Window Events

The window reports what it is doing as ordinary Events under names Dry reserves for itself. They travel on the same bus as any Event of your own, reach both sides, and are subscribed to the same way.

window.dry.on('window:maximized', () => icon.src = RESTORE);
window.dry.on('window:resized', ({ width, height }) => show(width, height));

wv.on('window:resized', lambda size: print(size['width'], size['height']))

The names come in opposed pairs rather than one name carrying a boolean, because a listener should read as the thing that happened rather than unwrap a value before it knows what it was told.

What you can rely on

• Every one of them fires for a change the user made, not only for one your application made: a keyboard shortcut, the window menu, a double-click on the titlebar. The window’s state is read once per turn of the event loop and compared with the last reading, so a change with no platform event of its own is still caught.
• A change your Python made is announced identically. wv.maximized = True and a double-click on the titlebar reach a listener as the same window:maximized, because both are read off the window rather than reported by whoever asked — and a change the platform refused announces nothing. See Runtime window control.
• window:hidden and window:shown are reachable through wv.visible, which is the only thing in Dry that takes a window off the screen without closing it. A minimized window is minimized, not hidden.
• Sizes and positions are logical pixels, the same unit size= and min_size= are given, so they are the numbers CSS is working in.
• window:resized and window:moved are emitted at most once per turn of the event loop, and only when the value actually changed. A drag firing hundreds of platform events a second cannot produce more Events than the window had turns to draw in, so a listener cannot fall behind, and the last turn always carries the final geometry.
• While the window is minimized or hidden, size, position and maximized state hold their last observed values. The platform’s answers there are not about the window the user will see again — Windows parks a minimized window at -32000 — so a minimize does not report a move to nowhere.
• window:close-requested is a notification, not a vote. The close hook is the only thing that can refuse a close.

fullscreen has no Event. wv.fullscreen = True does enter it, but what arrives is what the platform makes of it — on macOS a window:maximized with a window:moved and a window:resized behind it — so a name of its own could not be told from what already comes. Read wv.fullscreen, or wv.state().fullscreen, instead of listening for it.

What is, rather than what changed

An Event only reaches a listener that was registered when it fired. A page that has just loaded, or a callback that was not listening, has observed nothing and still has to draw a maximize button one way round:

const { maximized } = await window.dry.state();

if wv.state().maximized:
    ...

Both answer from the last reading the event loop took — the same reading every Event above was a difference from — so the query and the Events can never disagree. See Runtime window control.

Reserved means reserved

A name beginning with window: belongs to Dry. Listening is unrestricted — that is exactly how these are heard, on both sides — but wv.emit and window.dry.emit refuse to emit one. A listener for window:resized is therefore hearing from the window and nothing else.