I have an existing solution of my WPF UI but it's ViewModel implementation is clunky and I'm looking to improve.
Below is a gif of how my current system works:
There's a Current Task (note: only ever one item)
There's a Task List for Tasks (note: possibly many) that need to run in the future
When the user selects one list box, the other selection is removed
The problem is, I'm implementing Current Task as a Listbox with only one item. This means I have to lug around a backing IList for the ItemSource and another property for the SelectedItem.
Is there another control I can use to behave like ListBoxItem, but I can bind my CurrentTask directly to it and not have to muck around with an List for ItemSource as well?
EDIT: To get the selection to go away when one listbox is selected, I have a trigger set up on the SelectionChanged event.
(deleted my previous answer)
It occurs to me that at least part of the functionality you're looking for is implemented by the RadioButton class. Multiple RadioButtons in the same scope guarantee that only one of them is selected. You'll probably have to do a little work to make sure that your RadioButtons can be scoped correctly in your UI, and you'll probably need to retemplate some things to get exactly the UI you need. Additionally, RadioButton does not have a SelectedItem/SelectValue property to which it can write to, because WPF provides no built-in mechanism for multiple controls to safely bind to a "SelectedWhatever" property. But you could roll this yourself pretty easily with codebehind or triggers.
Here's the implementation I went with:
XAML View
<!-- The Current Task box -->
<ListBox x:Name="CurrentTaskBox" FlowDirection="RightToLeft" Background="{StaticResource WhiteBrush}">
<ListBoxItem IsSelected="{Binding CurrentTaskSelected, Mode=TwoWay}" Content="{Binding CurrentTask.TaskId}">
<i:Interaction.Triggers>
<i:EventTrigger EventName="Selected">
<command:EventToCommand Command="{Binding SetTaskDetailsFromCurrentTaskCommand}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</ListBoxItem>
</ListBox>
<!-- The Task List box -->
<ListBox x:Name="TaskListBox" SelectedIndex="{Binding TaskListIndex}" SelectedValue="{Binding TaskListSelection}" IsSynchronizedWithCurrentItem="True" HorizontalContentAlignment="Stretch" ItemsSource="{Binding TaskList}" FlowDirection="RightToLeft" DisplayMemberPath="TaskId" Margin="3">
<i:Interaction.Triggers>
<i:EventTrigger EventName="SelectionChanged">
<command:EventToCommand Command="{Binding SetTaskDetailsFromTaskListCommand}" CommandParameter="{Binding SelectedItem, ElementName=TaskListBox}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</ListBox>
ViewModel
/* Omitted most INPC property declarations...kinda boring */
public ICommand SetTaskDetailsFromCurrentTaskCommand { get { return new RelayCommand(SetTaskDetailsFromCurrentTask); } }
public ICommand SetTaskDetailsFromTaskListCommand { get { return new RelayCommand<TaskScheduleSequenceDto>(async taskSelection => await SetTaskDetailsFromTaskList(taskSelection)); } }
private bool _currentTaskSelected;
public bool CurrentTaskSelected
{
get
{
return _currentTaskSelected;
}
set
{
Set(() => CurrentTaskSelected, ref _currentTaskSelected, value);
}
}
private async Task SetTaskDetailsFromTaskList(TaskScheduleSequenceDto taskListSelection)
{
if (taskListSelection == null)
{
return;
}
var taskDetails = await _broker.RetrieveTaskDetails(taskListSelection.TaskId);
TaskDetails = taskDetails;
CurrentTaskSelected = false;
}
private void SetTaskDetailsFromCurrentTask()
{
TaskDetails = CurrentTask;
TaskListSelection = null;
CurrentTaskSelected = true;
}
This works fine and only requires that I have a single CurrentTask property in my VM, which I think is much cleaner.
Related
I have a datagridview populated with items and I am using a SelectionChanged event to populate textboxes from that data when selected.
If I make a selection, everything works. If I click elsewhere in the App and then come back to click the SelectionChanged event again on the same item - it doesn't work.
According to MSDN:
"This event occurs whenever there is a change to a selection."
MSDN SelectionChangedEvent
So it appears that despite clicking elsewhere, resetting the Textboxes - the selected item is not changing as the SelectionChanged event no longer triggers - click on another item and it works, click back again and it works - but click on it, reset textboxes, click it again - nothing happens, this includes clicking in the datagridview itself in a blank area.
