I've seen this question posted (and answered) a number of times, and I still can't seem to figure out what I'm missing...
I have a window with a list of checkboxes, and I want the ability to have checkboxes in the list enabled/disabled dynamically from code-behind. To do that I've got couple of radio buttons that call a code-behind function to toggle the 'Enabled' property of the first entry in the VisibleFeatures collection. Ideally, this would cause the first checkbox + text to enable/disable, but no UI changes occur.
What am I doing wrong?
ViewModel:
public class MyFeature
{
private bool _supported;
private bool _enabled;
private bool _selected;
public string Name { get; set; }
public bool Supported
{
get { return _supported; }
set { _supported = value; NotifyPropertyChanged("Supported"); }
}
public bool Enabled
{
get { return _enabled; }
set { _visible = value; NotifyPropertyChanged("Enabled"); }
}
public bool Selected
{
get { return _selected; }
set { _selected = value; NotifyPropertyChanged("Selected"); }
}
public MyFeature(string name)
{
Name = name;
_supported = false;
_enabled = false;
_selected = false;
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
public ObservableCollection<MyFeature> VisibleFeatures { get; set; }
void VisibleFeatures_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
if (e.NewItems != null)
foreach (MyFeature item in e.NewItems)
item.PropertyChanged += MyFeature_PropertyChanged;
if (e.OldItems != null)
foreach (MyFeature item in e.OldItems)
item.PropertyChanged -= MyFeature_PropertyChanged;
}
void MyFeature_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
// NotifyPropertyChanged() defined again elsewhere in the class
NotifyPropertyChanged("VisibleFeatures");
}
public Init()
{
VisibleFeatures = new ObservableCollection<MyFeature>();
VisibleFeatures.CollectionChanged += VisibleFeatures_CollectionChanged;
VisibleFeatures.Add(new MyFeature("Feature1"));
VisibleFeatures.Add(new MyFeature("Feature2"));
...
}
XAML:
<StackPanel>
<ListView ItemsSource="{Binding VisibleFeatures}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel IsEnabled="{Binding Enabled, Mode=TwoWay}">
<CheckBox IsChecked="{Binding Selected, Mode=TwoWay}">
<TextBlock Text="{Binding Name}" />
</CheckBox>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListView>
</StackPanel>
Your class MyFeature needs to declare that it implements interface INotifyPropertyChanged. Otherwise, there will be no listener generated from XAML to listen to your property change notification.
Beside, from your example, I see no use of notifying VisibleFeatures change.
Derive your class "MyFeature" from INotifyPropertyChanged interface.
Inorder to reflect your runtime changes made in your observable collection in view, it is mandatory to derive your viewmodel class (here MyFeature class) from INotifyPropertyChanged interface.
Also, it is advisable to use same instance of your binding property wherever it is used instead of creating a new instance.
Related
I am on a MVVM C# project.
I want to display a list of objects.
I want to add and remove items in this list and ALSO change items in this list.
So I choosed the BindingList<> over the ObservableCollection<>, which would not get noticed if an item has changed.
(I also tested the ObservableCollectionEx which is out there in the web, but this has the same behavior like the BindingList for me).
But the Listbox is not changing when items are changed.
(Adding and removing items is updated in the Listbox)
In my XAML
<ListBox DisplayMemberPath="NameIndex" ItemsSource="{Binding Profiles}" SelectedItem="{Binding SelectedProfile}">
or alternative with the ItemTemplate
<ListBox DockPanel.Dock="Right" ItemsSource="{Binding Profiles}" SelectedItem="{Binding SelectedProfile}" Margin="0,10,0,0">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding NameIndex}"/>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
In my ViewModel (ViewModelBase is implementing INotifyPropertyChanged etc)
public class ProfileListViewModel : ViewModelBase
{
private BindingList<Profile> profiles;
public BindingList<Profile> Profiles
{
get
{
return profiles;
}
set
{
profiles = value;
RaisePropertyChanged();
}
}
My items are also implementing INotifyPropertyChanged and I am calling OnPropertyChanged("Name") in my Setters.
