Wpf scrollviewer keep a row fixed on top năm 2024

This is very simple, when the scroll is located at the bottom and the window is shrunk from below then the items do not move up, they stay in same place on the screen, effectively moving the scroll position off the bottom.

However, scrolling to the top and shrinking the window from the top will move the items down, keeping the scroll at the top.

Apparently this is designed like that, but I question this design since the behavior is not symmetric. This makes it more difficult to design a chat window where the scroll sticks to the bottom.

One could argue that the items should stay in place when items are added/removed outside of the view, so it may make sense to design this scroll behavior like that. So we can close the discussion for now, I can try to implement this behavior by looking at the SizeChanged and other events.

To put the horizontal bar on the top, change its Grid.Row to 0 and adjust the row definitions so that the first row is auto. The ScrollContentPresenter goes in row 1.

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• Article
• 03/17/2022

In this article

Content within a user interface is often larger than a computer screen's display area. The ScrollViewer control provides a convenient way to enable scrolling of content in Windows Presentation Foundation (WPF) applications. This topic introduces the ScrollViewer element and provides several usage examples.

There are two predefined elements that enable scrolling in WPF applications: ScrollBar and ScrollViewer. The ScrollViewer control encapsulates horizontal and vertical ScrollBar elements and a content container (such as a Panel element) in order to display other visible elements in a scrollable area. You must build a custom object in order to use the ScrollBar element for content scrolling. However, you can use the ScrollViewer element by itself because it is a composite control that encapsulates ScrollBar functionality.

The ScrollViewer control responds to both mouse and keyboard commands, and defines numerous methods with which to scroll content by predetermined increments. You can use the event to detect a change in a ScrollViewer state.

A ScrollViewer can only have one child, typically a Panel element that can host a Children collection of elements. The Content property defines the sole child of the ScrollViewer.

Physical scrolling is used to scroll content by a predetermined physical increment, typically by a value that is declared in pixels. Logical scrolling is used to scroll to the next item in the logical tree. Physical scrolling is the default scroll behavior for most Panel elements. WPF supports both types of scrolling.

The IScrollInfo Interface

The IScrollInfo interface represents the main scrolling region within a ScrollViewer or derived control. The interface defines scrolling properties and methods that can be implemented by Panel elements that require scrolling by logical unit, rather than by a physical increment. Casting an instance of IScrollInfo to a derived Panel and then using its scrolling methods provides a useful way to scroll to the next logical unit in a child collection, rather than by pixel increment. By default, the ScrollViewer control supports scrolling by physical units.

StackPanel and VirtualizingStackPanel both implement IScrollInfo and natively support logical scrolling. For layout controls that natively support logical scrolling, you can still achieve physical scrolling by wrapping the host Panel element in a ScrollViewer and setting the CanContentScroll property to false.

The following code example demonstrates how to cast an instance of IScrollInfo to a StackPanel and use content scrolling methods (LineUp and LineDown) defined by the interface.

private void spLineUp(object sender, RoutedEventArgs e)
{
    ((IScrollInfo)sp1).LineUp();
}
private void spLineDown(object sender, RoutedEventArgs e)
{
    ((IScrollInfo)sp1).LineDown();
}

Private Sub spLineUp(ByVal sender As Object, ByVal args As RoutedEventArgs)
    CType(sp1, IScrollInfo).LineUp()
End Sub
Private Sub spLineDown(ByVal sender As Object, ByVal args As RoutedEventArgs)
    CType(sp1, IScrollInfo).LineDown()
End Sub

The following example creates a ScrollViewer in a window that contains some text and a rectangle. ScrollBar elements appear only when they are necessary. When you resize the window, the ScrollBar elements appear and disappear, due to updated values of the ComputedHorizontalScrollBarVisibility and ComputedVerticalScrollBarVisibility properties.

