Ok, hopefully this is simple but for some reason I can't find a straight answer and I'm not familiar enough with WPF yet to know how to do it.
I have a listview, it gets bound to an observable collection of objects to display. I want to have a context menu with a bunch of options. The options in the context menu are relative to the particular object in the list that was clicked on (things like delete, export, etc).
So I need the object that the user right clicked on in my listview to be passed as a parameter to the command that the context menu executes.
How do I do this?
Edit: I should mention I would prefer a solution that is mostly (if not entirely) xaml - I'm trying to avoid having significant code in the code-behind. If that's the only way to do it though...
Further Edit: More details that I forgot to mention that are important. The command I want executed is on the object bound to the data context of my user control, it is not on the objects in the list view. So I need the context menu's on the list view's items to be bound to a command that is on the user control's data context, and the listview item passed as a parameter into that command.
It depends on whether your ContextMenu is part of the template for individual items, or if it is attached to the ListBox as a whole.
If you are attaching your ContextMenu to the items in the list using a DataTemplate (this is generally the best way to do it), the DataContext on the MenuItem is already set so all you need to do is:
<MenuItem ... CommandParameter="{Binding}" />
On the other hand, if your ContextMenu is attached to the ListBox as a whole, you'll need to access the SelectedItem property of the ListBox:
<MenuItem ... CommandParameter="{Binding SelectedItem, RelativeSource={RelativeSource FindAncestor,ListBox,1}} />
Related
I have a list box that has a list of user controls. Each user control has 5 combo boxes. I want to be able to read the selected text of each combo box in each user control from the main application. However, when I change the selection in the combo box, the text property of the combo box in the user control doesn't change when I read it in the main application.
Code-behind:
radQueryParamList.Items.Add(new TCardQueryParameters());
Xaml (This is just a data template for how to display a TCardQueryParameters object):
<DataTemplate x:Key="TCardViewQueryParamDataTemplate">
<tcardqueryparam:TCardQueryParameters x:Name="TCardViewerParamUC" />
</DataTemplate>
<telerik:RadListBox Grid.Column="1" ItemTemplate="{StaticResource TCardViewQueryParamDataTemplate}" Name="radQueryParamList" VerticalAlignment="Top" HorizontalAlignment="Stretch" HorizontalContentAlignment="Stretch" Grid.ColumnSpan="3">
Where I loop over the list of user controls
string test = radTESTGACC.Text;//TEST combo box, Text property changes
//radQueryParamList is a listbox of user controls where TCardQueryParameters is the UC
foreach(TCardQueryParameters param in radQueryParamList.Items)
{
//Each UC has a radGACC combo box in it, and I am reading what the user
//selected for each user control here in the main app, but the text property
//never changes
String gacc = param.radGACC.Text; //Text property DOESN'T CHANGE
}
I thought that each instance of the user control would keep its own state and I would just be able to read what the user selected for that combo box, but that doesn't seem to be the case.
You have not bound the SelectedItem, SelectedValue, or SelectedIndex property of your internal ComboBox to anything so it maintains its selection.
An ItemTemplate is like a cookie cutter. It contains the definition of the object, but not the object itself. Properties specific to the object's state are lost unless they are bound to something on the DataContext behind the template.
This is important to note for two aspects.
First off, to improve performance WPF usually unloads items which are not visible, which often results in items being re-created from their template anytime they are reloaded. An example would be when you minimize an application to the taskbar, then maximize it again. This is usually better on performance and memory usage, however it does mean you have to be sure you store the state of items that were created with a Template somewhere.
And second, by default ListBoxes use something called virtualization. A simple way of explaining this would be this:
Suppose you have a ListBox of 100,000 items. In your ListBox, only 10 items can be visible at a time. WPF will render roughly 14 items (the 10 visible ones, and then a few extra for a scroll buffer so you don't see anything unusual while scrolling). When you scroll to new items, WPF just re-uses the existing items that are already rendered, and just replaces the DataContext behind those items.
As you can guess, it is far better on performance to render 14 UI items instead of 100k items.
So to answer your question, you will probably want to bind either SelectedItem, SelectedValue, or SelectedIndex of your TCardQueryParameters UserControl to a property on the DataContext (which in your case appears to be another different UserControl).
It should probably be noted that what you are essentially doing is creating a list of UserControls, assigning them to the ListBox, and then telling the ListBox that it should draw each UserControl with another separate UserControl. So although you are changing the SelectedItem in the template UserControl, that change is not being reflected to your ListBox.Items copy of the UserControl.
I'm guessing you probably don't want that, so would recommend removing your ItemTemplate completely.
Or better yet, create a new class object containing all the data for your UserControl, and adding that to your ListBox.Items. Then tell the ListBox to draw that item using a TCardQueryParameters UserControl as the ItemTemplate, like you have now.
I have a WPF Data Grid bound to an observable collection, which is working as intended.
What I am trying to do now is add text below it to say: "Number of selected rows: {count goes here}"
What's the proper way to do this? I could add a new property in the View Model called SelectedCount or something similar and bind to that, but it doesn't feel right. It seems redundant. Also, I could set the label text dynamically in the code behind, but I'm not sure if that's the "right" place to do this either.
Here's an example below.
EDIT:
Please pretend there's a checkbox column header whose intention is to provide check/uncheck all functionality. The state of this header checkbox should not count towards the final count.
You could use element binding to declaratively bind to the SelectedItems.Count property in XAML:
<TextBlock Text="{Binding ElementName=MyDataGrid,
Path=SelectedItems.Count, StringFormat=Number of selected rows: {0}}" />
Update
Presumably you're using MVVM, so adding a SelectedXCount property to your view model is a perfectly reasonable application of the view model. The advantage of having it in the view model is that you could unit test based on the number of selected items. E.g. if you want to check that the user can only progress (a CanNext property returns true) if the user has selected some items.