My model
public class Profile : INotifyPropertyChanged
{
public Profile(){}
public int ProfileID { get; set; }
private string name;
public string Name
{
get
{
return name;
}
set
{
name = value;
OnPropertyChanged("Name");
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
Wiring the View with the ViewModel (BindingList is initialized before View)
ProfileListViewModel plvw= new ProfileListViewModel(message.Content);
var profileView = new ProfileListView(plvw);
profileView.ShowDialog();
In the View.xaml.cs
public ProfileListView(ProfileListViewModel plvw)
{
InitializeComponent();
DataContext = plvw;
}
When I am changing the name of an object then I get the ListChanged event to which I have subscribted in my ViewModel (Profiles.ListChanged += Profiles_ListChanged;) for testing BUT the items in the ListBox are NOT changing.
What am I doing wrong?
How can I get a updated Listbox?
Since your DisplayIndex is the computed property NameIndex, you need to call OnPropertyChanged("NameIndex") when its value changes due to a change in other properties, e.g.:
public string Name
{
get
{
return name;
}
set
{
name = value;
OnPropertyChanged("Name");
OnPropertyChanged("NameIndex");
}
}
Use
Profiles.ResetBindings() to bind it again.
I have the following setup:
XAML:
<ListBox x:Name="MyList" ItemsSource="{Binding MyItems}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<Image Height="20" Width="20" Visibility="{Binding HasInformation, Converter={StaticResource VC}, ConverterParameter=True}" Source="/path/to/information.png" />
<TextBlock Text="{Binding Name}" VerticalAlignment="Center" Padding="5,0" />
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
Note: The ConverterParameter being passed in simply controls whether the visibility is "Collapsed" (False), or "Hidden" (True), so in this case, I want the visibility to be Hidden.
ViewModel Snippet:
private ObservableCollection<IItem> _MyItems;
public ObservableCollection<IItem> MyItems
{
get
{
return _MyItems;
}
set
{
NotifyPropertyChanged(ref _MyItems, value, "MyItems");
}
}
private IItem _SelectedItem;
public IItem SelectedItem
{
get
{
return _SelectedItem;
}
set
{
NotifyPropertyChanged(ref _SelectedItem, value, "SelectedItem");
}
}
IItem:
public interface IItem
{
string Name { get; }
bool HasInformation { get; set; }
}
I populate an implementation of a list of IItem from a database into the list, and the information icon appears appropriately if HasInformation is true. This all works correctly.
However, if I set HasInformation by hand, the view does not update. I have tried:
In the ViewModel:
OnPropertyChanged("MyItems");
MyItems[MyItems.IndexOf(SelectedItem)].HasInformation = true;
// Note that "SelectedItem" is persisted correctly, and always
// points to the selected item that we want to update.
In the code behind:
MyList.GetBindingExpression(ItemsControl.ItemsSourceProperty).UpdateTarget();
All of these fire the getter of the MyItems property, but the view never updates and the icon never displays. I have ensured that the HasInformation property of the item that I updated does, in fact, remain true. I've attached to the PropertyChanged event to ensure that it's firing a property change for "MyItems" (it is, this also fires the getter), and I've even ensured that it's calling the value converter with the correct value for the HasInformation property (it is!), so what am I missing? Is there something weird with image showing/hiding or visibility value conversion that I'm not handling correctly?
ObservableCollection only notifies the collection changes not the changes in each of the item. In order to achieve your goal one of options is to change the IItem from interface to a class which implements INotifyPropertyChanged interface (or implement it in the IItem concrete type), and hook it with the ViewModel's PropertyChanged delegate (remember to unsubscribe it). See some of my code below.