XAML:
<DataGrid x:Name="TimeView" Grid.Row="1" Grid.Column="3"
Grid.ColumnSpan="3" Grid.RowSpan="4" Margin="10 50 10 10"
CanUserAddRows="False" Visibility="{Binding StartTiming}">
<i:Interaction.Triggers>
<i:EventTrigger EventName="SelectionChanged">
<cal:ActionMessage MethodName="SelectedTimeChangeEvent">
<cal:Parameter Value="$eventArgs" />
</cal:ActionMessage>
</i:EventTrigger>
</i:Interaction.Triggers>
</DataGrid>
ViewModel
public void SelectedTimeChangeEvent(SelectionChangedEventArgs e)
{
foreach (TimeData addedRow in e.AddedItems)
{
TbID = addedRow.ID;
TbDate = addedRow.Date;
TbStartTime = addedRow.StartTime;
TbDescription = addedRow.Description;
}
}
Since I am using MVVM and Caliburn, TimeView is connected to an ICollection, which is in turn connected to an ObservableCollection:
private ObservableCollection<TimeData>? _timeCollection;
public ObservableCollection<TimeData>? TimeCollection
{
get { return _timeCollection; }
set
{
_timeCollection = value;
NotifyOfPropertyChange(() => TimeCollection);
}
}
private ICollectionView? _timeView;
public ICollectionView? TimeView
{
get { return _timeView; }
set
{
_timeView = value;
NotifyOfPropertyChange(() => TimeView);
}
}
There is a work around, which is the following after populating the Textboxes:
TimeView = null;
TimeView = CollectionViewSource.GetDefaultView(TimeCollection);
This works, but I thought that there might be a "deselect" option that would be better than repopulating every time a selection is made, one of my Datagrids contains 15,000 items, and it is still instant, but seems overkill to populate it every time a selection is made.
i would recommend bindings, they automaticly reset when nothing is selected
<DockPanel>
<StackPanel DataContext="{Binding SelectedTime}" DockPanel.Dock="Left">
<TextBlock Text="{Binding ID}"/>
<TextBlock Text="{Binding Date}"/>
<TextBlock Text="{Binding StartTime}"/>
<TextBlock Text="{Binding Description}"/>
</StackPanel>
<DataGrid ItemsSource="{Binding TimeView}" SelectedItem="{Binding SelectedTime}">
...
</DataGrid>
</DockPanel>
public TimeData SelectedTime
{
get { return _selectedTime; }
set
{
_selectedTime = value;
NotifyOfPropertyChange(() => SelectedTime);
}
}
also there is this neet feature
protected virtual void SetValue<T>(ref T field, T value, [CallerMemberName] string propertyName = null)
{
field = value;
OnPropertyChanged(propertyName);
}
so you can write
set { SetValue(ref _selectedTime, value) }
I have a listview in WPF in an MVVM/PRISM app which may contain 1-to-many elements. When the listview contains only 1 element, and I select it, I cannot subsequently reselect it even though I set the SelectedIndedx value to -1. Worse, if I make the app update the listview with a different single element, I can't select that one either. The only way I can achieve selection of an item when it is the only item in the listview is to make the app display multiple items and select something other than the first. Then, when I make the app display a listview containing a single item, I can select it again - but only once.
In those cases where I cannot select the single item in the listview, the servicing routine never fires.
I tried implementing a XAML suggestion I found here using "Listview.Container.Style" and the IsSelected property, but that did not work.
My listview is fairly straightforward:
<ListView Name="lstEditInstance"
Grid.Row="5"
ItemsSource="{Binding Path=InstanceList,Mode=TwoWay}"
Width="488"
FontFamily="Arial" FontSize="11"
HorizontalAlignment="Left" VerticalAlignment="Stretch"
Margin="10,96,0,28"
SelectedIndex="{Binding Path=InstanceSelectedIndex}">
</ListView>
The servicing routine is:
private void OnInstanceSelectedIndexChanged()
{
// Handle case where user hits Enter without making a selection:
if (_instanceIndex == -1) return;
// Get the instance record for the row the user clicked on as a
// ResourceInstance class named "InstanceRecord".