// Create the application's main window
mainWindow = gcnew System::Windows::Window();
mainWindow->Title = "ScrollViewer Sample";
// Define a ScrollViewer
myScrollViewer = gcnew ScrollViewer();
myScrollViewer->HorizontalScrollBarVisibility = ScrollBarVisibility::Auto;
// Add Layout control
myStackPanel = gcnew StackPanel();
myStackPanel->HorizontalAlignment = HorizontalAlignment::Left;
myStackPanel->VerticalAlignment = VerticalAlignment::Top;
TextBlock^ myTextBlock = gcnew TextBlock();
myTextBlock->TextWrapping = TextWrapping::Wrap;
myTextBlock->Margin = System::Windows::Thickness(0, 0, 0, 20);
myTextBlock->Text = "Scrolling is enabled when it is necessary. Resize the Window, making it larger and smaller.";
Rectangle^ myRectangle = gcnew Rectangle();
myRectangle->Fill = Brushes::Red;
myRectangle->Width = 500;
myRectangle->Height = 500;
// Add child elements to the parent StackPanel
myStackPanel->Children->Add(myTextBlock);
myStackPanel->Children->Add(myRectangle);
// Add the StackPanel as the lone child of the ScrollViewer
myScrollViewer->Content = myStackPanel;
// Add the ScrollViewer as the Content of the parent Window object
mainWindow->Content = myScrollViewer;
mainWindow->Show();

// Create the application's main window
mainWindow = new Window ();
mainWindow.Title = "ScrollViewer Sample";
// Define a ScrollViewer
myScrollViewer = new ScrollViewer();
myScrollViewer.HorizontalScrollBarVisibility = ScrollBarVisibility.Auto;
// Add Layout control
myStackPanel = new StackPanel();
myStackPanel.HorizontalAlignment = HorizontalAlignment.Left;
myStackPanel.VerticalAlignment = VerticalAlignment.Top;
TextBlock myTextBlock = new TextBlock();
myTextBlock.TextWrapping = TextWrapping.Wrap;
myTextBlock.Margin = new Thickness(0, 0, 0, 20);
myTextBlock.Text = "Scrolling is enabled when it is necessary. Resize the Window, making it larger and smaller.";
Rectangle myRectangle = new Rectangle();
myRectangle.Fill = Brushes.Red;
myRectangle.Width = 500;
myRectangle.Height = 500;
// Add child elements to the parent StackPanel
myStackPanel.Children.Add(myTextBlock);
myStackPanel.Children.Add(myRectangle);
// Add the StackPanel as the lone child of the ScrollViewer
myScrollViewer.Content = myStackPanel;
// Add the ScrollViewer as the Content of the parent Window object
mainWindow.Content = myScrollViewer;
mainWindow.Show ();

'Define a ScrollViewer.
Dim myScrollViewer As New ScrollViewer
myScrollViewer.HorizontalScrollBarVisibility = ScrollBarVisibility.Auto
'Add Layout control.
Dim myStackPanel As New StackPanel
myStackPanel.HorizontalAlignment = System.Windows.HorizontalAlignment.Left
myStackPanel.VerticalAlignment = System.Windows.VerticalAlignment.Top
Dim myTextBlock As New TextBlock
myTextBlock.TextWrapping = TextWrapping.Wrap
myTextBlock.Margin = New Thickness(0, 0, 0, 20)
myTextBlock.Text = "Scrolling is enabled when it is necessary. Resize the Window, making it larger and smaller."
Dim myRectangle As New Rectangle
myRectangle.Fill = Brushes.Red
myRectangle.Width = 500
myRectangle.Height = 500
'Add child elements to the parent StackPanel.
myStackPanel.Children.Add(myTextBlock)
myStackPanel.Children.Add(myRectangle)
'Add the StackPanel as the lone child of the ScrollViewer
myScrollViewer.Content = myStackPanel
'Add the ScrollViewer as the Content of the parent Window object
Me.Content = myScrollViewer

  
    
      Scrolling is enabled when it is necessary. 
      Resize the window, making it larger and smaller.
      
    
  

Like all controls in Windows Presentation Foundation, the ScrollViewer can be styled in order to change the default rendering behavior of the control. For additional information on control styling, see Styling and Templating.

Paginating Documents

For document content, an alternative to scrolling is to choose a document container that supports pagination. FlowDocument is for documents that are designed to be hosted within a viewing control, such as FlowDocumentPageViewer, that supports paginating content across multiple pages, preventing the need for scrolling. DocumentViewer provides a solution for viewing FixedDocument content, which uses traditional scrolling to display content outside the realm of the display area.

For additional information about document formats and presentation options, see Documents in WPF.

See also

• ScrollViewer
• ScrollBar
• IScrollInfo
• How to: Create a Scroll Viewer
• Documents in WPF
• ScrollBar Styles and Templates
• Controls

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