We Keep Coding

How to focus on an element after button click

I'm relatively new to WPF and I am struggling to manage the focus of an element at runtime.
I have a simple user control with a TextBox inside
<UserControl [...]
IsVisibleChanged="UserControl_IsVisibleChanged">
[...]
<TextBox x:Name="myTextBox" [...] />
</UserControl>
That I added on my WPF window
<ctrl:MyPanel
x:Name="myPanel"
Visibility="{Binding MyBooleanProperty}"
Panel.ZIndex="999" />
MyBooleanProperty is changing at runtime under some logic and the panel is showing up accordingly.
I need to have keyboard focus on myTextBox everytime myPanel becomes visible so user can enter data without using mouse, tab key or anything else.
Here's the logic on the event handler of IsVisibleChanged
private void UserControl_IsVisibleChanged(object sender, DependencyPropertyChangedEventArgs e)
{
if (this.Visibility == Visibility.Visible)
{
myTextBox.Focus();
myTextBox.SelectAll();
}
}
This works, but if I click any button on the window before myPanel becomes visible then I cannot set focus in myTextBox.
I've tried many things, for example setting
Focusable="False"
on the buttons with no luck.
Thanks in advance for your help!

After a little more searching I found a workaround based on this answer by Rachel:
Dispatcher.BeginInvoke(DispatcherPriority.Input,
new Action(delegate () {
myTextBox.Focus();
Keyboard.Focus(myTextBox);
myTextBox.SelectAll();
}));
Delegating the focus action actually works.

Reusing tab content with DataTemplate

I have a tab control where the tabs are created at runtime. The contents of the tabs will be one of several user controls, each containing hundreds of other controls. As it takes a long time to create these user controls, I'm trying to find a way to reuse them rather than creating a new instance for each tab.
I'm setting the tab page contents using a DataTemplate as follows:
<DataTemplate>
<ScrollViewer Content="{Binding Content}" />
</DataTemplate>
Where Content is the view model for the view I want to show in the tab.
Elsewhere I use data templates to map each view model to a view, e.g.
<DataTemplate DataType="{x:Type vm:MyViewModel1}">
<ctl:CacheContentControl ContentType="{x:Type ctl:MyView1}" />
</DataTemplate>
<DataTemplate DataType="{x:Type vm:MyViewModel2}">
<ctl:CacheContentControl ContentType="{x:Type ctl:MyView2}" />
</DataTemplate>
CacheContentControl is a wrapper around ContentControl that I use for the caching:
public class CacheContentControl : ContentControl
{
private static Dictionary<Type, Control> cache = new Dictionary<Type, Control>();
public CacheContentControl()
{
Unloaded += CacheContentControl_Unloaded;
}
private void CacheContentControl_Unloaded(object sender, RoutedEventArgs e)
{
Content = null;
}
private Type _contentType;
public Type ContentType
{
get { return _contentType; }
set
{
_contentType = value;
Content = GetView(_contentType);
}
}
public Control GetView(Type type)
{
if (!cache.ContainsKey(type))
{
cache.Add(type, (Control)Activator.CreateInstance(type));
}
return cache[type];
}
}
This ensures that the DataTemplate first checks the cache to see if it can reuse a control before creating a new instance.
This works for any new tabs that are created. The first tab is slow as expected since it needs to create the initial control, but all subsequent tabs using the same control load almost immediately. The problem I'm having is that when I click back to a previous tab the control no longer appears and the tab is blank.
I guess this is happening because I can't show the same control instance on the same form multiple times which makes sense. I've been able to work around it by handing the IsVisibleChanged event for my CacheContentControl as follows:
private void CacheContentControl_IsVisibleChanged(object sender, DependencyPropertyChangedEventArgs e)
{
if (IsVisible && ContentType != null)
{
Control ctl = GetView(_contentType);
ctl.DataContext = DataContext;
Content = ctl;
}
else
{
Content = null;
}
}
When a tab loses focus it removes the control, the tab that receives focus can then retrieve the control from the cache which seems to work.
The issue is that the speeds have gone back to being slow again and I'm not sure why. Obviously it's possible to move a control instance from one tab to another without delay as it does this every time I create a new tab. There must be something the DataTemplate does differently to change the control's parent?

