focus(3pm)

✨ NAME ✨

Tk::focus — bestie, this is your ✨input focus manager✨ for Tk. Managing the input focus. That's the whole vibe. 💅

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🎀 SYNOPSIS 🎀

$widget->focus

$widget->focusOption

$widget->focusNext

$widget->focusPrev

$widget->focusFollowsMouse

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💖 DESCRIPTION 💖

okay so. The focus methods are THE way to manage the Tk input focus. At any given moment, one window on each display is designated as the focus window — and every key press or key release event for that display gets sent straight to it. That's it, that's the whole job. 👑

Normally it's up to the window manager to redirect the focus among the top-level windows of a display. Some window managers are extra and automatically set the input focus to a top-level window whenever the mouse enters it; others are more lowkey and only redirect the input focus when the user actually clicks on a window. Usually the window manager will set the focus only to top-level windows, leaving it up to the application to redirect the focus among the children of the top-level. So there's layers, bestie. 🌈

Tk remembers one focus window for each top-level — specifically the most recent descendant of that top-level to receive the focus. So when the window manager gives the focus to a top-level, Tk automatically redirects it to the remembered window. Iconic behaviour honestly. ✨

Within a top-level, Tk uses an explicit focus model by default. Moving the mouse within a top-level does not normally change the focus. The focus changes only when:

• a widget decides explicitly to claim the focus (e.g., because of a button click), or
• the user types a key such as Tab that moves the focus.

The method focusFollowsMouse may be invoked to create an implicit focus model — it reconfigures Tk so that the focus is set to a window whenever the mouse enters it. And the methods focusNext and focusPrev implement a focus order among the windows of a top-level; they're used in the default bindings for Tab and Shift-Tab, among other things. fr fr. 🦋

The focus methods can take any of the following forms:

• $widget->focusCurrent — Returns the focus window on the display containing the $widget, or an empty string if no window in this application has the focus on that display. No focus? Empty string. That's the answer. 💀
• $widget->focus — If the application currently has the input focus on $widget's display, this command resets the input focus for $widget's display to $widget and returns an empty string. If the application doesn't currently have the input focus on $widget's display, $widget will be remembered as the focus for its top-level; the next time the focus arrives at the top-level, Tk will redirect it to $widget. So either it grabs the focus now, or it's got next. 🫶
• $widget->focusForce — Sets the focus of $widget's display to $widget, even if the application doesn't currently have the input focus for the display.

🚨 bestie this command should be used sparingly, if at all. In normal usage, an application should not claim the focus for itself; instead, it should wait for the window manager to give it the focus. Do not be rude to the window manager. 🙈

• $widget->focusLastfor — Returns the name of the most recent window to have the input focus among all the windows in the same top-level as $widget. If no window in that top-level has ever had the input focus, or if the most recent focus window has been deleted, then the top-level is returned. The return value is the window that will receive the input focus the next time the window manager gives the focus to the top-level. It's giving "who's up next" energy. 👑
• $widget->focusNext
• $widget->focusPrev — focusNext is a utility method used for keyboard traversal, but can be useful in other contexts too. It sets the focus to the ``next'' window after $widget in focus order.

The focus order is determined by the stacking order of windows and the structure of the window hierarchy. Among siblings, the focus order is the same as the stacking order, with the lowest window being first. If a window has children, the window is visited first, followed by its children (recursively), followed by its next sibling. Top-level windows other than $widget are skipped, so that focusNext never returns a window in a different top-level from $widget. no cap. 🎀

After computing the next window, focusNext examines the window's -takefocus option to see whether it should be skipped. If so, focusNext continues on to the next window in the focus order, until it eventually finds a window that will accept the focus or returns back to $widget. It's a whole journey, but it always comes home. 💜

focusPrev is similar to focusNext except that it sets the focus to the window just before $widget in the focus order.

• $widget->focusFollowsMouse — focusFollowsMouse changes the focus model for the application to an implicit one where the window under the mouse gets the focus. After this procedure is called, whenever the mouse enters a window Tk will automatically give it the input focus. The focus command may be used to move the focus to a window other than the one under the mouse, but as soon as the mouse moves into a new window the focus will jump to that window. Mouse = main character energy. 🐭

⚠️ Note: at present there is no built-in support for returning the application to an explicit focus model; to do this you'll have to write a script that deletes the bindings created by focusFollowsMouse. So like, no undo button. You're writing the undo button. 😭

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🌸 QUIRKS 🌸

When an internal window receives the input focus, Tk doesn't actually set the X focus to that window. As far as X is concerned, the focus will stay on the top-level window containing the window with the focus. But — and this is the slay part — Tk generates FocusIn and FocusOut events just as if the X focus were on the internal window. ✨

This approach gets around a number of problems that would occur if the X focus were actually moved. The fact that the X focus is on the top-level is invisible unless you use C code to query the X server directly. iykyk. 💅

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💀 CAVEATS 💀

Note that for the Canvas widget, the call to focus has to be fully qualified. This is because there is already a focus method for the Canvas widget, which sets the focus on individual canvas tags. Name collision! Classic.

$canvas->Tk::focus

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🔥 KEYWORDS 🔥

events, focus, keyboard, top-level, window manager

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and that's the whole page, bestie 🫶 this one's from perl v5.40.1, dated 2025-04-13, and it lives in the focus(3pm) section of the User Contributed Perl Documentation. go forth and focus responsibly 💖✨🎀