I´m all out of ideas here
The thing is that Im using two comboboxes and I want to get values from both comboboxes to show content in DataGrid in wpf.
I have this function that gets values from both comboboxes. This works well.
private void cboxYearChange(object sender, SelectionChangedEventArgs e)
{
ComboBoxItem typeItemYear = (ComboBoxItem)comboBox2.SelectedItem;
string valueYear = typeItemYear.Content.ToString();
ComboBoxItem typeItemMonth = (ComboBoxItem)comboBox1.SelectedItem;
string valueMonth = typeItemMonth.Content.ToString();
}
But then I want to create another function to check for changes on the other combobox:
private void cboxMonthChange(object sender, SelectionChangedEventArgs e)
{
ComboBoxItem typeItemYear = (ComboBoxItem)comboBox2.SelectedItem;
string valueYear = typeItemYear.Content.ToString();
ComboBoxItem typeItemMonth = (ComboBoxItem)comboBox1.SelectedItem;
string valueMonth = typeItemMonth.Content.ToString();
}
I can build, but when I run this I get the Object reference not set to an instance of an object error on the ComboBoxItem typeItemYear = (ComboBoxItem)comboBox2.SelectedItem; line in the cboxMonthChange function
What am I missing here ?
SelectedItem is null until something is selected. Unless they both change at the same time (which is not possible as these events are fired in sequence), either the type cast on comboBox1.SelectedItem or comboBox2.SelectedItem will throw an exception.
Check if SelectedItem is set the methods.
Or use another cast, like:
ComboBoxItem item1 = comboBox1.SelectedItem as ComboBoxItem;
if (item1 != null)
{
// do something
}
Hope this helps :-)
1) you should not refer to control's name within the code whenever possible.
So you can know, for instance, which ComboBox was changed within a SelectionChanged
handler by casting the Sender to a ComboBox.
2) but in such a simple case, just use public properties and bind them to
your ComboBox : all will get done with no code.
<ComboBox x:Name="YearSelectCB" SelectedItem="{Binding SelectedYear}">
<ComboBox x:Name="MonthSelectCB" SelectedItem="{Binding SelectedMonth}">
(you can set the DataContext of the window in several ways, for instance in the
window loaded event handler (DataContext=this) )
Related
I created a WPF window to bind data in Datagrid based on the selection of date by the user.BY default it loads for a specific date which works fine. But When the date is changed, the grid is showing empty rows.but the observable collection I used is having data. The observable collection is of DataTable type.
Note: I used to set itemsource=null when there are no records since I am using the same grid for 2 different tables based on a radio button check.
I have set the public variable as Binding variable in the XAML, used INOtifyChanged interface.
My issues is when the same collection reloads, the Datagrid failed to bind and shows empty rows but generating columns. When the previous attempt set the itemsource as null, the current loading failed to load the column also.
Any generic scenario, I am facing,? Please help
My Code:
private ObservableCollection<DataTable> custInfoCol = new ObservableCollection<DataTable>();
public event PropertyChangedEventHandler PropertyChanged = delegate { };
private DataTable _CustInfo;
public DataTable CustInfo
{
get { return _CustInfo; }
set
{
_CustInfo = value;
PropertyChanged(this, new PropertyChangedEventArgs("CustInfo"));
}
}
private void rbPrev_Checked(object sender, RoutedEventArgs e)
{
custInfoCol.Clear();
custInfoCol.Add(CustInfo = showcustomer(cid));
}
Sounds like you might need to change the UpdateSourceTrigger in your binding:
Height="{Binding Height, ElementName=Day, UpdateSourceTrigger=PropertyChanged}"
I've had problems with the default behavior of it before, so now I just type it out every time.
https://msdn.microsoft.com/en-us/library/system.windows.data.binding.updatesourcetrigger%28v=vs.110%29.aspx?f=255&MSPPError=-2147217396
Based on this piece of code you provided in the comment:
<DataGrid ItemsSource="{Binding custInfo,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
DataContext="{Binding RelativeSource={RelativeSource AncestorType=Window}}"
I think there is typo in the Xaml. You should use ... Binding CustInfo... with capital C.