ViewModel
public class MyViewModel: INotifyPropertyChanged
{
private ObservableCollection<Item> _MyItems;
public ObservableCollection<Item> MyItems
{
get
{
return _MyItems;
}
set
{
if (_MyItems != null)
{
foreach (var item in _MyItems)
{
item.PropertyChanged -= PropertyChanged;
}
}
if (value != null)
{
foreach (var item in value)
{
item.PropertyChanged += PropertyChanged;
}
}
OnPropertyChanged();
}
}
private Item _SelectedItem;
public Item SelectedItem
{
get
{
return _SelectedItem;
}
set
{
_SelectedItem = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
}
Item
public class Item : INotifyPropertyChanged
{
private string _name;
private bool _hasInformation;
public string Name
{
get { return _name; }
set
{
_name = value;
OnPropertyChanged();
}
}
public bool HasInformation
{
get { return _hasInformation; }
set
{
_hasInformation = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
var handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
}
I'm trying to setup a working two-way update by using this example.
These are the relevant code snippets:
XAML:
<Button Click="clkInit">Initialize</Button>
<Button Click="clkStudent">Add student</Button>
<Button Click="clkChangeStudent">Change students</Button>
(...)
<TabControl Name="tabControl1" ItemsSource="{Binding StudentViewModels}" >
<TabControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Path=StudentFirstName}" />
</DataTemplate>
</TabControl.ItemTemplate>
<TabControl.ContentTemplate>
<DataTemplate>
<Grid>
<Label Content="First Name" Name="label1" />
<TextBox Name="textBoxFirstName" Text="{Binding Path=StudentFirstName}" />
<Label Content="Last Name" Name="label2" />
<TextBox Name="textBoxLastName" Text ="{Binding Path=StudentLastName}" />
</Grid>
</DataTemplate>
</TabControl.ContentTemplate>
</TabControl>
Main Window:
public partial class MainWindow : Window
{
internal MainWindowViewModel myMWVM;
public MainWindow()
{
InitializeComponent();
}
private void clkInit(object sender, RoutedEventArgs e)
{
myMWVM= new MainWindowViewModel();
DataContext = myMWVM;
}
private void clkStudent(object sender, RoutedEventArgs e)
{
myMWVM.StudentViewModels.Add(new StudentViewModel());
}
// For testing - call a function out of the student class to make changes there
private void clkChangeStudent(object sender, RoutedEventArgs e)
{
for (Int32 i = 0; i < test.StudentViewModels.Count; i++)
{
myMWVM.StudentViewModels.ElementAt((int)i).changeStudent();
}
}
}
Main view:
class MainWindowViewModel : INotifyPropertyChanged
{
ObservableCollection<StudentViewModel> _studentViewModels =
new ObservableCollection<StudentViewModel>();
// Collection for WPF.
public ObservableCollection<StudentViewModel> StudentViewModels
{
get { return _studentViewModels; }
}
// Constructor. Add two stude
public MainWindowViewModel()
{
_studentViewModels.Add(new StudentViewModel());
_studentViewModels.Add(new StudentViewModel());
}
// Property change.
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
Student view:
class StudentViewModel : INotifyPropertyChanged
{
Lazy<Student> _model;
string _studentFirstName;
public string StudentFirstName
{
get { return _studentFirstName; }
set
{
if (_studentFirstName != value)
{
_studentFirstName = value;
_model.Value.StudentFirstName = value;
OnPropertyChanged("StudentFirstName");
}
}
}
string _studentLastName;
public string StudentLastName
{
get { return _studentLastName; }
set
{
if (_studentLastName != value)
{
_studentLastName = value;
_model.Value.StudentLastName = value;
OnPropertyChanged("StudentLastName");
}
}
}
public void changeStudent()
{
_model.Value.changeStudent();
}
public StudentViewModel()
{
_studentFirstName = "Default";
_model = new Lazy<Student>(() => new Student());
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
THE student:
class Student
{
public string StudentFirstName { get; set; }
public string StudentLastName { get; set; }
public Student()
{
MessageBox.Show("Student constructor called");
}
public Student(string nm)
{
StudentLastName = nm;
}
public void changeStudent()
{
StudentLastName = "McDonald";
}
}
If you read until here I already thank you :) Still, by calling "clkChangeStudent" I don't see the changes in the textbox. I guess it's because I don't call the set-method of the StudentViewModel. The project I'm working on is a bit complex and a lot of things happen in the class (here Student) itself.
How can I get a textbox update by settings values in the Student-class itself?