I’m not sure that you need to go so far as to cache your user controls as WPF largely does this for you.
The normal approach inside a DataTemplate keyed by type is not to use a ContentControl but simply to have the UserControl as the template.
<DataTemplate x:Key=“MyViewmodelType”>
<MyViewControl />
</DataTemplate>
The TabControl will have a ContentControl which has its Content set to whichever ViewModel is applicable and WPF will automatically render it using the specified DataTemplate for that type and set the DataContext.
I have built massive WPF Views that were rendered using DataTemplates as per the simpler approach outlined above without encountering any serious performance issues and I think that you could safely start developing by simply binding ContentControl.Content to your ViewModel instance and letting WPF handle the rendering using the simpler DataTemplate approach above.

Showing different controls programmatically

In my WPF app, I've to show different controls in the window for different user actions. Like, when user selects an image, I show a Image control and when the user selects a text file, I show a TextBox control. Similarly there are many controls for different user selections.
To do this I'm first doing Visibility = Visibility.Collapsed for all controls using a foreach loop, then doing Visibility = Visibility.Visible for the controls that I've to show.
Is there a more efficient way of doing this? The window flickers and is not really snappy when changing controls as there are many controls.

I always use a ContentControl for this. It produces very clean xaml code and is superfast, I've never seen any flicker even in rather loaded views. It does require any extra frameworks beyond WPF.
<ContentControl Content="{Binding Selected}">
<ContentControl.Resources>
<DataTemplate DataType="{x:Type viewModels:FirstOne}">
<!-- View code for first view goes here -->
<TextBlock>Hi</TextBlock>
</DataTemplate>
<DataTemplate DataType="{x:Type viewModels:SecondOne}">
<!-- View code for second view goes here -->
<Image Source="{Binding Image}" />
</DataTemplate>
</ContentControl.Resources>
</ContentControl>
And then I have a MainViewModel handing the navigation with a property
class MainViewModel: ViewModel, INavigation
{
public ViewModel Selected
{
get { return _selected; }
private set
{
_selected = value;
RaisePropertyChanged();
}
public void Show(ViewModel viewModel) { Selected = viewModel; }
}
}
The INavigation interface is just something like so
interface INavigation { void Show(ViewModel viewModel); }
An example view model
class FirstOne: ViewModel
{
private readonly INavigation _navigation;
public FirstOne(INavigation navigation) { _navigation = navigation; }
public void ButtonClicked()
{
_navigation.Show(new SecondOne());
}
}

First, you may want to avoid doing Visibility=Visibility.Collapsed for controls that you are about to make visible. That could reduce some unnecessary screen activity.
Second, rather than having the user experience all the individual visibility changes in a serial fashion, you might want to keep your controls in a parent control that you can hide before the visibility changes take place and then unhide once the changes are complete. You could even use an opacity animation to fade it out and then back in. Of course, without seeing or understanding more about your app, I can't tell what's really appropriate.

Windows Store 8.1. XAML Progress Bar between pages

I am having a problem with a page in my Windows 8.1 Store App that is taking a long time to render - it is a grid with a number of columns and rows that gets bound to data on loading of the page.
It is not the loading of the data that is slow but the actual binding of the data to the grid.
I ideally want to display a dialog bar to indicate to the user that something is loading and they have clicked on the previous navigate button okay.
I saw someone mention the possibility of having a "loading page" which only has a progress bar in it - and I thought this solution might work but I can't work out in what event of the loading page should I navigate to the actual page.
i.e.
User clicks button which calls
this.Frame.Navigate(typeof(LoadingPage));
Loading Page displays a progress bar
I know need to be able to call
this.Frame.Navigate(typeof(ActualPage));
The user sees the progress bar whilst ActualPage loads.
Any suggestions would be greatly appreciated thanks!

Thanks to the support team at DEVExpress I have a solution to my problem.
Firstly on the page that takes time to load I have wrapped my Grid in a ContentControl
<ContentControl Visibility="Collapsed" Name="Content">
<!-- Grid in here -->
</ContentControl>
I then added a TextBlock which I will use as to display "Loading..." to my page. I have called this control indicator.
<TextBlock x:Name="indicator" Text="Loading..." />
I have attached the following method to the Loaded event of the page which uses a timer
void MainPage_Loaded(object sender, RoutedEventArgs e)
{
indicator.Visibility = Windows.UI.Xaml.Visibility.Visible;
DispatcherTimer t = new DispatcherTimer { Interval = TimeSpan.FromSeconds(1) };
t.Tick += (dd, ee) =>
{
t.Stop();
Content.Visibility = Windows.UI.Xaml.Visibility.Visible;
};
t.Start();
}
Then when the gridcontrol has Loaded I hide the indicator TextBlock
void gridControl_Loaded(object sender, RoutedEventArgs e)
{
indicator.Visibility = Windows.UI.Xaml.Visibility.Collapsed;
}
This works perfectly for me. I can't use the Windows 8 ProgressBar control because the animation is loaded on the same thread that loads the grid - but I am happy enough to have any indicator.
Also thanks Brian Stump for pointing me in the right direction.