Of course, if AutoGenerateColumns is true, then I guess this is not the problem, because you wrote
Datagrid failed to bind and shows empty rows but generating columns
Which the Binding works. Therefore, you need to check showcustomer(cid) and make sure it contains the required DataRows.
I fixed the issue which is very simple. I had created the datatable instance as global and i changed it to local just before loading the executereader() method.It resolved the issue.
I'm trying to databind a combobox in WPF for the first time and I can't get it to happen.
The image below shows my code, can you please tell me what I am missing? I only want graphic stuff in the xaml.
private void Window_Loaded(object sender, RoutedEventArgs e)
{
Patient p = new Patient();
this.cbPatient.DataContext = p.SelfListAll();
this.cbPatient.DisplayMemberPath = "Name";
this.cbPatient.SelectedValuePath = "PatientIDInternal";
}
...
Short explanation: Just make the following change to your XAML:
<ComboBox ItemsSource="{Binding Path=patientList}" />
Then, in your Window_Loaded event handler, just add
this.DataContext = this
Then make a new member called patientList of type ObservableCollection<Patient>.
Long explanation:
You don't have a binding set up. You need to create one through XAML like this:
<ComboBox ItemsSource="{Binding Path=patientList}" />
Then, the combobox will look for a member or property called "patientList" on the object that is set as its DataContext. I'd recommend using an ObservableCollection for patientList.
Alternatively, to create one in code, you can follow the examples here:
http://msdn.microsoft.com/en-us/library/ms752347.aspx#specifying_the_binding_source
Binding myBinding = new Binding("patientList");
myBinding.DataContext = someObject; //whatever object has 'patientList' as a member
mycombobox.SetBinding(ComboBox.ItemsSourceProperty, myBinding);
This will set a binding on the mycombobox ComboBox with a path of patientList and a DataContext of someObject. In other words, mycombobox will show the contents of someObject.patientList (which would ideally be some ObservableCollection, so that updates to the collection notify the binding to update).
You need to actually add the binding, e.g.:
Binding binding = new Binding();
binding.Source = MySourceObject;
binding.Path = new PropertyPath("MyPropertyPath");
binding.Mode = BindingMode.OneWay;
BindingOperations.SetBinding(cbPatient, SomeDependencyProperty, binding);
Ok, here is the answer to how to populate a combobox in WPF. First, thanks to everyone above who made suggestions. The part I was missing was that I was not populating the ItemsSource property but the DataContext property. Again, thanks to everyone for their help.
private void Window_Loaded(object sender, RoutedEventArgs e)
{
Patient p = new Patient();
this.cbPatient.ItemsSource = p.SelfListAll();
this.cbPatient.DisplayMemberPath = "Name";
this.cbPatient.SelectedValuePath = "PatientIDInternal";
this.cbPatient.SelectedIndex = 0;
}
You need to set the ItemsSource property relative to the DataContext:
cbPatient.SetBinding(ItemsSourceProperty, new Binding());
EDIT
The ItemsSource property of the ComboBox is the property that should point to the collection of items to be shown.
The collection you are interested in, is in the DataContext.
The Binding is an object that keeps track of changes of the collection and reports them to the ComboBox and its Path is relative to the object in the DataContext.
Because the Binding also needs to know the ComboBox you use the static SetBinding method that ties the connection between ComboBox and the Binding.
As in your code the collection itself is in the DataContext, the Path is empty.
The ItemsSource property should point to the collection of Patients. Because the collection of Patients is already in the DataContext, the Binding's Path property is empty.
Suppose an class named Hospital has two properties: Patients and Docters (and perhaps more: Rooms, Appointments, ...) and you set the DataContext of the ComboBox to an instance of Hospital. Then you would have to set the Binding's Path Property to "Patients"
Now the ComboBox will display each item (Patient) in the collection. To specify how a single Patient should be displayed you need to set the ItemTemplate property of the ComboBox.
Does anyone know how I can do the equivalent XAML binding in code?
