This is the simplest example of a program that demonstrates the problem. I need to bind a List to ListBox. Yes, the data structure must be a list, not an ObservableCollection (but if it's needed, I can build a wrapper or something).
In this program there is a listbox and a button which removes the first item in the list. But when the item is removed, the ListBox contents are not updated even though oneway binding is configured. I need it to get updated on item removal.
class Data: INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private List<string> items;
public List<string> Items { get { return items; } }
public Data(List<string> items)
{
this.items = items;
}
public void RemoveFirstItem()
{
items.Remove(items[0]);
RaisePropertyChanged("Items");
}
private void RaisePropertyChanged(string p)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(p));
}
}
}
XAML code:
<Window x:Class="ListBoxTest.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid>
<ListBox Name="TheListBox" Margin="0,0,0.138,46.231" ItemsSource="{Binding Path=Items, Mode=OneWay}"/>
<Button Content="Button" HorizontalAlignment="Left" Margin="212,292,0,0" VerticalAlignment="Top" Width="75" Click="Button_Click"/>
</Grid>
</Window>
Window C# code:
public partial class MainWindow : Window
{
private Data data;
public MainWindow()
{
InitializeComponent();
data = new Data(new List<string>{ "1", "2", "3", "4" });
this.DataContext = data;
}
private void Button_Click(object sender, RoutedEventArgs e)
{
data.RemoveFirstItem();
}
}
Yes, the data structure must be a list, not an ObservableCollection (but if it's needed, I can build a wrapper or something)
It's pretty simple, The ListBox UI(Xaml) updating is all based on a few interfaces such as INotifyPropertyChanged, INotifyCollectionChanged and few more
These interfaces instruct the UI when an item they hold gets added / removed / refreshed ...
A List does not implement these interfaces(it implements things such as IEnumerable, ICollection...). So having your ListBox.ItemsSource bound to a collection of type List isn't going to get you the benefits of using an ObservableCollection with updates in the UI.
Sure, if you're forced to use a List and wouldn't mind how you're achieving the result, Every-time you remove an item from your List, reset the Window's DataContext (set the DataContext to null before the remove and again to data after the remove). However this is just insane if someone forced you to have to do that and you should prolly have a chat with them and explain why it's insane.
As for your wrapper idea, sure you can build your own custom collection that say implements IEnumerable, INotifyCollectionChanged, INotifyPropertyChanged and internally hold a List or whatever, but your ListBox.ItemSource should be of this type wrapper to get the updating behavior.
You haven't mentioned why exactly you are forced to not use an ObservableCollection<T>, however if you can you prolly should just use it than invent your own custom collection for simple stuff.
Related
I have list of strings and a property for it, only with get that returns List<string>. So, when I add something to my list and call OnPropertyChanged("NameOfProperty") it does not refresh my ItemsControl in the view, but when I add something in the constructor it works.
MainWindow
public MainWindow()
{
InitializeComponent();
DataContext = new MainWindowModel();
}
MainWindowModel C#
private static List<string> messages = new List<string>();
public List<string> Messages
{
get
{
return messages;
}
}
// ...
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
// ...
public void foo()
{
messages.Add("Hi");
OnPropertyChanged("Messages");
}
MainWindow XAML
<ScrollViewer Grid.Row="0" Grid.Column="1" Margin="10, 0, 0, 0" Grid.ColumnSpan="2">
<ItemsControl ItemsSource="{Binding Messages, Mode=OneWay}"/>
</ScrollViewer>
The expression
messages.Add("Hi");
does not change the value of the Messages property, and unless the property value has not actually changed, the PropertyChanged event is ignored.
In order to update the UI when a collection is modified (i.e. elements are added, moved or removed), the collection needs to implement the INotifyCollectionChanged interface. The framework provides the ObservableCollection<T> class that implements this interface.
public ObservableCollection<string> Messages { get; }
= new ObservableCollection<string>();
and just
Messages.Add("Hi");
Collection Properties which should notify the framework, that items were added or deleted must implement the interface INotifyCollectionChanged.
