@ -1046,6 +1046,438 @@ namespace Avalonia.Controls.UnitTests
assetLoader : new StandardAssetLoader ( ) ) ) ;
}
[Fact]
public void Switching_Tab_Should_Preserve_DataContext_Binding_On_UserControl_Content ( )
{
// Issue #18280: When switching tabs, a UserControl inside a TabItem has its
// DataContext set to null, causing two-way bindings on child controls (like
// DataGrid.SelectedItem) to propagate null back to the view model.
// Verify that after switching away and back, the DataContext binding still
// resolves correctly.
using var app = UnitTestApplication . Start ( TestServices . StyledWindow ) ;
var viewModel = new TabDataContextViewModel { SelectedItem = "Item1" } ;
// Create a UserControl with an explicit DataContext binding,
// matching the issue scenario.
var userControl = new UserControl
{
[~UserControl.DataContextProperty] = new Binding ( "SelectedItem" ) ,
} ;
var target = new TabControl
{
Template = TabControlTemplate ( ) ,
DataContext = viewModel ,
Items =
{
new TabItem
{
Header = "Tab1" ,
Content = userControl ,
} ,
new TabItem
{
Header = "Tab2" ,
Content = "Other content" ,
} ,
} ,
} ;
var root = new TestRoot ( target ) ;
Prepare ( target ) ;
// Verify initial state
Assert . Equal ( 0 , target . SelectedIndex ) ;
Assert . Equal ( "Item1" , userControl . DataContext ) ;
// Switch to second tab and back
target . SelectedIndex = 1 ;
target . SelectedIndex = 0 ;
// The UserControl's DataContext binding should still resolve correctly.
Assert . Equal ( "Item1" , userControl . DataContext ) ;
// Verify the binding is still live by changing the source property.
viewModel . SelectedItem = "Item2" ;
Assert . Equal ( "Item2" , userControl . DataContext ) ;
}
[Fact]
public void TabItem_Child_DataContext_Binding_Should_Work ( )
{
// Issue #20845: When a DataContext binding is placed on the child of a TabItem,
// the DataContext is null. The binding hasn't resolved when the content's
// DataContext is captured in UpdateSelectedContent, so the captured value is null.
using var app = UnitTestApplication . Start ( TestServices . StyledWindow ) ;
var viewModel = new MainViewModel ( ) ;
var tab1View = new UserControl ( ) ;
tab1View . Bind ( UserControl . DataContextProperty , new Binding ( "Tab1" ) ) ;
// Add a child TextBlock that binds to a property on Tab1ViewModel.
var textBlock = new TextBlock ( ) ;
textBlock . Bind ( TextBlock . TextProperty , new Binding ( "Name" ) ) ;
tab1View . Content = textBlock ;
var target = new TabControl
{
Template = TabControlTemplate ( ) ,
DataContext = viewModel ,
Items =
{
new TabItem
{
Header = "Tab1" ,
Content = tab1View ,
} ,
} ,
} ;
var root = new TestRoot ( target ) ;
Prepare ( target ) ;
// The UserControl's DataContext should be the Tab1ViewModel.
Assert . Same ( viewModel . Tab1 , tab1View . DataContext ) ;
// The TextBlock should display the Name from Tab1ViewModel.
Assert . Equal ( "Tab 1 message here" , textBlock . Text ) ;
}
[Fact]
public void TabItem_Child_With_DataContext_Binding_Should_Propagate_To_Children ( )
{
// Issue #20845 (comment): Putting the DataContext binding on the TabItem itself
// is also broken. The child should inherit the TabItem's DataContext.
using var app = UnitTestApplication . Start ( TestServices . StyledWindow ) ;
var viewModel = new MainViewModel ( ) ;
var textBlock = new TextBlock ( ) ;
textBlock . Bind ( TextBlock . TextProperty , new Binding ( "Name" ) ) ;
var tab1View = new UserControl { Content = textBlock } ;
var target = new TabControl
{
Template = TabControlTemplate ( ) ,
DataContext = viewModel ,
Items =
{
new TabItem
{
Header = "Tab1" ,
[~TabItem.DataContextProperty] = new Binding ( "Tab1" ) ,
Content = tab1View ,
} ,
} ,
} ;
var root = new TestRoot ( target ) ;
Prepare ( target ) ;
// The TabItem's DataContext should be the Tab1ViewModel.
var tabItem = ( TabItem ) target . Items [ 0 ] ! ;
Assert . Same ( viewModel . Tab1 , tabItem . DataContext ) ;
// The UserControl should inherit the TabItem's DataContext.
Assert . Same ( viewModel . Tab1 , tab1View . DataContext ) ;
// The TextBlock should display the Name from Tab1ViewModel.
