Can't set focus to a child of UserControl

问题

I have a UserControl which contains a TextBox. When my main window loads I want to set the focus to this textbox so I added Focusable="True" GotFocus="UC_GotFocus" to the UserControls definition and FocusManager.FocusedElement="{Binding ElementName=login}" to my main windows definition. In the UC_GotFocus method i simply call .Focus() on the control i want to focus on but this doesn't work.

All i need to do is have a TextBox in a UserControl receive focus when the application starts.

Any help would be appreciated, thanks.

回答1:

I recently fixed this problem for a login splash screen that is being displayed via a storyboard when the main window is first loaded.

I believe there were two keys to the fix. One was to make the containing element a focus scope. The other was to handle the Storyboard Completed event for the storyboard that was triggered by the window being loaded.

This storyboard makes the username and password canvas visible and then fades into being 100% opaque. The key is that the username control was not visible until the storyboard ran and therefore that control could not get keyboard focus until it was visible. What threw me off for awhile was that it had "focus" (i.e. focus was true, but as it turns out this was only logical focus) and I did not know that WPF had the concept of both logical and keyboard focus until reading Kent Boogaart's answer and looking at Microsoft's WPF link text

Once I did that the solution for my particular problem was straightforward:

1) Make the containing element a focus scope

<Canvas FocusManager.IsFocusScope="True" Visibility="Collapsed">
    <TextBox x:Name="m_uxUsername" AcceptsTab="False" AcceptsReturn="False">
    </TextBox>
</Canvas>

2) Attach a Completed Event Handler to the Storyboard

    <Storyboard x:Key="Splash Screen" Completed="UserNamePassword_Storyboard_Completed">
...
</Storyboard>

and

3) Set my username TextBox to have the keyboard focus in the storyboard completed event handler.

void UserNamePassword_Storyboard_Completed(object sender, EventArgs e)
{
 m_uxUsername.Focus();
}

Note that calling item.Focus() results in the call Keyboard.Focus(this), so you don't need to call this explicitly. See this question about the difference between Keyboard.Focus(item) and item.Focus.

回答2:

Its stupid but it works:

Pop a thread that waits a while then comes back and sets the focus you want. It even works within the context of an element host.

private void ListView_SelectionChanged(object sender, SelectionChangedEventArgs e)
{

 System.Threading.ThreadPool.QueueUserWorkItem(
                   (a) =>
                        {
                            System.Threading.Thread.Sleep(100);
                            someUiElementThatWantsFocus.Dispatcher.Invoke(
                            new Action(() =>
                            {
                                someUiElementThatWantsFocus.Focus();

                            }));
                        }
                   );

}

回答3:

Just recently I had a list-box that housed some TextBlocks. I wanted to be able to double click on the text block and have it turn into a TextBox, then focus on it and select all the text so the user could just start typing the new name (Akin to Adobe Layers)

Anyway, I was doing this with an event and it just wasn't working. The magic bullet for me here was making sure that I set the event to handled. I figure it was setting focus, but as soon as the event went down the path it was switching the logical focus.

The moral of the story is, make sure you're marking the event as handled, that might be your issue.

回答4:

“When setting initial focus at application startup, the element to receive focus must be connected to a PresentationSource and the element must have Focusable and IsVisible set to true. The recommended place to set initial focus is in the Loaded event handler" (MSDN)

Simply add a "Loaded" event handler in the constructor of your Window (or Control), and in that event handler call the Focus() method on the target control.

    public MyWindow() {
        InitializeComponent();
        this.Loaded += new RoutedEventHandler(MyWindow_Loaded);
    }

    void MyWindow_Loaded(object sender, RoutedEventArgs e) {
        textBox.Focus();
    }

回答5:

since i tried a fuzquat's solution and found it the most generic one, i thought i'd share a different version, since some complained about it looking messy. so here it is:

                casted.Dispatcher.BeginInvoke(new Action<UIElement>(x =>
                {
                    x.Focus();
                }), DispatcherPriority.ApplicationIdle, casted);

no Thread.Sleep, no ThreadPool. Clean enough i hope. Could really use some rep so i can comment on other peoples solutions.

UPDATE:

Since people seem to like pretty code:

public static class WpfExtensions
{
    public static void BeginInvoke<T>(this T element, Action<T> action, DispatcherPriority priority = DispatcherPriority.ApplicationIdle) where T : UIElement
    {
        element.Dispatcher.BeginInvoke(priority, action);
    }
}

now you can call it like this:

child.BeginInvoke(d => d.Focus());

回答6:

Set your user control to Focusable="True" (XAML)
Handle the GotFocus event on your control and call yourTextBox.Focus()
Handle the Loaded event on your window and call yourControl.Focus()

I have a sample app running with this solution as I type. If this does not work for you, there must be something specific to your app or environment that causes the problem. In your original question, I think the binding is causing the problem. I hope this helps.

回答7:

WPF supports two different flavors of focus:

Keyboard focus
Logical focus

The FocusedElement property gets or sets logical focus within a focus scope. I suspect your TextBox does have logical focus, but its containing focus scope is not the active focus scope. Ergo, it does not have keyboard focus.

