I have a question regarding multiple user controls views with the same view model type. I can't seems to find specific answers for my confusion but this is quite speculative.
I have.
<StackPanel Orientation="Vertical">
<TextBlock Text="Signature Summary" FontSize="14" FontWeight="Bold" TextAlignment="Center" Height="30"/>
<my:ParameterFileSummaryView DataContext="{Binding ParamterFile1ViewModel}"/>
<my:ParameterFileSummaryView DataContext="{Binding ParamterFile2ViewModel}"/>
<my:ParameterFileSummaryView DataContext="{Binding ParamterFile3ViewModel}"/>
<my:ParameterFileSummaryView DataContext="{Binding ParamterFile4ViewModel}"/>
<my:ParameterFileSummaryView DataContext="{Binding ParamterFile5ViewModel}"/>
</StackPanel>
the stack panel is a container inside a main view which has a dependancy property view model datacontext used for a Prism/Unity IoC architecture.
These are therefore binding the datacontect for these individual views to properties of the interface of the main view via another interface.
It all seems to work ok and the binding of the elements in the ParameterFileSummaryView bind nicely to the values set on the, say for the first one, ParamterFile1ViewModel.
Which is exactly what I want. But of cource these ViewModels are built within the ViewModel of the main window and not out of the Unity container.... It all feels a little bit hacky. Is there a cleaner way to implement what I am attempting.
Apologies if it is really a moot question... but I can't see the wood for the trees. If the question confuses I will add edits, please be patient I am not an expert :) .
Question answered by myself and sanity checked by #Jon... Sorry SO for cluttering your questions board.
Related
It's a good thing I don't mind feeling stupid.
I'm trying to bind to an ObservableCollection on my view model. The data hierarchy looks like: Parent -contains list of- Child objects. Nothing complicated.
At the outermost grid of my Xaml tree I establish a link to the view model with:
<Grid DataContext="{StaticResource src}">
Yes, src does reference the view model and the two dozen bindings before the problem textbox work fine. There is not another DataContext in my Xaml tree. Now I come to a simple textbox. I want to bind Textbox text to a child.property.
This works:
<TextBlock
DataContext="{Binding Parent}"
Text="{Binding Path=Child.Property}"
Style="{StaticResource headerMajor}"
/>
This doesn't work:
<TextBlock
Text="{Binding Source=Parent,Path=Child.Property}"
Style="{StaticResource headerMajor}"
/>
I thought they were two ways of saying the same thing. Ordinarily I wonder for a moment and then keep on coding. However, some advice I've read mentioned that DataContext attributes buried in Xaml controls can lead to hard to find bugs.
Please explain why one works and the other does not. This will help my grasp on the whole binding topic.
Jim
Source is a property which holds an object used as source for the binding, it does not resolve to a property. Hence your binding is looking for the property path Child.Property on the string "Parent", see the problem?
Here's the question at its most basic: how do I listen for an update of what is changing in a TreeView control modified via a DragDropTarget?
So here's my deal: I have a TreeView that holds agenda items. All are of the same data type (WCFAgendaItem), and are loaded into a hierarchy with children expressed as a property ChildItems. The whole thing is wrapped up in an ObservableCollection and bound to the TreeView using MVVM Light. Works great to view. I also want users to be able to use drag and drop to reorder, reorganize and add new items to this agenda coming from a variety of other sources (one example is a ListView of image slides). All new items would also have the same data type of WCFAgendaItem, for consistency's sake and easy serialization.
Here's my issue: dragging and dropping works beautifully on the UI using the Toolkit's drag drop functionality. But I have no idea how to get the ViewModel to understand changes to the contents of the TreeView.
