I have a combobox in my MainWindow window.
<ComboBox ItemsSource="{Binding GroupMethods}" SelectedItem="{Binding SelectedGroupMethod}"/>
I bind it to List which is in my base ViewModel class and it works at beginning.
I want that combobox to be everywhere in my application.
Now i switch DataContext of MainWindow to another viewModel which inherits from ViewModelBase (where the GroupMethods property is), i update that property in some point and see no results. Binding simply didn't recognise that DataContext has changed and still "looks" at previously saved property.
Fireing PropertyChanged event didn't solve the problem.
How do I make it work?
Related
I have a WPF control inheriting from ComboBox whose ItemsSource is bound to a list of elements, and whose SelectedItem is bound to another field. I have two references to the same list in my application: one resides in my MainWindow class, and one resides in my App class.
The list of elements used as the ItemsSource is assigned to the ComboBox at the time it is created. Thus, I expect to get an ItemsSourceChanged event.
The strange thing is, if the ItemsSource is bound to the MainWindow's list, then the ComboBox becomes populated with the correct SelectedItem drawn from the bound field. However, if I bind the ItemsSource to the App's copy of the list, then the SelectedItem becomes overwritten with null due to the ItemsSourceChanged event.
Here is the XAML for the ComboBox when it's binding to the App copy of the list:
<local:TagSelectionComboBox FilteredTagsList="{Binding Path=TagsList, Source={x:Static Application.Current}}" SelectedItem="{Binding TagValue}"></local:TagSelectionComboBox>
Here is the XAML for the ComboBox when it's binding to the MainWindow copy of the list:
<local:TagSelectionComboBox FilteredTagsList="{Binding TagsList, RelativeSource={RelativeSource AncestorType=Window}}" SelectedItem="{Binding TagValue}"></local:TagSelectionComboBox>
Here is the MainWindow's property used for binding:
public ObservableCollection<Tag> TagsList
{
get { return proj.Sim.Tags; }
}
And here is the App's property used for binding:
public ObservableCollection<Tag> TagsList
{
get { return proj.Sim.Tags; }
}
So these two properties on App and MainWindow are returning the same list. Stepping through in the debugger confirms: proj.Sim.Tags contains the same list in both cases.
Why does changing from one binding source to another alter the binding behavior? Is something else going on?
I've found that if I explicitly set IsSynchronizedWithCurrentItem="True", then the behavior is the same in both cases. So it's almost like IsSynchronizedWithCurrentItem="True" is the default behavior when I use the MainWindow (RelativeSource) binding but IsSynchronizedWithCurrentItem="False" is the default behavior when I use the App (x:Static) binding.
Background: the ComboBox-derived control in this question is basically the same as YantingChen's answer for this question:
Dynamic filter of WPF combobox based on text input
I have a WPF app with a MainWindow. The MainWindow consists of several CLR properties of type ObservableCollection. The MainWindow has a datagrid, whose ItemsSource property is bound to one of the observable collections (works fine). Next, I have a dialog. Its purpose is to display one of the observable collections from the main window in a datagrid. The dialog gets instantiated in the MainWindow. Initially I was passing the ObservableCollection to the dialog's constructor, and copying it into the dialog's CLR property. Then I would set the DataContext of the dialog to itself, and bind the ItemsSource property in the datagrid to the name of the CLR property. This worked fine.
Is there a better way to do this instead of passing the observable collection through the constructor? I tried setting the ItemsSource property of the Datagrid in the dialog to the observable collection in the MainWindow by using the GUI editor, which generated a binding using RelativeAncestor, but the data did not show. The problem is I have a bunch of dialogs that are meant to display data from the MainWindow, and I feel like there should be a simpler solution rather than passing everything to dialog's constructor. Also, would the dialogs be considered SubViews? The main window is a view.
Let's say your Dialog control is named DialogControl and has a DependencyProperty named Items defined in its code behind. In the XAML, I would bind this property to the DataGrid like this:
<DataGrid ItemsSource="{Binding Items, RelativeSource={RelativeSource Mode=
FindAncestor, AncestorType={x:Type DialogControl}}" />
This RelativeSource binding will go off and search through the properties of your DialogControl class and find the Items property. Note: Do NOT set the DataContext of the UserControl to itself.
Now in your MainWindow.xaml.cs file where you instantiate your DialogControl, you can set the Items property:
DialogControl dialogControl = new DialogControl();
dialogControl.Items = someCollection;
dialogControl.Show();
UPDATE >>>
Oh I see what you're after now... you want to bind from your UserControl to the actual collection in the MainWindow.xaml.cs file. You can still follow my advice, but instead of having the DependencyProperty in your DialogControl, you need to have it in your MainWindow.xaml.cs file. In that case, your binding in the UserControl would be:
<DataGrid ItemsSource="{Binding Items, RelativeSource={RelativeSource Mode=
FindAncestor, AncestorType={x:Type MainWindow}}" />
For this to work, the Items property must be a DependencyProperty.
I have a UserControl with 4 combobox bound to collections in viewmodel for that usercontrol.
I have used this control in a wpf form. This wpf form has its own viewmodel.
How do i access the text from the 4 comboboxes within the wpf form's viewmodel?