Assert . Equal ( "Tab 1 message here" , textBlock . Text ) ;
}
[Fact]
public void Switching_Tabs_Should_Not_Null_Out_DataContext_Bound_Properties ( )
{
// Issue #20845: DataContext binding should survive tab switches.
using var app = UnitTestApplication . Start ( TestServices . StyledWindow ) ;
var viewModel = new MainViewModel ( ) ;
var tab1View = new UserControl ( ) ;
tab1View . Bind ( UserControl . DataContextProperty , new Binding ( "Tab1" ) ) ;
var textBlock = new TextBlock ( ) ;
textBlock . Bind ( TextBlock . TextProperty , new Binding ( "Name" ) ) ;
tab1View . Content = textBlock ;
var target = new TabControl
{
Template = TabControlTemplate ( ) ,
DataContext = viewModel ,
Items =
{
new TabItem
{
Header = "Tab1" ,
Content = tab1View ,
} ,
new TabItem
{
Header = "Tab2" ,
Content = "Other content" ,
} ,
} ,
} ;
var root = new TestRoot ( target ) ;
Prepare ( target ) ;
Assert . Same ( viewModel . Tab1 , tab1View . DataContext ) ;
Assert . Equal ( "Tab 1 message here" , textBlock . Text ) ;
// Switch to tab 2 and back
target . SelectedIndex = 1 ;
target . SelectedIndex = 0 ;
// DataContext binding should still be resolved correctly.
Assert . Same ( viewModel . Tab1 , tab1View . DataContext ) ;
Assert . Equal ( "Tab 1 message here" , textBlock . Text ) ;
}
[Fact]
public void Content_Should_Not_Temporarily_Get_Wrong_DataContext_When_Switching_Tabs ( )
{
// When ContentPart.Content is set, ContentPresenter.UpdateChild clears its
// DataContext before we can set it to the container's DataContext. This causes
// the content to briefly inherit TabControl's DataContext instead of TabItem's.
using var app = UnitTestApplication . Start ( TestServices . StyledWindow ) ;
var viewModel = new MainViewModel ( ) ;
var tab1View = new UserControl ( ) ;
var tab2View = new UserControl ( ) ;
var target = new TabControl
{
Template = TabControlTemplate ( ) ,
DataContext = viewModel ,
Items =
{
new TabItem
{
Header = "Tab1" ,
[~TabItem.DataContextProperty] = new Binding ( "Tab1" ) ,
Content = tab1View ,
} ,
new TabItem
{
Header = "Tab2" ,
[~TabItem.DataContextProperty] = new Binding ( "Tab2" ) ,
Content = tab2View ,
} ,
} ,
} ;
var root = new TestRoot ( target ) ;
Prepare ( target ) ;
Assert . Same ( viewModel . Tab1 , tab1View . DataContext ) ;
// Track all DataContext values the new content receives during the switch.
var dataContexts = new List < object? > ( ) ;
tab2View . PropertyChanged + = ( s , e ) = >
{
if ( e . Property = = StyledElement . DataContextProperty )
dataContexts . Add ( e . NewValue ) ;
} ;
target . SelectedIndex = 1 ;
// tab2View should only have received the correct DataContext (Tab2ViewModel).
// It should NOT have temporarily received the TabControl's DataContext (MainViewModel).
Assert . All ( dataContexts , dc = > Assert . Same ( viewModel . Tab2 , dc ) ) ;
Assert . Same ( viewModel . Tab2 , tab2View . DataContext ) ;
}
[Fact]
public void Transition_Should_Not_Apply_New_DataContext_To_Old_Content ( )
{
// When a PageTransition is set, the old content stays in ContentPart while the
// new content goes into _contentPresenter2. The DataContext subscription for the
// new container should not update ContentPart's DataContext (which still holds
// the old content).
using var app = Start ( ) ;
var viewModel = new MainViewModel ( ) ;
var tab1View = new UserControl ( ) ;
var tab2View = new UserControl ( ) ;
var transition = new Mock < IPageTransition > ( ) ;
transition
. Setup ( t = > t . Start (
It . IsAny < Visual ? > ( ) , It . IsAny < Visual ? > ( ) ,
It . IsAny < bool > ( ) , It . IsAny < CancellationToken > ( ) ) )
. Returns ( Task . CompletedTask ) ;
var target = new TabControl
{
PageTransition = transition . Object ,
DataContext = viewModel ,
Items =
{
new TabItem
{
Header = "Tab1" ,
[~TabItem.DataContextProperty] = new Binding ( "Tab1" ) ,
Content = tab1View ,
} ,
new TabItem
{
Header = "Tab2" ,
[~TabItem.DataContextProperty] = new Binding ( "Tab2" ) ,
Content = tab2View ,
} ,
} ,
} ;
var root = CreateRoot ( target ) ;
root . LayoutManager . ExecuteInitialLayoutPass ( ) ;
Assert . Same ( viewModel . Tab1 , tab1View . DataContext ) ;
// Track all DataContext values the OLD content receives during the transition.
var oldContentDataContexts = new List < object? > ( ) ;
tab1View . PropertyChanged + = ( s , e ) = >
{
if ( e . Property = = StyledElement . DataContextProperty )
oldContentDataContexts . Add ( e . NewValue ) ;
} ;
// Switch tab — triggers transition
target . SelectedIndex = 1 ;
root . LayoutManager . ExecuteLayoutPass ( ) ;
// The old content (tab1View) should NOT have received Tab2's DataContext.
