I have an ObservableCollection and want to bind a Textbox to a specific element of that collection. The Items in the ObservableCollection are of a Type that implements INotifyPropertyChanged.
I have thought about creating a Property that selects the right element from the ObservableCollection, but then I would have to make this Property realise when the corresponding element in the Collection changes and I am not sure if this is the right way to do this.
Usually, especially if you use MVVM, you'll have a viewModel with your ObservableCollection and a property for the SelectedItem that you update with data binding.
For example, your viewModel could look like this:
class ProductsViewModel : INotifyPropertyChanged
{
public ObservableCollection<Product> Products { get; set; }
private Product _selectedProduct;
public Product SelectedProduct
{
get { return _selectedProduct; }
set
{
_selectedProduct = value;
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs("SelectedProduct"));
}
}
public ProductsViewModel()
{
Products = new ObservableCollection<Product>();
Products.Add(new Product() { Name = "ProductA" });
Products.Add(new Product() { Name = "ProductB" });
}
public event PropertyChangedEventHandler PropertyChanged;
}
Your window object xaml:
<Window x:Class="ProductsExample.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 HorizontalAlignment="Left" Height="171" Margin="32,29,0,0" VerticalAlignment="Top" Width="176"
ItemsSource="{Binding Products}"
SelectedItem="{Binding SelectedProduct, Mode=TwoWay}"
DisplayMemberPath="Name"
/>
<TextBox HorizontalAlignment="Left" Height="33" Margin="36,226,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="172"
Text="{Binding SelectedProduct.Name, Mode=TwoWay}"/>
</Grid>
</Window>
and the code-behind where you just set the datacontext:
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.DataContext = new ProductsViewModel();
}
}
Whenever you select a product in the listbox, the textbox is updated with the selected product, and if you change the product in the textbox (if product correctly implements INotifyPropertyChanged) the item in the listbox will also be updated.
Obviously you can achieve all this only using the code-behind, but for several reasons explained here:
http://msdn.microsoft.com/en-us/magazine/dd419663.aspx, it is better to have a ViewModel
If the item you need is specific by index you can access using the index
<TextBlock Text="{Binding MyItemsSource[2]}" />
To solve my problem I created a Property that selects the right element from the ObservableCollection and created an event Handler that is added to the CollectionChanged event of the ObservableCollection and raises the PropertyChanged Event for my SelectionProperty.
In code that looks something like this in the constructor of the class containing the ObservableCollection and the SelectionProperty:
myObservableColleciton.CollectionChanged +=
new NotifyCollectionChangedEventHandler(
myObservableCollection_CollectionChanged);
somewhere else in the class define this event handler:
void myObservableCollection_CollectionChanged(
Object sender, NotifyCollectionChangedEventArgs e){
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs("SelectionProperty"));
}
}
my selectionProperty looks something like this:
public User SelectionProperty
{
get { return myObservableCollection.First( user => user.id == 0); }
}
if the SelectionProperty depends on more than the ObservableCollection (maybe we want to find a user closest to a certain age, that is set elsewhere) then it needs to be made sure that the PropertyChanged event for SelectionProperty is raised as well, when those other properties change.
Related
Summary
I've got an element within a data template, that I want bound to some property of the main data context.
I realise that in this specific situation, a different solution may be preferable (and I have a working solution that avoids this), but I suspect this kind of problem may come up again and I want to know how to solve it in the general case.
Below are the specifics of my situation.
The Details
Data Hierarchy: I have a list of type A, each instance of A has a list of type B, each instance of B has some other data including a string for a text log.
UI Structure: I have a ComboBox to select an item of type A. I have a TabControl with the tabs representing items of type B, taken from the selected A above. In each tab, there is a means to enter data to populate the object of type B, and a log, representing changes to that instance of B.
Backing Logic: I track the selected item in each list with properties (SelectionA and SelectionB in the data context, MainWindowViewModel) that notify when they change. The B object also notifies when its log text changes. These ensure that the UI responds to changes to the backing data.