Code from the view (Agenda.xaml):
(up top)
<UserControl.Resources>
<AHHSTeam_SLClassroomManagerMVVM_Helpers_Converters:BooleanVisibilityConverter x:Key="BooleanVisibilityConverter"/>
<sdk:HierarchicalDataTemplate x:Key="hdtAgenda" ItemsSource="{Binding ChildItems, Mode=TwoWay}" >
<Grid HorizontalAlignment="Left">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="{Binding ImageThumbnailWidth}" />
<ColumnDefinition Width="250" />
</Grid.ColumnDefinitions>
<Image Grid.Column="0" Source="{Binding ThumbnailURL}" Width="{Binding ImageThumbnailWidth}" Height="{Binding ImageThumbnailHeight}" Visibility="{Binding HasImage, Converter={StaticResource BooleanVisibilityConverter}}" >
<ToolTipService.ToolTip>
<Image Source="{Binding ResizedImageURL}" />
</ToolTipService.ToolTip>
</Image>
<TextBlock Grid.Column="1" Text="{Binding Title}" TextWrapping="Wrap" />
</Grid>
</sdk:HierarchicalDataTemplate>
<Style TargetType="sdk:TreeViewItem" >
<Setter Property="IsExpanded" Value="True" />
</Style>
</UserControl.Resources>
(later on)
<controlsToolkit:TreeViewDragDropTarget Grid.Row="1" Grid.Column="0" x:Name="ddtAgenda" AllowDrop="True"
HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch" >
<sdk:TreeView Width="375" ScrollViewer.HorizontalScrollBarVisibility="Auto"
ScrollViewer.VerticalScrollBarVisibility="Visible" ItemsSource="{Binding DailyAgenda, Mode=TwoWay}" ItemTemplate="{StaticResource hdtAgenda}">
</sdk:TreeView>
</controlsToolkit:TreeViewDragDropTarget>
ViewModel code (AgendaViewModel.cs) --> I tried listening for CollectionChanged, so far that doesn't seem to work
(in constructor)
//add notification of agenda changes
DailyAgenda.CollectionChanged += new System.Collections.Specialized.NotifyCollectionChangedEventHandler(DailyAgenda_CollectionChanged);
(event)
void DailyAgenda_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
System.Windows.MessageBox.Show("Daily agenda updated, now has " + e.NewItems.Count.ToString() + " top-level elements.");
}
Code from model (WCFAgendaItem.cs)
[ContentProperty("ChildItems")]
public partial class WCFAgendaItem: INotifyPropertyChanged
{
private ObservableCollection<WCFAgendaItem> _childItems = new ObservableCollection<WCFAgendaItem>();
public ObservableCollection<WCFAgendaItem> ChildItems
{
get
{
return _childItems;
}
set
{
_childItems = value;
}
}
...
I am pretty sure that I get that listening for CollectionChanged isn't right in any case, given that this data doesn't just change at the top level. I looked at EventToCommand in Blend (MVVM Light, remember) but the only TreeView-specific event appears to be SelectionChanged, which doesn't seem right either. I looked at putting an EventToCommand trigger on the TreeViewDragDropTarget, but aren't those methods about overriding how the UI interactions happen? I don't think INotifyPropertyChanged on WCFAgendaItem is right for this either: although I'm going to want that later for editing item titles, it doesn't seem like it'll help me when items get moved around.
Maybe what I'm looking for is a stretch, but what I really want to have happen is for Silverlight to understand that the databinding works both ways on the ordering and contents of the WCFAgendaItem collection, and do all the collection reworking itself based on UI interactions. Then I could just listen for an update event after the collection is reworked - after that I can just crawl the modified ObservableCollection bound to the TreeView, and flatten/serialize/update via WCF.
Failing the ideal situation: I'm willing to crawl TreeViewItems if need be, but even if that's what I need to do I'm stuck on when to do it. Plus I need a way to pass all that back to the ViewModel so I'm not writing code behind. Do I need to attach to Drop() and rework the dropping logic? I found several old articles about custom drag drop implementations starting from the Toolkit, but nobody mentions how to save out the modified TreeView, especially in an MVVM situation.
finally {
While typing this out I found this article which may be useful, though that's a fair amount of work in the ViewModel. This is promising and I'll investigate, but I'm still holding out hope for something simpler. Also it looks like the Toolkit events have changed a little since the article was written.
}
I also had issues implementing this type of DragDrop functionality. The root cause seemed to be that neither the ItemDragCompleted event (EventHandler) nor ItemDroppedOnSource (DragEventHandler) pass the index at which the item was dropped.
I ended up subclassing the DragDropTarget in order to expose the protected method:
int GetDropTargetInsertionIndex(TItemsControlType dropTarget, DragEventArgs args)
I then used an attached behavior to assume responsibility for inserting items at the specified index into to the underlying collections.
I'm afraid the underlying code is too expansive to include in a StackOverflow answer (mainly due to extensive decoupling) but it's on my list of subjects to blog about. In the mean time, I hope the information above helps, it was certainly the key to the solution for me.
Ian
I'm fairly new to Data binding & XAML, so this probably is fairly simple thing but I've been stumped on it for days now (and frustrated with more googling than i can track at this point) and would appreciate any pointers in the right direction. My only preference is to keep it in pure XAML if possible.