InstanceRecord = _instanceList[_instanceIndex];
_instanceNumber = InstanceRecord.Instance;
FormInstName = InstanceRecord.InstName;
FormInstEnabled = InstanceRecord.Enabled;
FormInstState = InstanceRecord.InitialState;
FormInstIPAddress = InstanceRecord.IPAddress;
FormInstPort = InstanceRecord.Port.ToString();
FormInstSelectedURL = InstanceRecord.UrlHandler;
} // End of "OnResourceSelectedIndexChanged" method.
"InstanceList" is an observable collection.
I'd appreciate some suggestions. Thanks in advance for any help.
In a MVVM scenario, I'd use a ViewModel that contains the selected item instead:
class MyViewModel {
private IList<Item> instanceList= new List<Item>();
public IList<Item> List
{
get {return list; }
set {
list = value;
RaisePropertyChanged(() => List);
}
}
private Item selectedItem;
public Item SelectedItem {
get {return selectedItem;}
set {
selectedItem = value;
RaisePropertyChanged(() => SelectedItem);
}
}}
And the XAML:
<ListView Name="lstEditInstance"
Grid.Row="5"
ItemsSource="{Binding Path=InstanceList}"
Width="488"
FontFamily="Arial" FontSize="11"
HorizontalAlignment="Left" VerticalAlignment="Stretch"
Margin="10,96,0,28"
SelectedItem="{Binding Path=SelectedItem, Mode=TwoWay}}">
Notice that observableCollection is not required unless you have to modify the list items, in the same way the binding should be the default one for the list.
The SelectedItem / SelectedIndex should be TwoWay or Onewaytosource, the latter if you think you don't need to change the selectedItem programmatically
The service routine should be called from the ViewModel
EDIT:
your code of the service routine should be placed there:
set {
selectedItem = value;
// your code
RaisePropertyChanged(() => SelectedItem);
}
Another valid approach is to use Blend on XAML, by invoking a command on changed index and process under the ViewModel.
To do this, first add reference to System.Windows.Interactivity in your project and in XAML add
xmlns:interactivity="http://schemas.microsoft.com/expression/2010/interactivity
Then modify ListView with the following:
<ListView Name="lstEditInstance"
Grid.Row="5"
ItemsSource="{Binding Path=InstanceList}"
Width="488"
FontFamily="Arial" FontSize="11"
HorizontalAlignment="Left" VerticalAlignment="Stretch"
Margin="10,96,0,28"
SelectedItem="{Binding Path=SelectedItem, Mode=TwoWay}}">
<interactivity:Interaction.Triggers>
<interactivity:EventTrigger EventName="SelectionChanged">
<interactivity:InvokeCommandAction Command="{Binding YourCommand}"
CommandParameter="{Binding YourCommandParameter}" />
</interactivity:EventTrigger>
</interactivity:Interaction.Triggers>
I have a ViewModel with two ICollectionViews which are bound as ItemsSources to two different ListBoxes. Both wrap the same ObservableCollection, but with different filters. Everything works fine initially and both ListBoxes appear properly filled.
However when I change an item in the ObservableCollection and modify a property which is relevant for filtering, the ListBoxes don't get updated. In the debugger I found that SourceCollection for both ICollectionVIews is null although my ObservableCollection is still there.
This is how I modify an item making sure that the ICollectionViews are updated by removing and adding the same item:
private void UnassignTag(TagViewModel tag)
{
TrackChangedTagOnCollectionViews(tag, t => t.IsAssigned = false);
}
private void TrackChangedTagOnCollectionViews(TagViewModel tag, Action<TagViewModel> changeTagAction)
{
_tags.Remove(tag);
changeTagAction.Invoke(tag);
_tags.Add(tag);
}
The mechanism works in another context where I use the same class.
Also I realized that the problem disappears if I register listeners on the ICollectionViews' CollectionChanged events. I made sure that I create and modify them from the GUI thread and suspect that garbage collection is the problem, but currently I'm stuck... Ideas?
Update:
While debugging I realized that the SourceCollections are still there right before I call ShowDialog() on the WinForms Form in which my UserControl is hosted. When the dialog is shown they're gone.
