I've been going round in circles with this for a couple of days, and I'm hoping a WPF guru can see where I'm going wrong.
I'm setting CurrentViewModel in code. The Selected item of my ListBox and the Content of my ContentControl bind correctly. But when changing the selected item in the Listbox via the UI the CurrentViewModel is being set but the Content Control is not being updated.
I'm using a data template to map my Views and View Models.
<DataTemplate DataType="{x:Type ViewModel:MyViewModel}">
<View:MyView />
</DataTemplate>
I have a ListBox which is bound to an observable collection of ViewModels. The Selected Item is bound to the current view model.
<ListBox ItemsSource="{Binding MyViewModelCollection}" DisplayMemberPath="DisplayName" SelectedItem="{Binding CurrentViewModel, Mode=TwoWay}"/>
I also have a content control that is also bound to the CurrentView Model
<ContentControl Content="{Binding CurrentViewModel, Mode=TwoWay}"/>
This is the property that they are both bound to
public MyViewModel CurrentViewModel
{
get
{
return _currentViewModel;
}
set
{
if (_currentViewModel== value) return;
_currentViewModel= value;
OnPropertyChanged("CurrentViewModel");
}
}
I've edited the names for clarity and removed formatting information.
Any help greatly appreciated.
Cheers,
Daniel
EDIT: Came across the link How can I debug WPF bindings?. I set a break point on the Content binding and it does indeed only get called once when the binding is first set.
You should not be setting TwoWay as the mode on your ContentControl:
<ContentControl Content="{Binding CurrentViewModel, Mode=OneWay}"/>
This is because you intend your ContentControl to read the value, but never write it.
As an aside, you can also bind the ContentControl to the currently selected item in the collection, rather than to that property by doing this:
<ListBox ItemsSource="{Binding MyViewModelCollection}"
DisplayMemberPath="DisplayName"
IsSynchronizedWithCurrentItem="True"/>
<ContentControl Content="{Binding MyViewModelCollection/}"/>
The "slash" (/) at the end of the collection indicates the current item selected in the collection and setting that current item property is as simple as setting the IsSynchronizedWithCurrentItem equal to true.
A lot of times I find with this combination, I really don't need the extra property on my view model.
Anyway, I hope this helps.
Related
I have this collection
ObservableCollection<string> Urls { get; set; }
inside my data context class. I have a binding to it in my list box:
<ListBox ItemsSource="{Binding Urls}">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBox Text="{Binding .}" />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
The data is diplayed in the list box, the two corresponding-not-shown-here buttons with commands Add and Delete work as well, however, the changing the TextBox does not affect the contents of the collection.
I have tried Mode=TwoWay in binding, but I figured that it is turned on already. I have tried some other options like Validate=OnPropertyChange, however, there is still nothing get updated.
How to make the TextBox inside that templated items in ListBox actually update the Urls property of a datacontext class?
You cannot modify strings; use a wrapper class with one string property, then bind the TextBox to said property. That way the strings in the property can be replaced with the edited ones.
I'm building a graphical designer, based upon an article by Sukram in CodeProject. I'm now trying to extend it so that each item on the canvas binds to a different ViewModel object - i.e. I'm setting the DataContext for each item.
Every item on the designer is actually a ContentControl, into which is placed a different template (based upon which toolbox item was dragged onto the canvas). So I have a template containing a TextBox, and I have a ViewModel object containing a Name property, and I bind the Text property of the TextBox to the Name property of the ViewModel, and ... nothing. I've checked the visual tree with Snoop, and it confirms that the DataContext of the TextBox is the ViewModel object. Yet the TextBox remains empty. And if I modify the (empty) Text in the TextBox, the Name property in the ViewModel does not change. So it looks like the binding is not being applied (or has been removed somehow).
I've found a few posts which talk about the ContentControl messing around with the DataContext and Content properties, but I'm not sure how applicable they all are. The code sets the ContentControl.Content as follows:
newItem = new ContentControl();
ControlTemplate template = toolbox.GetTemplate();
UIElement element = template.LoadContent() as UIElement;
ViewModelItem viewModel = new ViewModelItem() { Name = "Bob" };
newItem.Content = element;
newItem.DataContext = viewModel;
and the XAML for the template is:
<ControlTemplate>
<Border BorderBrush="Black" BorderThickness="1" Width="100">
<TextBox Text={Binding Name}/>
</Border>
</ControlTemplate>
Snoop shows that the TextBox has a DataContext, and if I Delve that DataContext I can see that it has a Name property whose value is "Bob". So why does the TextBox remain empty? Snoop allows me to change that Name property, but the TextBox remains empty.
What am I doing wrong?
A few more details. I've set the VS2010 Debug DataBinding option for the OutputWindow to Verbose, which seems to show that the binding is all being attempted before I set the DataContext. Is it possible that the change to the DataContext is not being recognised?
I've just found this post DataTemplate.LoadContent does not preserve bindings - apparently DataTemplate.LoadContent does not preserve bindings. So it looks like I have to write my own version of LoadContent().