<DataGrid ... >
<DataGrid.Columns>
<DataGridTextColumn
Binding="{Binding Description}" <=== set in code **
/>
</DataGrid.Columns>
</DataGrid>
Cheers,
Berryl
=== UPDATE ====
It looks like the method I have been looking for is DataGridColumn.GenerateElement
If so, then the focus of this question is now how to set the Binding correctly. The reason I want to do this code is that my grid has 7 columns that are identical visually and whose data can be known by an index.
So I want to be able to simplify the xaml by using a subclass DataGridTextColumn which has an index property, and just have:
<DataGrid ... >
<DataGrid.Columns >
<local:DayOfWeekColumn Index="0" />
<local:DayOfWeekColumn Index="1" />
....
<local:DayOfWeekColumn Index="7" />
</DataGrid.Columns >
</DataGrid >
=== REVISED QUESTION ===
Assuming the Binding itself is logically and syntactically correct, what should the parameters to BindingOperations.SetBinding be??
protected override FrameworkElement GenerateElement(DataGridCell cell, object dataItem) {
var activity = (ActivityViewModel)dataItem;
var cellData = activity.Allocations[Index];
var b = new Binding
{
Source = cellData,
UpdateSourceTrigger = UpdateSourceTrigger.LostFocus,
Converter = new AllocationAmountConverter()
};
BindingOperations.SetBinding(??, ??, b);
return ??;
}
=== EDITS for ARAN =====
I am not overriding GenerateElement right now, but rather trying to get a static helper to set my binding for me. The helper is needed in any event to compensate for not being able to bind Header content in the current implementation of MSFT's DataGrid.
Basically the idea is to catch the DC from the grid and use it as necessary on each of the columns, which in this case would be the Header content, cell style, and Binding. Here is the code:
public class TimesheetDataGridColumnContextHelper
{
static TimesheetDataGridColumnContextHelper() {
FrameworkElement.DataContextProperty.AddOwner(typeof (DataGridTextColumn));
FrameworkElement.DataContextProperty.OverrideMetadata(
typeof (DataGrid),
new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.Inherits, OnDataContextChanged));
}
public static void OnDataContextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var grid = d as DataGrid;
if (grid == null || !grid.Name.Equals("adminActivityGrid")) return;
foreach (var col in grid.Columns) {
var dowCol = col as DayOfTheWeekColumn;
if (dowCol == null) continue;
var context = (IActivityCollectionViewModelBase) e.NewValue;
var index = Convert.ToInt32(dowCol.DowIndex);
_setHeader(dowCol, context, index);
var editStyle = (Style) grid.FindResource("GridCellDataEntryStyle");
dowCol.CellStyle = editStyle;
_setBinding(dowCol, index, context);
}
}
private static void _setBinding(DayOfTheWeekColumn dowCol, int index, IActivityCollectionViewModelBase context) {
dowCol.Binding = new Binding
{
Path = new PropertyPath(string.Format("Allocations[{0}]", index)),
UpdateSourceTrigger = UpdateSourceTrigger.LostFocus,
Converter = new AllocationAmountConverter()
};
}
private static void _setHeader(DataGridColumn col, IActivityCollectionViewModelBase context, int index)
{
var date = context.HeaderDates[index];
var tb = new TextBlock
{
Text = date.ToString(Strings.ShortDayOfWeekFormat),
ToolTip = date.ToLongDateString()
};
col.Header = tb;
}
}
}
Everything works except for the Binding. I can't tell if it's because my binding is wrong somehow (although I get no obvious errors) or this is not a good place to set it. The grid columns are just empty when I run it.
Any idea??
Cheers,
Berryl
=== FIXED! ===
The logic in the last update was actually correct, but getting lost in the internals of the DataGrid I missed that my Binding.Path was missing the property to be bound to! Credit to Aran for understanding the issue, realizing that GenerateElement overrides were not necessary, and catching that the Binding Source should not have been set.
You're always doing the fiddly grid bits eh Beryl?