Your actual code clearly won't notify changes to the interface. The reason is simple. Your method that changes the student name is in the Student model and that model does not implement the INotifyPropertyChanged.
There is 2 solutions to fix this issue depending on one question, does the changeStudent() method has to stick with the object model, that is to say, can your requirements allows you to move the changeStudent() method to the view model?
If yes then, first solution, simply remove the changeStudent method from the model and move it to the view model like this:
class StudentViewModel : INotifyPropertyChanged
{
...
public void changeStudent()
{
this.StudentLastName = "McDonald";
}
}
In the other case, second solution, you have to raise events whenever a model property changes and then get your view model to suscribe to these changes. You can proceed like this in the model:
class Student : INotifyPropertyChanged
{
...
private string studentLastName;
public string StudentLastName
{
get
{
return this.studentLastName;
}
set
{
if(this.studentLastname != value)
{
this.studentLastName = value;
this.OnPropertyChanged("StudentLastName");
}
}
}
}
And for the view model:
class StudentViewModel : INotifyPropertyChanged
{
...
public StudentViewModel(Student model)
{
this._model = model;
this._model.PropertyChanged += (sender, e) =>
{
if(e.PropertyName == "StudentLastName")
{
this.OnPropertyChanged("StudentLastName");
}
};
}
}
Both solution will work. It is really import that you understand that your code explicitely needs to notifies the interface whenever a value changes.
ChangeStudent doesn't call any of the methods that trigger a property notify event in the view model, it alters the underlying model instead. It's these events that trigger the view to update itself.
As an aside you should also look at command binding from the view instead of using click handlers in the code-behind. That way your view doesn't need to know anything about the view model that's attached and can be pure presentation.
First you should use commands instead of events.
In your current structure you have to add an
OnPropertyChanged("StudentLastName");
call to your ChangedStudent() Method in StudentViewModel.
After that you have to set the UpdateSourceTrigger of the Bindings to PropertyChanged
Text="{Binding Path=StudentFirstName, UpdateSourceTrigger=PropertyChanged}"
I'm really new to WPF so apologies in adavnced if this is an obvious question. I have a simple Checkbox in XAML as
<ListBox ScrollViewer.VerticalScrollBarVisibility="Auto"
ItemsSource="{Binding Selections}" >
<ListBox.ItemTemplate>
<DataTemplate>
<Grid >
<CheckBox IsChecked="{Binding IsChecked}"
Content="{Binding Path=Item.SelectionName}" />
</Grid >
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
Simplified code behind to allow bindings and INotifyPropertyChanged is:
public ObservableCollection<CheckedListItem<Selection>> Selections { get; set; }
public class Selection
{
public String SelectionName { get; set; }
}
Selections = new ObservableCollection<CheckedListItem<Selection>>();
Selections.Add(new CheckedListItem<Selection>(new Selection()
{ SelectionName = "SomeName" }, isChecked: true));
public class CheckedListItem<T> : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private bool isChecked;
private T item;
public CheckedListItem()
{ }
public CheckedListItem(T item, bool isChecked = false)
{
this.item = item;
this.isChecked = isChecked;
}
public T Item
{
get { return item; }
set
{
item = value;
if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("Item"));
}
}
public bool IsChecked
{
get { return isChecked; }
set
{
isChecked = value;
if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("IsChecked"));
}
}
}
I now need to add an additional TextBox associated with each Checkbox, so in XAML I have
<ListBox ScrollViewer.VerticalScrollBarVisibility="Auto"
ItemsSource="{Binding Selections}" Margin="12,22,12,94">
<ListBox.ItemTemplate>
<DataTemplate>
<Grid >
<CheckBox IsChecked="{Binding IsChecked}"
Content="{Binding Path=Item.SelectionName}" />
<<TextBox />
</Grid >
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
I'm a bit stumped how to include this as part of the ObservableCollection and set it up the binding on both the CheckBox and associated TextBox? Both are being added together using Selections.Add(new CheckedListItem<Selection>(new Selection()
{ SelectionName = "SomeName" }, isChecked: true)); which is causing me some confusion.