Problem: I want to move the notify logic to all be in one place (the DataContext, i.e. MainWindowViewModel), rather than having some in the B class and needing to duplicate the notify logic. To achieve this, I add a property (SelectionBLogText) to track the LogText property of the SelectionB object, and bind the log (in the templated tabpanel) to the main SelectionBLogText property. The problem is that within the tabpage, I can only seem to bind to properties of the selected B object (from the selected tab), and I need to bind to a property of the DataContext instead. I've tried using RelativeSource but nothing I've tried so far works, and the more I look at the docs the more I feel it's designed for another job.
The XAML (with irrelevant details removed):
<Window x:Class="WPFQuestion.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WPFQuestion"
mc:Ignorable="d"
Title="MainWindow"
Height="350"
Width="930">
<DockPanel>
<ComboBox
ItemsSource="{Binding ListOfA}"
SelectedItem="{Binding SelectionA}"
DisplayMemberPath="Name"/>
<TabControl
ItemsSource="{Binding SelectionA}"
SelectedItem="{Binding SelectionB}"
DisplayMemberPath="Name">
<TabControl.ContentTemplate>
<ItemContainerTemplate>
<StackPanel>
<TextBox
IsReadOnly="True"
Text="{Binding Path=???.SelectionBLogText}"/>
<Button Click="ClearLogButton_Click"/>
</StackPanel>
</ItemContainerTemplate>
</TabControl.ContentTemplate>
</TabControl>
</DockPanel>
</Window>
And the code-behind:
public partial class MainWindow : Window
{
internal MainWindowViewModel vm;
public MainWindow()
{
InitializeComponent();
vm = new MainWindowViewModel();
DataContext = vm;
}
// Various methods for event handling
}
public class A : IEnumerable<B>
{
public string Name { get; set; }
public List<B> Bs { get; set; }
}
public class B // previously : INotifyPropertyChanged
{
public string Name { get; set; }
public string LogText { get; set; }
// various other properties
}
public class MainWindowViewModel : INotifyPropertyChanged
{
private A _a;
private B _b;
public event PropertyChangedEventHandler PropertyChanged;
public List<A> ListOfA { get; set; }
public A SelectionA
{
get => _a;
set
{
if (_a == value)
{
return;
}
_a = value;
RaisePropertyChanged(nameof(SelectionA));
}
}
public B SelectionB
{
get => _b;
set
{
if (_b == value)
{
return;
}
_b = value;
RaisePropertyChanged(nameof(SelectionB));
RaisePropertyChanged(nameof(SelectionBLogText));
}
}
public string SelectionBLogText
{
get => SelectionB.LogText;
set
{
if (SelectionB.LogText == value)
{
return;
}
SelectionB.LogText = value;
RaisePropertyChanged(nameof(SelectionBLogText));
}
}
private void RaisePropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
have you tried something like this when you used relative binding? if not please check this out.
<TextBox IsReadOnly="True"
Text="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Window},
Path=Datacontext.SelectionBLogText}"/>
When i add/remove items from the list the listview is registered on, the item gets added/removed accordingly. But when i change a property of the list, resulting in a different ToString() value, the Listview doesn't update the change accordingly. If i reload the data after a restart of the app from a xml file, the ListView shows it's items accordingly. So i think i can exclude an issue with my ToString method. Or is it an issue that I'm using ToSTring() at all?
Does anyone know the solution to this issue?