A default implementation is found in the ObservableCollection.
So you could change your Messages Property Type to ObservableCollection instead of List.
Changing lists to ObservableCollection should be enough.
I spend few hours on this working on bigger project, so I have made simple example. Problem is when you press "Add" button, it adds numbers to ComboBox item source property...Great, but when you open or select any item from comboBox, binding stops working.
I must be missing something.
XAML:
....
<Grid>
<ComboBox x:Name="comboBox" HorizontalAlignment="Left" Margin="82,63,0,0"
VerticalAlignment="Top" Width="120"/>
<Button x:Name="AddButton" Content="Add" HorizontalAlignment="Left"
Margin="82,143,0,0" VerticalAlignment="Top" Width="75"
Click="NewNumberClick"/>
</Grid>
...
C# code:
namespace ComboBoxBinding
{
public partial class MainWindow : Window, INotifyPropertyChanged
{
private List<double> _numbers;
Binding comboBoxBinding;
public List<double> Numbers
{
get
{
return _numbers;
}
set
{
_numbers = value;
OnPropertyChanged("Numbers");
}
}
public MainWindow()
{
InitializeComponent();
Numbers = new List<double>(){ 1.0, 2.0, 3.0};
comboBoxBinding = new Binding();
comboBoxBinding.Path = new PropertyPath("Numbers");
comboBoxBinding.Mode = BindingMode.TwoWay;
BindingOperations.SetBinding(comboBox, ComboBox.ItemsSourceProperty, comboBoxBinding);
DataContext = this;
}
private void NewNumberClick(object sender, RoutedEventArgs e)
{
Random rand = new Random();
double newNumber = 2.0 - rand.NextDouble();
Numbers.Add(newNumber);
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName = null)
{
if (PropertyChanged != null)
PropertyChanged.Invoke(this, new
PropertyChangedEventArgs(propertyName));
}
}
}
Use ObservableCollection instead of List. List don't provide a notification when somethings inside a list changes.
ObservableCollection is a collection that allows code outside the collection be aware of when changes to the collection (add, move, remove) occur. It is used heavily in WPF and Silverlight but its use is not limited to there. Code can add event handlers to see when the collection has changed and then react through the event handler to do some additional processing. This may be changing a UI or performing some other operation.
See: What is the use of ObservableCollection in .net?
your source is a List, it won't notify the UI about member updates. You could use ObservableCollection instead or call OnPropertyChanged each time after you do .Add
More importantly you should use a real DataContext instead of your UI class and you should do the binding in xaml not in code behind
This is kinda strange cause every example I found there says I'm doing things the right way yet I was unable to get my ComboBox binding to work in WPF.
I just created an empty WPF Application.
public List<string> myCollection { get; set; }
public MainWindow()
{
DataContext = this;
InitializeComponent();
myCollection = new List<string> {"test1", "test2", "test3", "test4"};
}
And here is my xaml for this:
<Window x:Class="WpfApplication2.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid>
<ComboBox ItemsSource="{Binding Path=myCollection}" Height="23" HorizontalAlignment="Left" Margin="66,56,0,0" Name="comboBox1" VerticalAlignment="Top" Width="319" />
</Grid>
I have tried Binding myCollection, Binding Path=myCollection, I have tried with and without setting DataContext.
Nothing seems to be working.
I have run out of ideas and every example I find out there says this is the correct way and it should be working so thanks for any help i advance.
Set the datacontext after InitializeComponent
InitializeComponent();
myCollection = new List<string> { "test1", "test2", "test3", "test4" };
DataContext = this;
at the end of your constructor
comboBox1.ItemsSource = myCollection;
Sajeetheran answer works because the initialize of the XAML objects looks at the current state and binds to what is there at that time but will fail if one changes the property to something else. I would term that a one-time work-around.
