You'll then have to return a List<TabItems> from the converter by enumerating the Items property yourself (calling ContainerFromItem for each).
Anyway, hopefully this gets you on the right track!
Here is something simpler. Define a toplevel viewmodel that holds a collection of viewmodels representing the tabs and menuitems like so
//Not showing here the details of implementing INPC
public class MyCustomCompositeViewModel:INotifyPropertyChanged
{
public ObservableCollection<CompositeViewItem>CompositeItems{get;set;}
public CompositeViewItem SelectedItem{get;set;}
}
On the view, bind the tabitems to the CompositeItems collection and bind the selected tab item to the selectedItem. You can bind the MenuItems similarly
The compositeviewitem should provide properties like the name of the item (for display on the tab and menu), and perhaps the additional data the View needs for rendering. Hope this makes sense.
The subject line says it all really! I have a user control which can be bound successfully to, say, a Fullname object - i.e. it works ok.
I now need to show a list of these and, again, this works ok when the control is in a DataTemplate within ItemsControl.Template.
But, the control has a property (InEditMode) that is not a property of the Fullname object but of the object that has the FullnameList property to which the ItemsControl is bound, via ItemsSource. This InEditMode property works fine when the control is not in a list and is bound to parent sibling properties named, say, ParentInEditMode and ParentFullname.
The question is - what style of binding expression is required to 'get at' the edit mode property of the parent object when the control is an ItemsControl?
Or, should I re-design the Fullname object to contain an EditMode property?
Many thanks in advance!
Update:
The item (i.e. that which is in collection bound to the ItemsControl) does NOT have such a property. Code is very simple:
<ItemsControl ItemsSource="{Binding Path=FullnameList}">
...then...
<ItemsControl.ItemTemplate>
<DataTemplate>
<jasControls:NameView
NameValue="{Binding Path=.}"
InEditMode= ??????? />
The overall parent (the viewmodel for the window) has properties:
FullnameList
ParentInEditMode
Fullname (single item for testing NameView which works perfectly with this xaml outside of any list control using:
<jasControls:NameView NameValue="{Binding Path=Fullname}" InEditMode="{Binding Path=ParentInEditMode}"/>
I would like to apply the edit mode to the entire collection - making that flag part of Fullname does not seem right!?
I have found an answer to my own question, which I hope will help others.
The working syntax I have is this:
<StackPanel>
<ItemsControl ItemsSource="{Binding Path=FullnameList}">
...then...
<ItemsControl.ItemTemplate>
<DataTemplate>
<jasControls:NameView
NameValue="{Binding Path=.}"
InEditMode= "{Binding DataContext.ParentInEditMode,RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type StackPanel}}}" />
This correctly picks up the property that is a sibling of FullnameList and passes it to the data template item. More by luck than judgement, but I hope this is a valid way to do this!
For each Item in ItemsSource, ItemsControl creates the specified DataTemplate and to its DataContext it assigns the respective Item. Now every DataTemplate can bind to its item in its data context.
So I suppose your item does have a property "ParentInEditMode"; there should be no issue with binding to that property.
If it doesn't work, please update your question with some code.