window.xaml:
<Window x:Class="WpfApplication1.MainWin"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WpfApplication1"
mc:Ignorable="d"
DataContext="MainWindowViewModel"
Title="Baronieverwaltung für DSA" Height="1000" Width="1500"
WindowStartupLocation="CenterScreen"
WindowStyle="ThreeDBorderWindow">
<GroupBox Grid.Row="7" Grid.ColumnSpan="4" Header="Angestellte">
<ListView Height="200" ItemsSource="{Binding DieBaronie.Angestellte, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" SelectedIndex="{Binding SelectedAngestellterIndex}">
MainWindowViewModel.cs:
public class MainWindowViewModel : INotifyPropertyChanged
{
public Baronie DieBaronie { get; set; }
private void MethodThatChangesListViewItem()
{
if (SelectedAngestellterIndex > -1)
{
DieBaronie.Angestellte[SelectedAngestellterIndex].FunktionWarenschau = true;
}
//I found some threads where the solution was some variation of
//those NotifyPropertyChanged... but none work :(
NotifyPropertyChanged("DieBaronie.Angestellte");
NotifyPropertyChanged("DieBaronie");
NotifyPropertyChanged("");
NotifyPropertyChanged(null);
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(String propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (null != handler)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
DieBaronie.cs:
public class Baronie
{
public ObservableCollection<Angestellter> Angestellte { get; set; }
Angestellter.cs:
public class Angestellter : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
private Boolean _FunktionWarenschau { get; set; }
public Boolean FunktionWarenschau
{
get
{
return _FunktionWarenschau;
}
set
{
//if i add a break point here, the debugger stops here as expected - with the correct value
_FunktionWarenschau = value;
NotifyPropertyChanged();
}
}
//Method doesn't even get called after the change :(
public override string ToString()
{
String val = Name + " ";
if (_FunktionWarenschau)
{
val += "(Warenschau)";
}
return val;
}
Like you suggested, the issue is with ToString() - this is not a property, so the WPF binding engine is not aware of any need to refresh the view.
In addition, with more complex MVVM scenarios, I believe it is convention to use Properties anyway, as you may build out your views to display more complex data (e.g. images) or customize the layout of your data further (e.g. panel of images + strings).
To solve your problem, I would recommend:
Create a property in your ViewModel to bind to. Here, you could simply bind to FunktionWarenschau and Name. Alternatively, you can create a new string property and have FunktionWarenschau either update your string property or simply call NotifyPropertyChanged with the new property name passed along.
Create a DataTemplate for your ListView (untested code to give you a flavor)
<ListView Height="200"
ItemsSource="{Binding DieBaronie.Angestellte, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
SelectedIndex="{Binding SelectedAngestellterIndex}">
<ListView.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding FunktionWarenschau}"/>
<TextBlock Text="{Binding Name}"/>
</StackPanel>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
I have a ListView bounded to a List of a class I created. When doing an operating, it was supposed to add/remove items from the list, but my ListView wasn't updated even though I used INotifyPropertyChanged.
If I use ObservableCollection, it works but I need to have the list sorted, and ObservableCollection doesn't do sorting for WPF4.0 :(
Any way I can make the List binding work? Why didn't it work even though I used INotifyPropertyChanged?
XAML:
<ListView BorderThickness="0" ItemsSource="{Binding SelectedValues, UpdateSourceTrigger=PropertyChanged, Mode=OneWay}" Padding="5">
<ListView.View>
<GridView ColumnHeaderContainerStyle="{StaticResource myHeaderStyle}">
<GridViewColumn DisplayMemberBinding="{Binding Value}"></GridViewColumn>
VM:
private List<CheckBoxItem> _selectedValues = new List<CheckBoxItem>();
public List<CheckBoxItem> SelectedValues
{
get { return _selectedValues; }
set
{
_selectedValues = value;
OnPropertyChanged();
}
}
private void UnselectValueCommandExecute(CheckBoxItem value)
{
value.IsSelected = false;
SelectedValues.Remove(value);
//OnPropertyChanged("SelectedValues");
OnPropertyChanged("IsAllFilteredValuesSelected");
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
The CheckBoxItem class contains 2 properties, Value and IsChecked, which I don't think is relevant here.
So basically, I have a button which uses the UnselectValueCommandExecute to remove items from the list, and I should see the list updated in the UI, but I'm not.
When I debug, I can see the SelectedValues list updated, but not my UI.
You need a CollectionViewSource in your UI.