The SelectedItems property is not a DependencyProperty so can't be bound to, but there are many articles online that get around the issue when using the DataGrid in MVVM. Most of the solutions involve using a mechanism for calling a view model command on the invocation of the DataGrid's SelectionChanged event.
I have a WPF listview, and in one column the cell may contain one or more ListBoxes.
When I right-click a ListBox I'm building a context menu where each item has a DelegateCommand. Currently I'm setting the command parameter to a SelectedListBox property on the page viewmodel itself as my delegate command needs to know which ListBox has been right-clicked.
However this is leading to weird behaviour, which I'm assuming is because I'm binding multiple ListBoxes to the same page-level property (SelectedListBox).
The relevant XAML for the cell template for the listview is as follows:
<DataTemplate x:Key="MultipleListBoxCellTemplate">
<ListBox SelectedItem="{Binding Path=DataContext.SelectedListBox, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Page}}}" />
</DataTemplate>
Is there a better way to get which ListBox has been right-clicked to my viewmodel, or can anyone think of another approach? Much appreciated :)
When you are building the context menu, you know which list box was selected, yes? I would probably wrap that up in the ICommand you are binding the context item to. This way, each command knows exactly which ListBox it was created by and can get the selected item from there.
Alternately, you may be able to get around the issue with using SelectedItem by changing your binding to OneWayToSource so that the data only flows from the View back to the ViewModel. You may still have timing issues, which I suspect is your current problem, but depending on exactly what is going on, that may resolve it.
I have question on the checkbox.
First of all,
I have a usercontrol which has a list box like this and this user control will be switched by 2 button and then the data source is changed and then the the displayed officer status will be changed:
When I check the checkbox, Officers[0].IsOnDuty will be changed to true.
The problem is:
When I click another button and switch to another data source, this checked check box is still checked but the Officers[0].IsOnDuty for this data source is false.
How to solve this?
The data context of the list box item is an item for your officers collection, not the collection itself. And using a one way binding is incorrect, as the data source (the officer) will not be updated. So change the DataTemplate to:
<CheckBox IsChecked="{Binding Path=IsOnDuty, Mode=TwoWay}" />
*Here is the list box xaml:
<ListBox ItemsSource="{Binding OfficersCollection}">
<ListBox.ItemTemplate>
<DataTemplate>
<CheckBox IsChecked="{Binding Path=Officers[0].IsOnDuty, Mode=OneWay}" />
*
The problem with your approach is that once you change the ItemsSource (by switching to the next page) your chekcbox is still bound to the item of the first collection. I think this happens because you explicitly use an indexer for the binding Path=Officers[0].IsOnDuty
Your samplelist box xaml does not really make sense. the ItemsSoruce is a OfficerCollection and your ItemTemplate binds to a collection of Officers too. Depending on what you are trying to accomplish you should do one of the following:
If your are just interested in the first officer (as your sample suggest), add a DependencyProperty FirstOfficer (or a INotifyPropertyChanged) property to your collection and bind to it: IsChecked="{Binding Path=Officers.FirstOfficer, Mode=OneWay}"
If you however are interested in all Officers and want checkboxes for all of them you should create a DataTemplate for the Officer type and use this as the ItemTemplate.
Generally you can stay out of a lot of trouble if you stick with MVVM and really tailor your ViewModel objects very close to what the View needs so you can bind your View to the ViewModel in the simplest possible way. Think of the ViewModel as the View you want to build but without a visual representation.
I am trying to develop a filtering functionality for WPF DataGrid (from the WPF Toolkit). I want a user to right-click any cell and select Filter from its CcontextMenu, and then the grid should be filtered by the cell's value.
I am trying the M-V-VM pattern. My windows's datacontext is MainWindowViewModel which has a property Transactions. This property returns ObservableCollection<TransactionViewModel>, and the data grid uses this collection as its items source. So basically each row is bounded to TransactionViewModel (as you can guess, this grid lists transactions). MainWindowsViewModel has ICollectionView which is used for filtering and tracking the currently selected row. The DataGrid has its property IsSynchronizedWithCurrentItem set to "true", so myCollectionView.CurrentItem gives me the currently selected TransactionViewModel.
The only thing I still need to know is by which column I need to filter. This depends on where the user clicked the context menu. So I am trying to pass this information using CommandProperty of the context menu item. And here I have a real problem. I tried this:
CommandParameter="{Binding Column.Binding.Path.Path,
RelativeSource={RelativeSource FindAncestor,
AncestorType={x:Type tk:DataGridCell}}}" />
This is really ugly, but this works for DataGridTextColumns. Unfortunately, I have also DataGridTemplateColumns, and they don't work (the path is different there, because I need to reach the actual cell template)...
So how can I implement this functionality? Perhaps the whole way is wrong? I didn't find any valuable example on that. The only thing I found is the WPF DataGrid autofilter implementation on the Codeproject which doesn't work at all for some reason...
Thank you.
I'm not 100% sure if this would help but...
DataGrid has CurrentCell so you could bind it in TwoWay mode in your MainWindowViewModel.
Then every "row" could point to DoFilter command defined in MainWindowViewModel. It's not a beauty solution (because viewmodel has to know DataGrid Cell type) but it should work.
Why not just pass the cell as a parameter like this:
CommandParameter=
"{Binding RelativeSource={RelativeSource FindAncestor,tk:DataGridCell,1}}" />
and let your command's Executed event handle all the hard part of finding the actual column name? That way you can write all the special-case code you need.