Assert . DoesNotContain ( viewModel . Tab2 , oldContentDataContexts ) ;
}
[Fact]
public void ContentTemplate_With_Control_Content_Should_Set_DataContext_To_Content ( )
{
// When a TabItem has a ContentTemplate and its Content is a Control, the
// ContentPresenter should set DataContext = content (so the template can bind
// to the control's properties), not the TabItem's DataContext.
using var app = UnitTestApplication . Start ( TestServices . StyledWindow ) ;
var viewModel = new MainViewModel ( ) ;
var userControl = new UserControl { Tag = "my-content" } ;
TextBlock ? templateChild = null ;
var contentTemplate = new FuncDataTemplate < UserControl > ( ( x , _ ) = >
{
templateChild = new TextBlock ( ) ;
templateChild . Bind ( TextBlock . TextProperty , new Binding ( "Tag" ) ) ;
return templateChild ;
} ) ;
var target = new TabControl
{
Template = TabControlTemplate ( ) ,
DataContext = viewModel ,
Items =
{
new TabItem
{
Header = "Tab1" ,
[~TabItem.DataContextProperty] = new Binding ( "Tab1" ) ,
ContentTemplate = contentTemplate ,
Content = userControl ,
} ,
} ,
} ;
var root = new TestRoot ( target ) ;
Prepare ( target ) ;
// The ContentPresenter's DataContext should be the content (UserControl),
// not the TabItem's DataContext (Tab1ViewModel), because ContentTemplate is set.
Assert . Same ( userControl , target . ContentPart ! . DataContext ) ;
Assert . NotNull ( templateChild ) ;
Assert . Equal ( "my-content" , templateChild ! . Text ) ;
}
[Fact]
public void ContentTemplate_With_Control_Content_Should_Set_DataContext_To_Content_After_Tab_Switch ( )
{
// Same as above but verifies the behavior after switching tabs.
using var app = UnitTestApplication . Start ( TestServices . StyledWindow ) ;
var viewModel = new MainViewModel ( ) ;
var userControl = new UserControl { Tag = "my-content" } ;
TextBlock ? templateChild = null ;
var contentTemplate = new FuncDataTemplate < UserControl > ( ( x , _ ) = >
{
templateChild = new TextBlock ( ) ;
templateChild . Bind ( TextBlock . TextProperty , new Binding ( "Tag" ) ) ;
return templateChild ;
} ) ;
var target = new TabControl
{
Template = TabControlTemplate ( ) ,
DataContext = viewModel ,
Items =
{
new TabItem
{
Header = "Tab1" ,
[~TabItem.DataContextProperty] = new Binding ( "Tab1" ) ,
ContentTemplate = contentTemplate ,
Content = userControl ,
} ,
new TabItem
{
Header = "Tab2" ,
Content = "Other content" ,
} ,
} ,
} ;
var root = new TestRoot ( target ) ;
Prepare ( target ) ;
Assert . Same ( userControl , target . ContentPart ! . DataContext ) ;
// Switch away and back.
target . SelectedIndex = 1 ;
target . SelectedIndex = 0 ;
// DataContext should still be the content, not the TabItem's DataContext.
Assert . Same ( userControl , target . ContentPart ! . DataContext ) ;
Assert . NotNull ( templateChild ) ;
Assert . Equal ( "my-content" , templateChild ! . Text ) ;
}
private class TabDataContextViewModel : NotifyingBase
{
private string? _ selectedItem ;
public string? SelectedItem
{
get = > _ selectedItem ;
set = > SetField ( ref _ selectedItem , value ) ;
}
}
private class MainViewModel
{
public Tab1ViewModel Tab1 { get ; set ; } = new ( ) ;
public Tab2ViewModel Tab2 { get ; set ; } = new ( ) ;
}
private class Tab1ViewModel
{
public string Name { get ; set ; } = "Tab 1 message here" ;
}
private class Tab2ViewModel
{
public string Name { get ; set ; } = "Tab 2 message here" ;
}
private class Item
{
public Item ( string value )
Steven Kirk
2 weeks ago
GitHub