WPF Frame in separate thread?

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;
        }
    }
}