In my RIA SL4 project, I have two Entities PackageOS and OS where PackageOS has an association to OS through PackageOS.OS (associating through PackageOS.OSID <-> OS.ID - and [Include] + .Include() setup properly on relevant sections)
This is the template (defined in Page.Resource section along with all other involved DDS) I'm using in DataForm to get OSEntities List to bind into PackageOS Entity (coming from RIA GetOSEntities() using DDS):
<DataTemplate x:Key="POSItemTemplate">
<StackPanel>
<toolkit:DataField Label="PackageOS.OS">
<TextBlock Text="{Binding Source={StaticResource packageOSEntityDomainDataSource}, Path=Data.CurrentItem.OS}" />
</toolkit:DataField>
<toolkit:DataField Label="OS">
<ComboBox ItemsSource="{Binding Path=Data, Source={StaticResource osEntityDomainDataSource}}"
SelectedItem="{Binding Path=Data.CurrentItem.OS, Source={StaticResource packageOSEntityDomainDataSource}}"/>
</toolkit:DataField>
</StackPanel>
</DataTemplate>
The core problem is SelectedItem of ComboBox is not working. All the bindings are reachable from IDE Binding wizard so it's not a problem of me typing incorrect path. I can see packageOSEntityDomainDataSource.Data.CurrentItem to be of type PackageOS.
If i create a manual entry in backend database, the result is shown in PackageOS.OS textblock so I know it is properly being returned but SelectedItem refuses to pick it up (it ends up selecting the first value in dropdown list regardless of OS item in PackageOS).
Many thanks in advance!
Finally figured this out. Leaving my answer in hopes that it saves somebody else the time that I spent on this.
First Lesson
The problem was in the fact that I didn't have a custom Equality implementation for generated entities and default reference equality didn't work as I was using two different instances. Once I implemented IEquatable on my generated entities (through .shared.cs partial classes on server side) everything started working like a charm.
For details please see Silverlight ComboBox Control Population by Manishdalal
Second lesson
Do not use multiple DDS controls if you can help it. Especially once you use a write operation on a DDS, you cannot load/refresh any other DDS that is sharing the DomainContext until changes are committed. The link above shows how to avoid multiple DDS by using list generators when all you want is to pick up list of entities to fill ComboBox up.
My new code looks like this:
<DataTemplate x:Key="POSItemTemplate">
<StackPanel d:DataContext="{Binding Source=packageOSDomainDataSource, Path=Data.CurrentItem}">
<toolkit:DataField Label="OS">
<ComboBox DisplayMemberPath="Name"
ItemsSource="{Binding Path=OSList, Source={StaticResource OSListGenerator}}"
SelectedItem="{Binding Path=OS, Mode=TwoWay}" />
</toolkit:DataField>
</StackPanel>
</DataTemplate>
Where OSListGenerator is returning an IEnumerable<OSEntity> through its OSList property after loading it from DomainContext
Third Lesson
In DDS DataTemplate you have to be explicit with TwoWay Binding. This is the new behaviour; something that took me days to figure as most of the tutorials I referred to were using SL3 and I didn't realize that this was a breaking change in DDS DataTemplate behaviour in SL4.
<Border BorderBrush="#C4C8CC" BorderThickness="0,0,0,1">
<TextBlock x:Name="SectionTitle" FontFamily="Trebuchet MS" FontSize="14" FontWeight="Bold" Foreground="#3D3D3D" />
</Border>
I have to use the same above format at many places in a single xaml page, so for this i created a usercontrol and defined the above code inside it.
So my question is,
What i am doing is it right approach?
Will it make the page to load slower then the above code used as it is without defining it in a new user control?
I doubt you would notice a difference. However a lighter and more flexiable approach would be to use a Templated Control instead of a UserControl. Its a little more technical but results in a tighter implementation.
How many is "many" anyhow?
I have a control bound to an Object and all is well but I want to turn it into a control template bound to different objects of a similar type. I would like to do this exclusively in xaml, if possible. Any good tutorials that outline the steps?
<TextBlock Text="{Binding Source={StaticResource BorderControl}, Path=ControlName}"/>
EDIT: With a little more experience, it turns out what I need is the ability to Set the Binding source based on a property of the control. i.e.
<TextBlock Text="{Binding Source={StaticResource {TemplateBinding Tag}}, Path=ControlName}"/>
The control exists within a ControlTemplate but works correctly if I bind it directly to the data -- if that makes a difference. I don't know if this is possible or if it's the correct approach. Any thoughts welcome!
EDIT:
This doesn't work either.
<TextBlock Text="{Binding Source={TemplateBinding Tag}, Path=ControlName}"/>
I think you want ContentPresenter here (http://msdn.microsoft.com/en-us/library/system.windows.controls.contentpresenter.aspx) - think of it as one line of an ItemsControl, it's got a content and a reference to a template that will represent that content.