EDIT: Added full code
public partial class SelectionSettingWindow : Window
{
public ObservableCollection<CheckedListItem<Selection>> Selections { get; set; }
public class Selection
{
public String SelectionName { get; set; }
public string SelectionTextField { get; set; }
}
public SelectionSettingWindow()
{
InitializeComponent();
Selections = new ObservableCollection<CheckedListItem<Selection>>();
string fg = #"Item1,true,TExtbox1text:Item2,true,TExtbox2text:Item3,false,TExtbox3text"; //Test String
string[] splitSelections = fg.Split(':');
foreach (string item in splitSelections)
{
string[] spSelectionSetting = item.Split(',');
bool bchecked = bool.Parse(spSelectionSetting[1].ToString());
string tbText = spSelectionSetting[2].ToString();
Selections.Add(new CheckedListItem<Selection>(new Selection()
{ SelectionName = spSelectionSetting[0].ToString(),
SelectionTextField = bText }, isChecked: bchecked));
}
DataContext = this;
}
public class CheckedListItem<T> : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private bool isChecked;
private T item;
private string textField;
public CheckedListItem()
{ }
public CheckedListItem(T item, bool isChecked = false)
{
this.item = item;
this.isChecked = isChecked;
}
public T Item
{
get { return item; }
set
{
item = value;
if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("Item"));
}
}
public bool IsChecked
{
get { return isChecked; }
set
{
isChecked = value;
if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("IsChecked"));
}
}
public string TextField
{
get { return textField; }
set
{
textField = value;
if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("TextField"));
}
}
}
}
<ListBox ScrollViewer.VerticalScrollBarVisibility="Auto"
ItemsSource="{Binding Selections}" Margin="12,22,12,94">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel>
<CheckBox IsChecked="{Binding IsChecked, Mode=TwoWay}"
Content="{Binding Path=Item.SelectionName}" />
<TextBox Text="{Binding Item.SelectionTextField, Mode=TwoWay}" />
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
replace SelectionTextField above with whatever the field is that needs to be edited using the textbox on your Selection class.
Note that I changed the <Grid> to a <StackPanel> So they wouldn't appear on top of eachother and changed the bindings to TwoWay so the changes are reflected in the model.
Make sure your Selection class implements INotifyPropertyChanged (ObservableCollection updates the UI when things get added to/removed from the collection, it doesn't know anything about notifying when it's content's properties change so they need to do that on their own)
Implementing INotifyPropertyChanged on many classes can be cumbersome. I find implementing a base class useful for this. I've got this along with an extra reflection helper for raise property changed available here and a snippet I've made available. It's silverlight but it should work fine for WPF. Using the code I've provided via download you can simply type proprpc and hit tab and visual studio will stub in a property that notifies on change. Some explanation is in one of my old blog posts here and gives credit for where I based the code and snippet from.
I'm using MVVM, VS 2008, and .NET 3.5 SP1. I have a list of items, each exposing an IsSelected property. I have added a CheckBox to manage the selection/de-selection of all the items in the list (updating each item's IsSelected property). Everything is working except the IsChecked property is not being updated in the view when the PropertyChanged event fires for the CheckBox's bound control.
<CheckBox
Command="{Binding SelectAllCommand}"
IsChecked="{Binding Path=AreAllSelected, Mode=OneWay}"
Content="Select/deselect all identified duplicates"
IsThreeState="True" />
My VM:
public class MainViewModel : BaseViewModel
{
public MainViewModel(ListViewModel listVM)
{
ListVM = listVM;
ListVM.PropertyChanged += OnListVmChanged;
}
public ListViewModel ListVM { get; private set; }
public ICommand SelectAllCommand { get { return ListVM.SelectAllCommand; } }
public bool? AreAllSelected
{
get
{
if (ListVM == null)
return false;
return ListVM.AreAllSelected;
}
}
private void OnListVmChanged(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == "AreAllSelected")
OnPropertyChanged("AreAllSelected");
}
}
I'm not showing the implementation of SelectAllCommand or individual item selection here, but it doesn't seem to be relevant. When the user selects a single item in the list (or clicks the problem CheckBox to select/de-select all items), I have verified that the OnPropertyChanged("AreAllSelected") line of code executes, and tracing in the debugger, can see the PropertyChanged event is subscribed to and does fire as expected. But the AreAllSelected property's get is only executed once - when the view is actually rendered. Visual Studio's Output window does not report any data binding errors, so from what I can tell, the CheckBox's IsSelected property is properly bound.