I create the ICollectionViews like this:
AvailableTags = new CollectionViewSource { Source = _tags }.View;
AssignedTags = new CollectionViewSource { Source = _tags }.View;
Here's how I bind one of the two (the other one is pretty similar):
<ListBox Grid.Column="0" ItemsSource="{Binding AvailableTags}" Style="{StaticResource ListBoxStyle}">
<ListBox.ItemTemplate>
<DataTemplate>
<Border Style="{StaticResource ListBoxItemBorderStyle}">
<DockPanel>
<Button DockPanel.Dock="Right" ToolTip="Assign" Style="{StaticResource IconButtonStyle}"
Command="{Binding Path=DataContext.AssignSelectedTagCommand, RelativeSource={RelativeSource AncestorType={x:Type tags:TagsListView}}}"
CommandParameter="{Binding}">
<Image Source="..."/>
</Button>
<TextBlock Text="{Binding Name}" Style="{StaticResource TagNameTextBlockStyle}"/>
</DockPanel>
</Border>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
I use MvvmLight's RelayCommand<T> as ICommand implementation in my ViewModel:
AssignSelectedTagCommand = new RelayCommand<TagViewModel>(AssignTag);
I had this issue too, with a similar use-case. When I updated the underlying collection, I would call Refresh() on all the filtered views. Sometimes, this would result in a NullReferenceException thrown from within ListCollectionView.PrepareLocalArray() because SourceCollection is null.
The problem is that you shouldn't be binding to the CollectionView, but to the CollectionViewSource.View property.
Here's how I do it:
public class ViewModel {
// ...
public ViewModel(ObservableCollection<ItemViewModel> items)
{
_source = new CollectionViewSource()
{
Source = items,
IsLiveFilteringRequested = true,
LiveFilteringProperties = { "FilterProperty" }
};
_source.Filter += (src, args) =>
{
args.Accepted = ((ItemViewModel) args.Item).FilterProperty == FilterField;
};
}
// ...
public ICollectionView View
{
get { return _source.View; }
}
// ...
}
The reason for your issue is that the CollectionViewSource is getting garbage collected.
I am using PRISM to develop my Windows Phone app using the MVVM design pattern. I need to pass my SelectedItem object from my LongListSelector through my delegate command into my method.
I can do that. The problem is, I'm passing in the wrong object. I don't know if it's a design problem or I am binding improperly.
I need the object to be an Album object. What I'm getting instead is either null or my ViewModel. (I've changed the code a few times and those are the only things I can get.)
XAML
<phone:LongListSelector x:Name="AlbumList" ItemsSource="{Binding Albums}"
Margin="10,0,0,0" LayoutMode="Grid" GridCellSize="200, 200"
ItemTemplate="{StaticResource AlbumTemplate}"
toolkit:TiltEffect.IsTiltEnabled="True"
>
<i:Interaction.Triggers>
<i:EventTrigger EventName="SelectionChanged">
<i:InvokeCommandAction Command="{Binding DataContext.SelectAlbumCommand, ElementName=ContentPanel}"
CommandParameter="{Binding}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</phone:LongListSelector>
ViewModel
private ObservableCollection<Album> _albums;
public ObservableCollection<Album> Albums
{
get { return _albums; }
set
{
if (value != null)
{
_albums = value;
NotifyPropertyChanged();
}
}
}
private Album _selectedAlbum;
public Album SelectedAlbum
{
get { return _selectedAlbum; }
// code removed as it is not needed; the object is null when trying to set.
}
public void AlbumSelected(object p)
{
App.Dispatcher.BeginInvoke(() =>
{
SelectedAlbum = (Album)p;
});
////Navigate("/Views/PhotosListPage.xaml");
}
//command that takes an object as parameter.
_selectAlbumCommand = new DelegateCommand<object>(this.AlbumSelected);
In case you merely want to set the SelectedAlbum by your SelectAlbumCommand, why don't you try binding the SelectedItem to SelectedAlbum instead?
<phone:LongListSelector x:Name="AlbumList" ItemsSource="{Binding Albums}"
SelectedItem="{Binding SelectedAlbum}" />
In case you actually want to pass the SelectedItem to the SelectedAlbumCommand (for some other reason), you should bind the CommandParameter to the SelectedItem of the LongListSelector
<i:InvokeCommandAction Command="{Binding DataContext.SelectAlbumCommand, ElementName=ContentPanel}" CommandParameter="{Binding ElementName=AlbumList, Path=SelectedItem}"/>
Apparently, you cannot use LongListSelector for this. I had to change this to a listbox and it worked fine.