Do a couple of things. Use reflector to look at the implementation of GenerateElement in the DataGridTextColumn. (.NET programmers live in reflector)
Now for the answer:
In the datagrid each column is not part of the visual tree. The column has two methods GenerateElement and GenerateEditingElement. These methods return the viewer and the editor for the cell respectively. In your method above you are not creating the viewer, which will probably be a TextBlock.
from reflector, the implementation of GenerateElement is as below, notice the first thing they do is create the viewer for the cell.
protected override FrameworkElement GenerateElement(DataGridCell cell, object dataItem)
{
TextBlock e = new TextBlock();
this.SyncProperties(e);
base.ApplyStyle(false, false, e);
base.ApplyBinding(e, TextBlock.TextProperty);
return e;
}
Once you have a textblock you can use the line below to set the binding on it.
BindingOperations.SetBinding(textBlock, TextBlock.TextProperty, binding);
I am not however convinced that you actually need to override the GenerateElement and GenerateEditingElement to get your desired effect. I think you could overide the Binding property of the base class and just modify the binding there with your extra field whenever it is set. This will mean everything else will just work and you wont end up removing functionality from your column. Once again a crawl through reflector looking at the class DataGridBoundColumn (the abstract base class) would be beneficial.
I do something similiar in one of our columns whenever a binding is set I modify the clipboard binding by adding an extra property so I can copy and paste effectively.
EDIT: Update...this should probably be another question but..
You are explicitly setting the source of the binding in your setBinding method. In the grid the source of the binding is the data contained in the row. You are setting it, which means it would be the same for each row. You can apply these funky bindings without the source property before the data context is set, the source becomes the item in each row, and your binding should reflect an index into the property held in each row.
Based on MSDN, it sounds like the first parameter of SetBinding() should be the control that you want to display the binding in (this in this case, assuming that GenerateElement() is a member of the DayOfWeekColumn class), and the second property is the property to bind the data to. I haven't used the WPF DataGrid very much, but I didn't see anything like a text property to set.
I do see that the DataGridTextColumn does have a Binding property, though. Maybe it would work to set it to the binding you created manually above?
How do I cancel a user selection in a databound WPF ListBox? The source property is set correctly, but the ListBox selection is out of sync.
I have an MVVM app that needs to cancel a user selection in a WPF ListBox if certain validation conditions fail. Validation is triggered by a selection in the ListBox, rather than by a Submit button.
The ListBox.SelectedItem property is bound to a ViewModel.CurrentDocument property. If validation fails, the setter for the view model property exits without changing the property. So, the property to which ListBox.SelectedItem is bound doesn't get changed.
If that happens, the view model property setter does raise the PropertyChanged event before it exits, which I had assumed would be enough to reset the ListBox back to the old selection. But that's not working--the ListBox still shows the new user selection. I need to override that selection and get it back in sync with the source property.
Just in case that's not clear, here is an example: The ListBox has two items, Document1 and Document2; Document1 is selected. The user selects Document2, but Document1 fails to validate. The ViewModel.CurrentDocument property is still set to Document1, but the ListBox shows that Document2 is selected. I need to get the ListBox selection back to Document1.
Here is my ListBox Binding:
<ListBox
ItemsSource="{Binding Path=SearchResults, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
SelectedItem="{Binding Path=CurrentDocument, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
I did try using a callback from the ViewModel (as an event) to the View (which subscribes to the event), to force the SelectedItem property back to the old selection. I pass the old Document with the event, and it is the correct one (the old selection), but the ListBox selection doesn't change back.
So, how do I get the ListBox selection back in sync with the view model property to which its SelectedItem property is bound? Thanks for your help.
For future stumblers on this question, this page is what ultimately worked for me:
http://blog.alner.net/archive/2010/04/25/cancelling-selection-change-in-a-bound-wpf-combo-box.aspx
It's for a combobox, but works for a listbox just fine, since in MVVM you don't really care what type of control is calling the setter. The glorious secret, as the author mentions, is to actually change the underlying value and then change it back. It was also important to run this “undo” on a separate dispatcher operation.
private Person _CurrentPersonCancellable;
public Person CurrentPersonCancellable
{
get
{
Debug.WriteLine("Getting CurrentPersonCancellable.");
return _CurrentPersonCancellable;
}
set
{
// Store the current value so that we can
// change it back if needed.
var origValue = _CurrentPersonCancellable;
// If the value hasn't changed, don't do anything.
if (value == _CurrentPersonCancellable)
return;
// Note that we actually change the value for now.