If I replace the CheckBox with a Button:
<Button Content="{Binding SelectAllText}" Command="{Binding SelectAllCommand}"/>
and update the VM:
...
public string SelectAllText
{
get
{
var msg = "Select All";
if (ListVM != null && ListVM.AreAllSelected != null && ListVM.AreAllSelected.Value)
msg = "Deselect All";
return msg;
}
}
...
private void OnListVmChanged(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == "AreAllSelected")
OnPropertyChanged("SelectAllText");
}
everything works as expected - the button's text is updated as all items are selected/desected. Is there something I'm missing about the Binding on the CheckBox's IsSelected property?
Thanks for any help!
I found the problem. It seems a bug existed in WPF 3.0 with OneWay bindings on IsChecked causing the binding to be removed. Thanks to this post for the assistance, it sounds like the bug was fixed in WPF 4.0
To reproduce, create a new WPF project.
Add a FooViewModel.cs:
using System;
using System.ComponentModel;
using System.Windows.Input;
namespace Foo
{
public class FooViewModel : INotifyPropertyChanged
{
private bool? _isCheckedState = true;
public FooViewModel()
{
ChangeStateCommand = new MyCmd(ChangeState);
}
public bool? IsCheckedState
{
get { return _isCheckedState; }
}
public ICommand ChangeStateCommand { get; private set; }
private void ChangeState()
{
switch (_isCheckedState)
{
case null:
_isCheckedState = true;
break;
default:
_isCheckedState = null;
break;
}
OnPropertyChanged("IsCheckedState");
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
var changed = PropertyChanged;
if (changed != null)
changed(this, new PropertyChangedEventArgs(propertyName));
}
}
public class MyCmd : ICommand
{
private readonly Action _execute;
public event EventHandler CanExecuteChanged;
public MyCmd(Action execute)
{
_execute = execute;
}
public void Execute(object parameter)
{
_execute();
}
public bool CanExecute(object parameter)
{
return true;
}
}
}
Modify Window1.xaml.cs:
using System.Windows;
using System.Windows.Controls.Primitives;
namespace Foo
{
public partial class Window1
{
public Window1()
{
InitializeComponent();
}
private void OnClick(object sender, RoutedEventArgs e)
{
var bindingExpression = MyCheckBox.GetBindingExpression(ToggleButton.IsCheckedProperty);
if (bindingExpression == null)
MessageBox.Show("IsChecked property is not bound!");
}
}
}
Modify Window1.xaml:
<Window
x:Class="Foo.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:vm="clr-namespace:Foo"
Title="Window1"
Height="200"
Width="200"
>
<Window.DataContext>
<vm:FooViewModel />
</Window.DataContext>
<StackPanel>
<CheckBox
x:Name="MyCheckBox"
Command="{Binding ChangeStateCommand}"
IsChecked="{Binding Path=IsCheckedState, Mode=OneWay}"
Content="Foo"
IsThreeState="True"
Click="OnClick"/>
<Button Command="{Binding ChangeStateCommand}" Click="OnClick" Content="Change State"/>
</StackPanel>
</Window>
Click on the button a few times and see the CheckBox's state toggle between true and null (not false). But click on the CheckBox and you will see that the Binding is removed from the IsChecked property.
The workaround:
Update the IsChecked binding to be TwoWay and set its UpdateSourceTrigger to be explicit:
IsChecked="{Binding Path=IsCheckedState, Mode=TwoWay, UpdateSourceTrigger=Explicit}"
and update the bound property so it's no longer read-only:
public bool? IsCheckedState
{
get { return _isCheckedState; }
set { }
}