WPF Frame in separate thread? - wpf

Question

I have an application where when a person types or selects a listbox there's a portion of the screen that dynamically updates to a new view.
The problem is since WPF runs everything in a single thread the displaying of the view can interfer with typing or navigating making the app less responsive. What i'd like to do is run the view portion in a different thread.
My first thought was to use a window running on a different thread, but more than being something of a hack there's the problem of the window losing focus and being placed behind the mainwindow when the mainwindow is clicked. I could make it topmost but I also need to place other windows in front of it.
So what's the best way to achieve this, can I place the view in a frame and run it in a different thread?

Answer 1

You can load / generate the data in a backround thread and then update the UI using Dispatcher.BeginInvoke.

Answer 2

I would propose you use the Visibility property of this piece of the screen that you want to make appear and use a trigger to set it from Invisible or Collapsed to Visible whenever the user types or selecs. Or you can animate the Opacity property to produce a cool fading effect ;-) I will add some code to illustrate the point.
EDIT: a time consuming backgroundtask, like File operations, can be accomplished using a BackgroundWorker
<Window x:Class="VisibleOnTypingSpike.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">
<StackPanel>
<StackPanel Orientation="Horizontal">
<Label Name="TypingSnooper"
Visibility="{Binding TypingSnooperVisibility}">
You are typing!</Label>
<Label>
<Label.Style>
<Style>
<Setter Property="Label.Opacity" Value="0"/>
<Style.Triggers>
<DataTrigger Binding="{Binding HasListBoxNewSelection}" Value="True">
<DataTrigger.EnterActions>
<BeginStoryboard >
<Storyboard>
<DoubleAnimation From="0" To="1"
Duration="0:0:1"
Storyboard.TargetProperty="Opacity"/>
</Storyboard>
</BeginStoryboard>
</DataTrigger.EnterActions>
<DataTrigger.ExitActions>
<BeginStoryboard >
<Storyboard>
<DoubleAnimation From="1" To="0"
Duration="0:0:1"
Storyboard.TargetProperty="Opacity"/>
</Storyboard>
</BeginStoryboard>
</DataTrigger.ExitActions>
</DataTrigger>
</Style.Triggers>
</Style>
</Label.Style>
You selected!
</Label>
</StackPanel>
<TextBox TextChanged="TextBox_TextChanged"></TextBox>
<ListBox Name="SimpleListBox"
SelectionChanged="SimpleListBox_SelectionChanged">
<ListBoxItem>1</ListBoxItem>
<ListBoxItem>2</ListBoxItem>
</ListBox>
</StackPanel>
using System.Windows;
using System.Windows.Controls;
namespace VisibleOnTypingSpike
{
public partial class Window1 : Window
{
public Visibility TypingSnooperVisibility
{
get { return (Visibility)GetValue(TypingSnooperVisibilityProperty); }
set { SetValue(TypingSnooperVisibilityProperty, value); }
}
public static readonly DependencyProperty TypingSnooperVisibilityProperty =
DependencyProperty.Register("TypingSnooperVisibility",
typeof(Visibility),
typeof(Window1),
new UIPropertyMetadata(System.Windows.Visibility.Collapsed));
public bool HasListBoxNewSelection
{
get { return (bool)GetValue(HasListBoxNewSelectionProperty); }
set { SetValue(HasListBoxNewSelectionProperty, value); }
}
public static readonly DependencyProperty HasListBoxNewSelectionProperty =
DependencyProperty.Register("HasListBoxNewSelection",
typeof(bool),
typeof(Window1),
new UIPropertyMetadata(false));
public Window1()
{
InitializeComponent();
DataContext = this;
}
private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
{
var textbox = (TextBox) sender;
if (textbox.Text.Length > 0) TypingSnooperVisibility = Visibility.Visible;
else TypingSnooperVisibility = Visibility.Hidden;
}
private void SimpleListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
HasListBoxNewSelection = true;
HasListBoxNewSelection = false;
}
}
}