So the question is, do you have multiple focus scopes in your visual tree?

回答8:

I found a good series of blog posts on WPF focus.

Part 1: It’s Basically Focus
Part 2: Changing WPF focus in code
Part 3: Shifting focus to the first available element in WPF

They are all good to read, but the 3rd part specifically deals with setting focus to a UI element in a UserControl.

回答9:

I've noticed a focus issue specifically related to hosting WPF UserControls within ElementHosts which are contained within a Form that is set as an MDI child via the MdiParent property.

I'm not sure if this is the same issue others are experiencing but you dig into the details by following the link below.

Issue with setting focus within a WPF UserControl hosted within an ElementHost in a WindowsForms child MDI form

回答10:

After having a 'WPF Initial Focus Nightmare' and based on some answers on stack, the following proved for me to be the best solution.

First, add your App.xaml OnStartup() the followings:

EventManager.RegisterClassHandler(typeof(Window), Window.LoadedEvent,
          new RoutedEventHandler(WindowLoaded));

Then add the 'WindowLoaded' event also in App.xaml :

void WindowLoaded(object sender, RoutedEventArgs e)
    {
        var window = e.Source as Window;
        System.Threading.Thread.Sleep(100);
        window.Dispatcher.Invoke(
        new Action(() =>
        {
            window.MoveFocus(new TraversalRequest(FocusNavigationDirection.First));

        }));
    }

The threading issue must be use as WPF initial focus mostly fails due to some framework race conditions.

I found the following solution best as it is used globally for the whole app.

Hope it helps...

Oran

回答11:

What did the trick for me was the FocusManager.FocusedElement attribute. I first tried to set it on the UserControl, but it didn't work.

So I tried putting it on the UserControl's first child instead:

<UserControl x:Class="WpfApplication3.UserControl1"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Grid FocusManager.FocusedElement="{Binding ElementName=MyTextBox, Mode=OneWay}">
    <TextBox x:Name="MyTextBox"/>
</Grid>

... and it worked! :)

回答12:

I converted fuzquat's answer to an extension method. I'm using this instead of Focus() where Focus() did not work.

using System;
using System.Threading;
using System.Windows;

namespace YourProject.Extensions
{
    public static class UIElementExtension
    {
        public static void WaitAndFocus(this UIElement element, int ms = 100)
        {
            ThreadPool.QueueUserWorkItem(f =>
            {
                Thread.Sleep(ms);

                element.Dispatcher.Invoke(new Action(() =>
                {
                    element.Focus();
                }));
            });
        }
    }
}

回答13:

I have user control - stack panel with two text boxes.The text boxes were added in contructor, not in the xaml. When i try to focus first text box, nothing happend. The siggestion with Loaded event fix my problem. Just called control.Focus() in Loaded event and everthing.

回答14:

Assuming you want to set focus for Username textbox, thus user can type in directly every time it shows up.

In Constructor of your control:

this.Loaded += (sender, e) => Keyboard.Focus(txtUsername);

回答15:

After trying combinations of the suggestions above, I was able to reliably assign focus to a desired text box on a child UserControl with the following. Basically, give focus to the child control and have the child UserControl give focus to its TextBox. The TextBox's focus statement returned true by itself, however did not yield the desired result until the UserControl was given focus as well. I should also note that the UserControl was unable to request focus for itself and had to be given by the Window.

For brevity I left out registering the Loaded events on the Window and UserControl.

Window

private void OnWindowLoaded(object sender, RoutedEventArgs e)
{
    ControlXYZ.Focus();
}

UserControl

private void OnControlLoaded(object sender, RoutedEventArgs e)
{
    TextBoxXYZ.Focus();
}

回答16:

I set it in the PageLoaded() or control loaded, but then I'm calling WCF async service and doing stuff that seems to lose the focus. I have to to set it at the end of all the stuff I do. That's fine and all, but sometimes I make changes to the code and then I forget that I'm also setting the cursor.

回答17:

I don't like solutions with setting another tab scope for UserControl. In that case, you will have two different carets when navigating by keyboard: on the window and the another - inside user control. My solution is simply to redirect focus from user control to inner child control. Set user control focusable (because by default its false):

<UserControl ..... Focusable="True">

and override focus events handlers in code-behind:

protected override void OnGotFocus(RoutedEventArgs e)
{
    base.OnGotFocus(e);
    MyTextBox.Focus();
}

protected override void OnGotKeyboardFocus(KeyboardFocusChangedEventArgs e)
{
    base.OnGotKeyboardFocus(e);
    Keyboard.Focus(MyTextBox);
}

回答18:

I had same problem with setting keyboard focus to canvas in WPF user control. My solution

In XAML set element to Focusable="True"

In element_mousemove event create simple check:

if(!element.IsKeyBoardFocused)
    element.Focus();

In my case it works fine.

来源：https://stackoverflow.com/questions/673536/cant-set-focus-to-a-child-of-usercontrol

标签

wpf

focus

user-controls

focusmanager