The XAML:
<Window x:Class="WavTest.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:scm="clr-namespace:System.ComponentModel;assembly=WindowsBase"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<CollectionViewSource Source="{Binding TestSource}" x:Key="cvs">
<CollectionViewSource.SortDescriptions>
<scm:SortDescription PropertyName="Order"/>
</CollectionViewSource.SortDescriptions>
</CollectionViewSource>
</Window.Resources>
<ListView ItemsSource="{Binding Source={StaticResource cvs}}" DisplayMemberPath="Description"/>
</Window>
The code behind:
namespace WavTest
{
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
var vm = new ViewModel();
this.DataContext = vm;
vm.TestSource.Add(new TestItem { Description="Zero", Order=0 });
}
}
public class ViewModel
{
public ObservableCollection<TestItem> TestSource { get; set; }
public ViewModel()
{
TestSource = new ObservableCollection<TestItem>();
TestSource.Add(new TestItem { Description = "Second", Order = 2 });
TestSource.Add(new TestItem { Description = "Third", Order = 3 });
TestSource.Add(new TestItem { Description = "First", Order = 1 });
}
}
public class TestItem
{
public int Order { get; set; }
public string Description { get; set; }
}
}
Explanation:
The ObservableCollection raises the PropertyChanged event as you expect, but you cannot sort it.
So, you need the CollectionView to sort it and bind the sorted collection to you ListView/ListBox.
As you can see, adding an element after the DataContext initialization affects the UI sorting the last added item ("Zero") correctly.
You need to use ObservableCollection because this raises a collection changed event which your wpf ListView will pick up on.
How about doing
Public ObservableCollection<object> MyList
{
get
{
return new ObservableCollection<object>(MySortedList);
}
}
and then whenever you change your sorted list raise a property changed event for MyList.
This obviously depends how you would like to sort your list as it might be possible to sort the ObservableCollection your question needs more info.
Objective: Set the visibility of a control based on the selected value of a ComboBox
Issue: The property that is being used to check the visibility is in the VM, however I don't know how to use it as DataContext is already defined to another object, i.e would I need to bind 2 datacontexts?!
Details:
I have a CustomControl that I load in my view associating to it a DataContext (a List of objects that is displayed as a grid:
<GUI:Counterparties_UserInputs x:Name="UserInputs" DockPanel.Dock="Right" DataContext="{Binding Source={StaticResource counterpartiesDataView}}"/>
In that user control I have some StackPanel which visibility should be triggered based on the selection of a ComboBox:
<ComboBox ItemsSource="{Binding Source={StaticResource CounterpartyTypes}}" SelectedValue="{Binding SelectedCounterpartyType}"/>
<StackPanel Visibility="{Binding Path=SelectedCounterpartyType,Converter={StaticResource SelectedValueToVisible}}"/>
The issue I have is that the code behind is never hit as I don't find how to associate an "extra" DataContext to the view.
Here is my code behind:
public partial class Counterparties_UserInputs : UserControl
{
...
public Counterparties_UserInputs()
{
// this.DataContext = _cptyUserInputsVM;
_cptyUserInputsVM = new Counterparties_UserInputs_VM();
InitializeComponent();
}
}
And the ViewModel where the Property "SelectedCounterpartyType" is never hit:
public class Counterparties_UserInputs_VM : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private string _selectedCounterpartyType;
public string SelectedCounterpartyType
{
get
{
return _selectedCounterpartyType;
}
set
{
_selectedCounterpartyType = value;
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs("SelectedCounterpartyType"));
}
}
}
}
I've seen that answer already but it's not exactly what I am doing... So would really appreciate your help! Thank you!
I have ObservableCollection items i want to bind this data to my comboBox.
How to bind data with comboBox?
I am using MVVM pattern so suggest me how to bind data using MVVM pattern
I am trying to do this code but not working properly..
In my XAML PAGE:
<ComboBox x:Name="comobo1"
DisplayMemberPath="CardTypeName"
SelectedValuePath="CardTypeID"
ItemsSource="{Binding Path=combodata}">
</ComboBox>
In my ViewModel
(Card is my model)
public ObservableCollection<Card> combodata = new ObservableCollection<Card>();
foreach (var item in App.db.States)
{
Card c = new Card(item.StateName, item.StateID);
combodata.Add(c);
}
How to bind this combodata to my comboBox - what am I doing wrong ?