Had I searched harder, I would have found this: How to select an item in LongListSelector using the MVVM-pattern?
and this: WP8 LongListSelector SelectedItem not bindable
What I am attempting to do is have a collection of items shown in a GridView control and have the size of these items change based on a command executed by a separate button.
For example, having a row of buttons across the top reading “Small”, “Medium” and “Large” and having the items in the GridView respond to the relevant command by displaying its items in the relevant state.
I have the gridview declared like so
<GridView ItemsSource="{Binding Squares}"
With Squares being an observable collection of Square objects that have a Title and a Fill property.
At first I went down the DataTemplateSelector route by declaring the following data templates in the Resources section of the page.
<DataTemplate x:Key="SquareSmallTemplate">
<Grid Height="100" Width="100">
<Rectangle Fill="{Binding Fill}"/>
<TextBlock Text="{Binding Title}"/>
</Grid>
</DataTemplate>
<DataTemplate x:Key="SquareMediumTemplate">
<Grid Height="150" Width="150">
<Rectangle Fill="{Binding Fill}"/>
<TextBlock Text="{Binding Title}"/>
</Grid>
</DataTemplate>
<DataTemplate x:Key="SquareLargeTemplate">
<Grid Height="200" Width="200">
<Rectangle Fill="{Binding Fill}"/>
<TextBlock Text="{Binding Title}"/>
</Grid>
</DataTemplate>
The idea being that the grid’s height and width properties are different for the relevant template. I declared the following data templates in the selector
public DataTemplate SmallTemplate { get; set; }
public DataTemplate MediumTemplate { get; set; }
public DataTemplate LargeTemplate { get; set; }
And in the SelecteTemplateCore method I just returned the relevant template
protected override DataTemplate SelectTemplateCore(object item, DependencyObject container)
{
string value = item as string;
if (value != null)
{
if (value == "Small")
return SmallTemplate;
else if (value == "Medium")
return MediumTemplate;
else if (value == "Large")
return LargeTemplate;
return base.SelectTemplate(item, container);
}
else
{
return base.SelectTemplateCore(item, container);
}
}
However, with this method (and, by design of the DataTemplateSelector) the object being passed in is the item in the collection (the Square).
This is fine if I wanted each item to have a different appearance or something, but what I need is the template to change based on another property on the view model.
For this, I have the following
public string State {get; set;}
and this is set to “Small”, “Medium, or “Large based on a separate row of three buttons that execute a command that sets this property to the relevant value.
How do I relate the State property to changing to the relevant DataTemplate?
Another route I tried was to have a single Data template that used the VSM to animate the Height/Width properties in the relevant states. However I could not get the relevant animation to execute when the State changed.
Any help would be great, thanks
There are a few ways to do this, I'm not sure which would be best. In any case, you'll need 1) a trigger, and 2) the action to update the template. I am leaning towards using PropertyChangedTrigger along with an InvokeCommandAction.
<GridView x:Name="grid">
<i:Interaction.Triggers>
<ei:PropertyChangedTrigger Binding="{Binding State}">
<i:InvokeCommandAction Command="{Binding RelativeSource={RelativeSource AncestorType=UserControl},Path=UpdateTemplateCommand}" CommandParameter="{Binding State}" />
</ei:PropertyChangedTrigger>
</i:Interaction.Triggers>
<GridView>
(Here the "AncestorType" would just be the root of the view, so please change "UserControl" as needed.)
Then in the view, you would have an ICommand that updates the template:
UpdateTemplateCommand = new DelegateCommand(state => {
switch ((string)state)
{
default:
case "Small" : grid.ItemTemplate = "SquareSmallTemplate"; break;
case "Medium" : grid.ItemTemplate = "SquareMediumTemplate"; break;
case "Large" : grid.ItemTemplate = "SquareLargeTemplate"; break;
}
});
IDK ... after writing this out it seems a bit convoluted. Maybe you'd find it preferable to add a CurrentDataTemplate property to the view-model, and assign it by creating DataTemplates from strings using XamlReader.