I've realised that the template has come through a XamlWriter, which apparently strips all bindings. This wouldn't be helping.
I've not been able to fix the DataTemplate.LoadContent(), but I realised that I didn't actually need a DataTemplate, since the XamlWriter / XamlReader was already instantiating the UI element that I was after. I found a fix to make the XamlWriter write all the bindings here, and after that it all works.
Thanks for your help.
Maybe you need to tell the binding in the ControlTemplate to look at the TemplatedParent, as is mentioned in this thread?
<TextBox Text="{Binding Path=Name, RelativeSource={RelativeSource TemplatedParent}}"/>
Either that, or try to use a DataTemplate instead.
I can't test this at the moment, so I might just be guessing here.
I would use a DataTemplate, as bde suggests.
You are trying to put some UI on your own data (ViewModel), and this is what Data-Templates are meant for (ControlTemplate is usually what you use if you want to change how e.g. a Button looks).
Change your code to use ContentControl.ContentTemplate with a DataTemplate:
<DataTemplate>
<Border BorderBrush="Black" BorderThickness="1" Width="100">
<TextBox Text={Binding Name}/>
</Border>
</DataTemplate>
Code-behind:
newItem = new ContentControl();
//NOTE: .GetTemplate() needs to return a DataTemplate, and not a ControlTemplate:
newItem.ContentTemplate = toolbox.GetTemplate();
ViewModelItem viewModel = new ViewModelItem() { Name = "Bob" };
newItem.Content = viewModel;
newItem.DataContext = viewModel;
<StackPanel DataContext="{StaticResource Employees1}">
<ListBox ItemsSource="{Binding}" DisplayMemberPath="Name"
IsSynchronizedWithCurrentItem="True"/>
<Label Content="{Binding Path=Count}"/>
<Label Content="{Binding Path=Name}"/>
</StackPanel>
How does the binding for the labels get resolved? How is it decided that the content of the second label is bound to Employees1.Count (and not to Employee.Count), while the first label is bound to
Employee.Name and synchonized with the listbox selection? Also, what if I would like to bind the first label to Employee.Count instead?
(Employee has properties Name (and possibly Count), Employees1 is an ObservableCollection of type Employee).
EDIT: So, the question here is WHY the first label displays the number of employees in the ObservableCollection, while the second label displays the name of a specific employee in the collection, the one that is currently selected in the ListBox. Apparently, the first label binds to the entire collection, and the second label to a specific employee in the collection. But why, and how to control this behavior.
From MSDN Data Binding Overview, Binding To Collections, section "Current Item Pointer":
Because WPF binds to a collection only by using a view (either a view
you specify, or the collection's default view), all bindings to
collections have a current item pointer.
and section "Master-Detail Binding Scenario":
This works because when a singleton object (the ContentControl in this
case) is bound to a collection view, it automatically binds to the
CurrentItem of the view.
In your example, the second Label automatically binds to the current item of the default view of the Employees1 collection. The first Label would also bind like this, but since the item object does not have a Count property it apparently falls back to a binding to the Count property of the collection itself. However i don't know if the latter behaviour is documented somewhere.
As Blam says - the labels have no relationship to the listbox - I think what you're trying to do here is bind an observableCollection of Employees with properties Count and Name to the listbox..
To do this you'll need an ItemsTemplate in the listbox
<ListBox ItemSource={Binding Employees1}>
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<Label Content="{Binding Count}" />
<Label Content="{Binding Name}" />
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
Let me try and answer the questions.
An ObservableCollection has a property Count.
As for getting a single property on the second label it is making some assumptions.
You might not get the same behavior in other version of .NET.
Should not bind a control that displays a single value to a collection.
If you want the selected item from the ListBox see this link
enter link description here
I have a ComboBox in my wpf application.
It's ItemsSource is binded to some table in my DataSet.
I need the text property to be binded to another's object property . I doesn't work because the ComboBox doesn't want to get two DataContexts. How can I solve this problem?
<StackPanel Width="Auto" Height="Auto" MinWidth="296" Orientation="Vertical" x:Name="MyStackPanel">
<ComboBox x:Name="MyComboBox" ItemsSource="{Binding}" Text={Binding Path=MyProperty} />
</StackPanel>
In the code behind :
MyComboBox.DataContext = MyDataSet.Tables[MyTable];
MyStackPanel.DataContext = MyObject;
I want the ComboBox to show items from one DataContext but to show the text from another DataContext. How can I do it?
Don't use DataContext. Set the Source property of your bindings in XAML or create the bindings in code and set the Source property there.
Why are you assigning something to the datacontext of the stackpanel? From the looks of it, its not used.
Your code should work if MyDataSet.Tables[MyTable] returns an enumeration and contains a property called MyProperty.
What do you mean when you say that the combobox "doesn't want to get two DataContexts"?
Look into the properties IsEditable and IsReadOnly of the combobox.
Something like
<ComboBox x:Name="MyComboBox" ItemsSource="{Binding}" Text={Binding ElementName=MyStackPanel Path=DataContext.MyProperty} />
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.