At first: your combodata has private access modifier instead of public. At second: combodata must be property but not the field. And you'd better add INotifyPropertyChanged implementation to you class.
You have to bind to a public property of the view model that should implement INotifyPropertyChanged.
Here's what you should do:
View:
<ComboBox x:Name="comobo1" DisplayMemberPath="CardTypeName" SelectedValuePath="CardTypeID" ItemsSource="{Binding Path=ComboData}" />
ViewModel:
public class MyViewModel : INotifyPropertyChanged
{
private ObservableCollection<Card> comboData;
public event PropertyChangedEventHandler PropertyChanged;
public ObservableCollection<Card> ComboData
{
get
{
return this.comboData;
}
set
{
if (this.comboData != value)
{
this.comboData = value;
this.NotifyPropertyChanged("ComboData");
}
}
}
private void NotifyPropertyChanged(String info)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(info));
}
}
}
EDIT: you'll also need to set the DataContext property of your view. The simple way is to affect the instance of your ViewModel to the DataContext property in the code-behind of your view.
private ObservableCollection<Card> _combodata;
Public ObservableCollection<Card> comboData
{
get
{
if (_combodata == null)
_combodata = new ObservableCollection<Card>();
return _combodata;
}
set
{
if (value != _combodata)
_combodata = value;
}
}
<ComboBox x:Name="comobo1"
DisplayMemberPath="CardTypeName"
SelectedValuePath="CardTypeID"
ItemsSource="{Binding Path=comboData}">
</ComboBox>
And don't forget to set a DataContext property.
There are following problems with the code.
1.You can not bind to private field or property. It should be public property.
2.You only provided ItemsSource="{Binding Path=combodata}" but did not provide a source. Where does combodata come from ?
ObservableCollection has nothing to do unless your combo box items doe not change once filled. In this case List can work well.
To make it work, Change your combodata to public property as
public ObservableCollection<Card> combodata {get;set;}
then,
<ComboBox x:Name="comobo1"
DisplayMemberPath="CardTypeName"
SelectedValuePath="CardTypeID"
ItemsSource="{Binding Path=combodata}" ElementName=mainWindow>
</ComboBox>
by specifying ElementName you are telling WPF binding engine to look for the combodata property of the mainWindow class.
I hope this helps.
My best guess is your ComboBox's DataContext is not set to an instance of your ViewModel
I often use Snoop to debug DataContext problems with the application. It allows you to view your Visual Tree, and see what the DataContext is for all controls.
The DataContext is the data your UI is bound to. Usually the DataContext is set higher up in the Visual Tree, such as on the Window object, although as an example the following line of code would set the ComboBox's DataContext to a new instance of your ViewModel, and then your ComboBox should be able to find the combodata collection to bind to it.
comobo1.DataContext = new MyViewModel();
Also, change your combodata from a Field (no get/set accessor methods) to a Property (see Dmitriy's Answer for an example)
You need to bind to a public property. In your example, combodata is private.
Correct Answer is :
In XAML PAGE":
<CollectionViewSource x:Key="comboBoxCollection" Source="{Binding comboData}"></CollectionViewSource>
<DataTemplate x:Key="ComboBoxDataTemplate">
<Grid MinHeight="25">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<ComboBox x:Name="comobo1" DisplayMemberPath="CardTypeName" SelectedValuePath="CardTypeID" ItemsSource="{Binding Source={StaticResource comboBoxCollection }}">
</ComboBox>
</Grid>
</DataTemplate>
In ViewModel:
private ObservableCollection<Card> _combodata;
public ObservableCollection<Card> comboData
{
get
{
if (_combodata == null)
_combodata = new ObservableCollection<Card>();
return _combodata;
}
set
{
if (value != _combodata)
_combodata = value;
}
}
if (_objCardField.FieldTag == "State")
{
cards = new Cards();
foreach (var item in App.db.States)
{
Card c = new Card(item.StateName, item.StateID);
comboData.Add(c);
}
}