EDIT: i saw that you have different viewmodels. now it depends of the use of your usercontrol and the use of mvvm:)
you can use messenger or eventaggregator to comunicate the seleteditems from usercontrolviewmodel to mainviewmodel.
you can also use RelativeSource binding in your usercontrol to bind the selecteditem to your mainviewmodel directly (usercontrol then is just a composition of controls).
you can can rid of the usercontrol viewmodel and put all in the mainviewmodel and take my old example
you can create DependencyProperties for the SelectedItems in your usercontrol!(not usercontrol viewmodel!) and bind these to the properties in your mainviewmodel. i think thats the cleanest way if the usercontrol should be a real usercontrol.
old example:
in your viewmodel: //the real code should of course implement INotifyPropertyChanged and raise it properly
public ObservableCollection<string> MyFirstCollection {get; set;}//init once, add,remove,clear to alter
public string MySelectedCombobox1Value {get;set;}
in your usercontrol:
<ComboBox ItemsSource="{MyFirstCollection }" SelectedItem="{Binding MySelectedCombobox1Value, Mode=TwoWay}" />
thats all relating to your question. be sure that you set the DataContext right. you can check this with tools like snoop. the code i posted expected that the dataconext for the combobox is the viewmodel.
The UserControl should inherit the data context of the form you're adding it to which would be the view model. Any bindings in the UserControl would then be relative to the inherited data context. Have you tried binding to a view model property to ComboBox.Text?
UPDATE
Sorry, misread your question. Didn't see that the user control already has its own view model.
While it seems like there's a better approach, you could expose dependency properties on the user control that exposé the text of each combobox. Just thinking out loud.
The only clean way to do this is with binding, and the only way that would be recommended is if the user control exposes a DependencyProperty for the ViewModel or the individual text properties (as was suggested by sellmeadog) for consumption. Then you can have a property in the parent ViewModel that binds directly to that Dependency Property.
I have a view (MainPage.xaml) which is bound to a ViewModel.
In the ViewModel I have a DataModel property (note that both viewmodel & datamodel implements INotifyPropertyChanged, or what that interface is called).
In my view i have defined an ItemsControl whose ItemsSource is bound to the said property. This property (DataModel) has an ObservableCollection (which i know it populated with valid data).
The xaml snippet looks like this:
<ItemsControl ItemsSource="{Binding Path=CurrentDataModel.Items}">
Note that i am not showing the rest of the xaml. All it shows is the ItemsTemplate which is just a TextBlock.
The issue is that nothing is being drawn for this ItemsControl, even though i can clearly see (while debugging) that the collection has good data.
Is this "Path=..." binding not possible for an ItemsControl's ItemsSource?
The Path syntax looks correct. The most likely cause of failure is that either the DataContext is not set to your ViewModel or that the property path you specified is incorrect.
In your question you state that the ViewModel has a property named DataModel but in the xaml snippet you have CurrentDataModel.
I have a UserControl(a) with a stackpanel which has its ItemSource set to a collection.
The StackPanel then contains a set of UserControl(b) that contain a few buttons and a datagrid control.
Is there a way from the code behind in the UserControl(b) to access properties in the code behind of the parent UserControl(a).
Basically when UserControl(a) loaded into a window a parameter is passed in that contains whether the form will be considered read only or not. I would like bind the visibility of the buttons in Usercontrol(b) to the readonly property in the codebehind of the parent UserControl(a).
Normally with WPF I'd suggest you implement the Model-View-ViewModel pattern (see MSDN).
With this pattern you'd create a ViewModel with all of the data in that you want to bind. This would be set as the data context for the (a) usercontrol. That control would then bind all of it's controls to properties on the datacontext.
The child (b) usercontrol would inherit this datacontext and could therefore bind it's controls to the same properties as (a) uses. This is because datacontexts are inherited down the logical (and visual) tree until such point as it's overridden.
So for you I'd be looking at creating a ViewModel that contains the property ReadOnly. You can then set this ViewModel object as the datacontext for the (a) usercontrol. The (b) usercontrol, since it's under the (a) usercontrol hierarchy will inherit the same datacontext. This will then allow you to bind controls within (b) to the same properties as (a) as shown below.
<Button IsEnabled="{Binding ReadOnly}"
Context="Click me!"
Command="{Binding ClickMeCommand}" />
To set the datacontext in the view code-behind I do something like this constructor shown below.
public MyView(IMyViewModel viewModel)
{
InitializeComponent();
DataContext = viewModel;
}
MyView is the class that inherits from UserControl in your instance. You don't have to get the viewmodel in the way I have, I'm using Unity to inject the viewmodel into the views that are constructed automatically since I'm using Prism but you can just create it as a normal object and assign it to the datacontext.
Note that I've also bound the command to the button using the datacontext as I usually expose those via the ViewModel too, this is easy if you create a wrapper class that implements ICommand and proxies to a delegate. See DelegateCommand blog article or look at the DelegateCommand class in Prism if you are interested.
If for some reason you do override the datacontext, which can happen when using a master/details view where you change the datacontext of the details section of the view to be the currently selected item in the list, then you can still access the parent datacontext by using a relative source binding.
E.g.
<ComboBox Grid.Row="1" Grid.Column="1" x:Name="Unit" IsReadOnly="True"
ItemsSource="{Binding Path=DataContext.AvailableUnits, RelativeSource=
{RelativeSource Mode=FindAncestor,
AncestorType={x:Type Window}}}"
DisplayMemberPath="Name" SelectedItem="{Binding Unit}" />
Note the ItemsSource binding uses a relative source to find the parent window and then bind to a property of it's datacontext. I've also split the ItemsSource binding within the quotes across multiple lines for clarity here but don't do that in your xaml, I'm not sure it'll work there (not tried to see if markup extensions are that tolerant of whitespace).