I just wanted to make this using bindings
For most WPF scenarios one wants to use the INotifyPropertyChange mechanision to allow for dynamic changes to be handled by the XAML bindings. If one wants to truly use the power of bindings it goes hand in hand with INotifyPropertyChange. Otherwise Dimitri's answer is just as valid as Sajeetharan's.
The binding does not know of the change because the reference of myCollection does not notify the world of a change in status; hence the data doesn't get displayed.
To facilitate such notification the class used to hold the property needs to adhere to INotifyPropertyChanged and the property myCollection needs to send a notify event. (Note in your case its the main window which is technically workable, but in the MVVM paradigm one wants to seperate the view from the dat and a ViewModel class is used to hold the actual data and provide this notificaiton).
public MainWindow : INotifyPropertyChanged
Then provide the event that will be subscribed to by the binding targets to the item on the DataContext :
public event PropertyChangedEventHandler PropertyChanged;
Then the mechanism to provide the change event.
/// <summary>
/// Raises the PropertyChanged event.
/// </summary>
/// <param name="propertyName">The name of the property that has changed.</param>
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = "")
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
Then provide the change for the myCollection
private List<string> _myCollection;
public List<string> myCollection
{
get { return _myCollection; }
set { _myCollection= value; OnPropertyChanged("myCollection"); }
}
public List<string> myCollection { get; set; }
public MainWindow()
{
myCollection = new List<string> {"test1", "test2", "test3", "test4"};
DataContext = this;
InitializeComponent(); //-- call it at the end
}
You have to InitializeComponent after assigning data context.
I've done this really simple example, is a Window with a TreeView and a Button. When you click the button you should see the selected item, but is not working, the CurrentItem property does not get updated when you change the selection:
C#:
using System.Collections.ObjectModel;
using System.Windows;
using System.Windows.Data;
namespace TreeViewSort
{
public partial class Window1
{
private ObservableCollection<string> _items;
public ListCollectionView SortedItems { get; private set; }
public Window1()
{
InitializeComponent();
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
_items =new ObservableCollection<string>();
_items.Add("ZZ");
_items.Add("AA");
_items.Add("CA");
_items.Add("DA");
_items.Add("EA");
this.SortedItems = new ListCollectionView(_items);
this.DataContext = this;
}
private void Button_Click(object sender, RoutedEventArgs e)
{
MessageBox.Show(this.SortedItems.CurrentItem.ToString());
}
}
}
XAML:
<Window x:Class="TreeViewSort.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300" Loaded="Window_Loaded">
<DockPanel>
<TreeView DockPanel.Dock="Top" Name="treeView1" ItemsSource="{Binding SortedItems, Mode=TwoWay}" MinHeight="200" />
<Button DockPanel.Dock="Bottom" Click="Button_Click">
Test
</Button>
</DockPanel>
</Window>
The MSDN documentation says
If the target is an ItemsControl, the current item is synchronized with the selected item
Any idea on why is this not working?
Thanks in advance.
Even when the documentation says that this will work with any ItemControl what I've read (and seen) is that it only works with Selectors ...
I'm not sure about CurrentItem in ListCollectionView, try to do this below:
Create a property in your Window1 class -> public string SelectedItem { get; set; }
In a XAML bind the tree view control SelectedItem property with your SelectedItem property.
Should work.
About SelectedItem -> http://msdn.microsoft.com/en-us/library/system.windows.controls.treeview.selecteditem.aspx
Regards
Pawel Jankowski
I had to do this and it wasn't pretty. I have a hybrid tree view / data grid. To be able to move to the next / previous item or move items up and down I had to do the following.
Add an IsSelected property to my model (hack - I know)
Each Model had a sort order property
When an item was selected in the tree - use linq queries to find any other items that were selected and mark as non selected
Mark the item that was just selected as IsSelected
Then use custom logic (by custom I mean 150 plus lines of code) to determine where the next item should be. This logic however was accounting for items that were collapsed in the tree and two levels (parent / child).
IIRC the reason I had to do this was the values I needed were on the visual tree but I was working with the logic tree.