// This is necessary because WPF seems to query the
// value after the change. The combo box
// likes to know that the value did change.
_CurrentPersonCancellable = value;
if (
MessageBox.Show(
"Allow change of selected item?",
"Continue",
MessageBoxButton.YesNo
) != MessageBoxResult.Yes
)
{
Debug.WriteLine("Selection Cancelled.");
// change the value back, but do so after the
// UI has finished it's current context operation.
Application.Current.Dispatcher.BeginInvoke(
new Action(() =>
{
Debug.WriteLine(
"Dispatcher BeginInvoke " +
"Setting CurrentPersonCancellable."
);
// Do this against the underlying value so
// that we don't invoke the cancellation question again.
_CurrentPersonCancellable = origValue;
OnPropertyChanged("CurrentPersonCancellable");
}),
DispatcherPriority.ContextIdle,
null
);
// Exit early.
return;
}
// Normal path. Selection applied.
// Raise PropertyChanged on the field.
Debug.WriteLine("Selection applied.");
OnPropertyChanged("CurrentPersonCancellable");
}
}
Note: The author uses ContextIdle for the DispatcherPriority for the action to undo the change. While fine, this is a lower priority than Render, which means that the change will show in the UI as the selected item momentarily changing and changing back. Using a dispatcher priority of Normal or even Send (the highest priority) preempts the display of the change. This is what I ended up doing. See here for details about the DispatcherPriority enumeration.
In .NET 4.5 they added the Delay field to the Binding. If you set the delay it will automatically wait to update so there is no need for the Dispatcher in the ViewModel. This works for validation of all Selector elements like the ListBox's and ComboBox's SelectedItem properties. The Delay is in milliseconds.
<ListBox
ItemsSource="{Binding Path=SearchResults, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
SelectedItem="{Binding Path=CurrentDocument, Mode=TwoWay, Delay=10}" />
-snip-
Well forget what I wrote above.
I just did an experiment, and indeed SelectedItem goes out of sync whenever you do anything more fancy in the setter. I guess you need to wait for the setter to return, and then change the property back in your ViewModel asynchronously.
Quick and dirty working solution (tested in my simple project) using MVVM Light helpers:
In your setter, to revert to previous value of CurrentDocument
var dp = DispatcherHelper.UIDispatcher;
if (dp != null)
dp.BeginInvoke(
(new Action(() => {
currentDocument = previousDocument;
RaisePropertyChanged("CurrentDocument");
})), DispatcherPriority.ContextIdle);
it basically queues the property change on the UI thread, ContextIdle priority will ensure it will wait for UI to be in consistent state. it Appears you cannot freely change dependency properties while inside event handlers in WPF.
Unfortunately it creates coupling between your view model and your view and it's an ugly hack.
To make DispatcherHelper.UIDispatcher work you need to do DispatcherHelper.Initialize() first.
Got it! I am going to accept majocha's answer, because his comment underneath his answer led me to the solution.
Here is wnat I did: I created a SelectionChanged event handler for the ListBox in code-behind. Yes, it's ugly, but it works. The code-behind also contains a module-level variable, m_OldSelectedIndex, which is initialized to -1. The SelectionChanged handler calls the ViewModel's Validate() method and gets a boolean back indicating whether the Document is valid. If the Document is valid, the handler sets m_OldSelectedIndex to the current ListBox.SelectedIndex and exits. If the document is invalid, the handler resets ListBox.SelectedIndex to m_OldSelectedIndex. Here is the code for the event handler:
private void OnSearchResultsBoxSelectionChanged(object sender, SelectionChangedEventArgs e)
{
var viewModel = (MainViewModel) this.DataContext;
if (viewModel.Validate() == null)
{
m_OldSelectedIndex = SearchResultsBox.SelectedIndex;
}
else
{
SearchResultsBox.SelectedIndex = m_OldSelectedIndex;
}
}
Note that there is a trick to this solution: You have to use the SelectedIndex property; it doesn't work with the SelectedItem property.
Thanks for your help majocha, and hopefully this will help somebody else down the road. Like me, six months from now, when I have forgotten this solution...