First, I will suggest using a ListView or GridView to display your databound objects because of build-in UI virtualization.
However, maybe this will work for your situation.
Do you know when your page is ready to display? If so, place a progress ring in front of your grid while it loads in the background.
<Grid x:Name="FullPageGrid">
<Grid x:Name="YourGridContent">
</Grid>
<Grid Background="White" Visibility="Visible" x:Name="ProgressRingGrid">
<ProgressRing IsActive="True"></ProgressRing>
</Grid>
</Grid>
When the data is fully loaded, change the visibility of the "ProgressRingGrid" to Visibility="Collapsed"

Toolbar Overlay over WindowsFormsHost

I have a SWF object embedded in a WindowsFormsHost Control inside a WPF window.
I'd like to add a toolbar over the swf movie.
The problem with the snippet of code I have below, is that when the new child is added to the host control (or the movie is loaded, I haven't figured out which yet), the toolbar is effectively invisible. It seems like the z-index of the swf is for some reason set to the top.
Here is what it looks like:
XAML:
<Grid Name="Player">
<WindowsFormsHost Name="host" Panel.ZIndex="0" />
<Grid Name="toolbar" Panel.ZIndex="1" Height="50"
VerticalAlignment="Bottom">
[play, pause, seek columns go here]
</Grid>
</Grid>
C#:
private void Window_Loaded(object sender, RoutedEventArgs e)
{
flash = new AxShockwaveFlashObjects.AxShockwaveFlash();
host.Child = flash;
flash.LoadMovie(0, [movie]); // Movie plays, but no toolbar :(
}
Any insight on this issue would be much appreciated.
Update: Since no suitable answer was posted, I've placed my own solution below. I realize this is more of a hack than a solution so I'm open to other suggestions.

Here is my hackaround the WindowsFormsHost Z-index issue.
The idea is to place whatever you need to be overlayed nested inside a Popup. Then to update that popup's position as per this answer whenever the window is resized/moved.
Note: You'll probably also want to handle events when the window becomes activated/deactivated, so the pop disappears when the window goes out of focus (or behind another window).
XAML:
<Window [stuff]
LocationChanged="Window_LocationChanged"
SizeChanged="Window_SizeChanged" >
<Grid Name="Player">
[same code as before]
<Popup Name="toolbar_popup" IsOpen="True" PlacementTarget="{Binding ElementName=host}">
[toolbar grid goes here]
</Popup>
</Grid>
</Window>
C#:
private void resetPopup()
{
// Update position
// https://stackoverflow.com/a/2466030/865883
var offset = toolbar_popup.HorizontalOffset;
toolbar_popup.HorizontalOffset = offset + 1;
toolbar_popup.HorizontalOffset = offset;
// Resizing
toolbar_popup.Width = Player.ActualWidth;
toolbar_popup.PlacementRectangle = new Rect(0, host.ActualHeight, 0, 0);
toolbar_popup.Placement = System.Windows.Controls.Primitives.PlacementMode.Top;
}
private void Window_LocationChanged(object sender, EventArgs e)
{ resetPopup(); }
private void Window_SizeChanged(object sender, SizeChangedEventArgs e)
{ resetPopup(); }

Another solution I've discovered is to use Windows Forms' ElementHost control. Since I'm using a Windows Form inside a WPF window anyway, why not just use an entire Windows Form and save myself Z-Issue headaches.
The ElementHost control is really useful, because I can still use my toolbar UserControl, and embed it inside the Windows Form. I've discovered that adding a child can be finicky with Windows Forms, so here's a snippet describing the solution:
First, toss in the ActiveX object, then an ElementHost Control, using the designer.
Form1.Designer.cs:
private AxShockwaveFlashObjects.AxShockwaveFlash flash;
private System.Windows.Forms.Integration.ElementHost elementHost1;
Form1.cs
public Form1(string source)
{
InitializeComponent();
toolbar = new UserControl1();
this.elementHost1.Child = this.toolbar;
this.flash.LoadMovie(0, source);
}
Note that the child was not set in the designer. I found that for more complex UserControls the designer will complain (though nothing happens at runtime).
This solution is, of course, still not entirely ideal, but it provides the best of both worlds: I can still code my UserControls in XAML, but now I don't have to worry about Z-indexing issues.