In WPF I have a collection of bool? values and I want to bind each of these to a separate checkbox programmatically. I want the bindings to be TwoWay so that changing the value of the individual item in the collection in code updates the check box and vice versa.
I have spent ages trying to figure out how to do this and I am completely stuck. With the following code the checkbox only gets the right value when the window is loaded and that's it. Changing the check box doesn't even update the value in the collection. (UPDATE: this appears to be a bug in .NET4 as the collection does get updated in an identical .NET3.5 project. UPDATE: Microsoft have confirmed the bug and that it will be fixed in the .NET4 release.)
Many thanks in advance for your help!
C#:
namespace MyNamespace
{
public partial class MyWindow : Window, INotifyPropertyChanged
{
public MyWindow()
{
InitializeComponent();
DataContext = this;
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
public List<bool?> myCollection = new List<bool?>
{ true, false, true, false, true, false };
public List<bool?> MyCollection
{
get { return myCollection; }
set { myCollection = value; }
}
}
}
XAML:
<CheckBox IsChecked="{Binding Path=MyCollection[0], Mode=TwoWay}">
There are a few things that need changing here to get this to work. Firstly you'll need to wrap your boolean value in an object that implements the INotifyPropertyChanged interface in order to get the change notification that you are looking for. Currently you are binding to boolean values in your collection which do not implement the interface. To do this you could create a wrapper class like so :
public class Wrapper: INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
private bool val = false;
public bool Val
{
get { return val; }
set
{
val = value;
this.OnPropertyChanged("Val");
}
}
public Wrapper(bool val)
{
this.val = val;
}
}
You'll then want to create these objects in your form instead of a list of booleans. You may also want to use an observable collection instead of a list so that notification of items being added and removed are sent. This is shown below:
public Window1()
{
InitializeComponent();
this.DataContext = this;
}
private ObservableCollection<Wrapper> myCollection = new ObservableCollection<Wrapper>()
{new Wrapper(true), new Wrapper(false), new Wrapper(true)};
public ObservableCollection<Wrapper> MyCollection
{
get { return myCollection; }
}
The next thing to do is to display a list of check boxes in your ui. To do this WPF provides itemscontrols. ListBox is an itemscontrol so we can use this as a starting point. Set the itemssource of a listbox to be MyCollection. We then need to define how each Wrapper object is going to be displayed in the list box and this can be done with a datatemplate which is created in the windows resources. This is shown below :
<Window.Resources>
<DataTemplate x:Key="myCollectionItems">
<CheckBox IsChecked="{Binding Path=Val, Mode=TwoWay}"></CheckBox>
</DataTemplate>
</Window.Resources>
<Grid>
<ListBox ItemsSource="{Binding Path=MyCollection}" ItemTemplate="{StaticResource myCollectionItems}"></ListBox>
</Grid>
This should get you up and running with a simple demo of checkboxes that have values bound to a list of booleans.
What makes you think it's not working? It's working for me :)
Here's my test XAML:
<UniformGrid>
<CheckBox IsChecked="{Binding Path=MyCollection[0], Mode=TwoWay}"/>
<ListBox ItemsSource="{Binding MyCollection}"/>
<Button Content="Test" Click="Button_Click"/>
</UniformGrid>
Here's my code behind:
private void Button_Click(object sender, RoutedEventArgs e)
{
}
(the rest is the same as yours)
I placed a breakpoint on Button_Click and checked MyCollection[0] it was updated according to the IsChecked value of the CheckBox.
Try changing your collection type from List<bool?> to ObservableCollection<bool?> perhaps that is the reason you think it's not working for you (the fact that changes to the collection are not reflected anywhere else in your view).
Change your List<bool?> to an ObservableCollection<bool?>. A List does not raise the change notifications that WPF needs to update the UI. An ObservableCollection does. This handles the case where the list entry is changed and the CheckBox needs to update accordingly.
In the other direction, it works for me even with a List<bool?> -- i.e. toggling the checkbox modifies the value in the collection. Your binding syntax is certainly correct.