If you are serious about following MVVM and don't want any code behind, and also don't like the use of the Dispatcher, which frankly is not elegant either, the following solution works for me and is by far more elegant than most of the solutions provided here.
It is based on the notion that in code behind you are able to stop the selection using the SelectionChanged event. Well now, if this is the case, why not create a behavior for it, and associate a command with the SelectionChanged event. In the viewmodel you can then easily remember the previous selected index and the current selected index. The trick is to have binding to your viewmodel on SelectedIndex and just let that one change whenever the selection changes. But immediately after the selection really has changed, the SelectionChanged event fires which now is notified via the command to your viewmodel. Because you remember the previously selected index, you can validate it and if not correct, you move the selected index back to the original value.
The code for the behavior is as follows:
public class ListBoxSelectionChangedBehavior : Behavior<ListBox>
{
public static readonly DependencyProperty CommandProperty
= DependencyProperty.Register("Command",
typeof(ICommand),
typeof(ListBoxSelectionChangedBehavior),
new PropertyMetadata());
public static DependencyProperty CommandParameterProperty
= DependencyProperty.Register("CommandParameter",
typeof(object),
typeof(ListBoxSelectionChangedBehavior),
new PropertyMetadata(null));
public ICommand Command
{
get { return (ICommand)GetValue(CommandProperty); }
set { SetValue(CommandProperty, value); }
}
public object CommandParameter
{
get { return GetValue(CommandParameterProperty); }
set { SetValue(CommandParameterProperty, value); }
}
protected override void OnAttached()
{
AssociatedObject.SelectionChanged += ListBoxOnSelectionChanged;
}
protected override void OnDetaching()
{
AssociatedObject.SelectionChanged -= ListBoxOnSelectionChanged;
}
private void ListBoxOnSelectionChanged(object sender, SelectionChangedEventArgs e)
{
Command.Execute(CommandParameter);
}
}
Using it in XAML:
<ListBox x:Name="ListBox"
Margin="2,0,2,2"
ItemsSource="{Binding Taken}"
ItemContainerStyle="{StaticResource ContainerStyle}"
ScrollViewer.HorizontalScrollBarVisibility="Disabled"
HorizontalContentAlignment="Stretch"
SelectedIndex="{Binding SelectedTaskIndex, Mode=TwoWay}">
<i:Interaction.Behaviors>
<b:ListBoxSelectionChangedBehavior Command="{Binding SelectionChangedCommand}"/>
</i:Interaction.Behaviors>
</ListBox>
The code that is appropriate in the viewmodel is as follows:
public int SelectedTaskIndex
{
get { return _SelectedTaskIndex; }
set { SetProperty(ref _SelectedTaskIndex, value); }
}
private void SelectionChanged()
{
if (_OldSelectedTaskIndex >= 0 && _SelectedTaskIndex != _OldSelectedTaskIndex)
{
if (Taken[_OldSelectedTaskIndex].IsDirty)
{
SelectedTaskIndex = _OldSelectedTaskIndex;
}
}
else
{
_OldSelectedTaskIndex = _SelectedTaskIndex;
}
}
public RelayCommand SelectionChangedCommand { get; private set; }
In the constructor of the viewmodel:
SelectionChangedCommand = new RelayCommand(SelectionChanged);
RelayCommand is part of MVVM light. Google it if you don't know it.
You need to refer to
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
and hence you need to reference System.Windows.Interactivity.
I came up against this recently, and came up with a solution that works well with my MVVM, without the need for and code behind.
I created a SelectedIndex property in my model and bound the listbox SelectedIndex to it.
On the View CurrentChanging event, I do my validation, if it fails, I simply use the code
e.cancel = true;
//UserView is my ICollectionView that's bound to the listbox, that is currently changing
SelectedIndex = UserView.CurrentPosition;
//Use whatever similar notification method you use
NotifyPropertyChanged("SelectedIndex");
It seems to work perfectly ATM. There may be edge cases where it doesnt, but for now, it does exactly what I want.
I had a very similar problem, the difference being that I am using ListView bound to an ICollectionView and was using IsSynchronizedWithCurrentItem rather than binding the SelectedItem property of the ListView. This worked well for me until I wanted to cancel the CurrentItemChanged event of the underlying ICollectionView, which left the ListView.SelectedItem out of sync with the ICollectionView.CurrentItem.
The underlying problem here is keeping the view in sync with the view model. Obviously cancelling a selection change request in the view model is trivial. So we really just need a more responsive view as far as I'm concerned. I'd rather avoid putting kludges into my ViewModel to work around limitations of the ListView synchronization. On the other hand I'm more than happy to add some view-specific logic to my view code-behind.
So my solution was to wire my own synchronization for the ListView selection in the code-behind. Perfectly MVVM as far as I'm concerned and more robust than the default for ListView with IsSynchronizedWithCurrentItem.
Here is my code behind ... this allows changing the current item from the ViewModel as well. If the user clicks the list view and changes the selection, it will immediately change, then change back if something down-stream cancels the change (this is my desired behavior). Note I have IsSynchronizedWithCurrentItem set to false on the ListView. Also note that I am using async/await here which plays nicely, but requires a little double-checking that when the await returns, we are still in the same data context.
void DataContextChangedHandler(object sender, DependencyPropertyChangedEventArgs e)
{
vm = DataContext as ViewModel;
if (vm != null)
vm.Items.CurrentChanged += Items_CurrentChanged;
}
private async void myListView_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
var vm = DataContext as ViewModel; //for closure before await
if (vm != null)
{
if (myListView.SelectedIndex != vm.Items.CurrentPosition)
{
var changed = await vm.TrySetCurrentItemAsync(myListView.SelectedIndex);
if (!changed && vm == DataContext)
{
myListView.SelectedIndex = vm.Items.CurrentPosition; //reset index
}
}
}
}
void Items_CurrentChanged(object sender, EventArgs e)
{
var vm = DataContext as ViewModel;
if (vm != null)
myListView.SelectedIndex = vm.Items.CurrentPosition;
}
Then in my ViewModel class I have ICollectionView named Items and this method (a simplified version is presented).
public async Task<bool> TrySetCurrentItemAsync(int newIndex)
{
DataModels.BatchItem newCurrentItem = null;
if (newIndex >= 0 && newIndex < Items.Count)
{
newCurrentItem = Items.GetItemAt(newIndex) as DataModels.BatchItem;
}
var closingItem = Items.CurrentItem as DataModels.BatchItem;
if (closingItem != null)
{
if (newCurrentItem != null && closingItem == newCurrentItem)
return true; //no-op change complete
var closed = await closingItem.TryCloseAsync();
if (!closed)
return false; //user said don't change
}
Items.MoveCurrentTo(newCurrentItem);
return true;
}
The implementation of TryCloseAsync could use some kind of dialog service to elicit a close confirmation from the user.
Bind ListBox's property: IsEnabled="{Binding Path=Valid, Mode=OneWay}" where Valid is the view-model property with the validation algoritm. Other solutions look too far-fetched in my eyes.
When the disabled appearance is not allowed, a style could help out, but probably the disabled style is ok because changing the selection is not allowed.
Maybe in .NET version 4.5 INotifyDataErrorInfo helps, I dont'know.
I've got a listbox that contains a list of objects (lets say addresses)
The list box items source is bound to this observable collection
<ListBox x:Name="listDetails"
ItemsSource="{Binding}"
...
Then i've got a text box, this is bound to the name fild of the current object
<TextBox x:Name="textBoxName" Text="{Binding Name, UpdateSourceTrigger=Explicit}" />
So I expect that the Name property of my current object won't be change unless i explicitly update it..
However it is getting updated... any ideas to why?
Also this is in a window, if i close the window and reopen the window somehow the same selection on the listbox is preserved..
I'd expected once the window was closed then it would forget all about the current selection of it's listbox?
Figured out how to solve it, i added an event to the listgbox
private void OnListValueChanged(object sender, SelectionChangedEventArgs e)
{
ListBox lb = e.Source as ListBox;
if (lb != null)
{
object dc = null;
if (lb.SelectedIndex != -1)
dc = lb.Items[lb.SelectedIndex];
gridDetails.DataContext = dc;
}
}
the grid details context was set independently each and every time.