edifice.use_effect

edifice.use_effect(setup, dependencies=None)

Side-effect Hook inside a @component function.

Behaves like React useEffect.

Parameters:

• setup (Callable[[], Callable[[], None] | None]) – An effect setup function which returns a cleanup function or None.

• dependencies (Optional[Any]) –

  The effect setup function will be called when the dependencies are not __eq__ to the old dependencies.

  If the dependencies are None, then the effect setup function will always be called.

Return type:

None

Returns:

None

The setup function will be called after render and after the underlying Qt Widgets are updated.

The setup function may return a cleanup function. If the dependencies in the next render are not __eq__ to the dependencies from the last render, then the cleanup function is called and then the new setup function is called.

The cleanup function will be called by Edifice exactly once for each call to the setup function. The cleanup function is called after render and before the component is deleted.

If the dependencies are None, then the new effect setup function will always be called after every render.

If you want to call the setup function only once, then pass an empty tuple () as the dependencies.

If the setup function raises an Exception then the cleanup function will not be called. Exceptions raised from the setup function and cleanup function will be suppressed.

The setup function can return None if there is no cleanup function.

The setup function and cleanup function can call the setter of a use_state() Hook to update the application state.

use_effect to attach and remove an event handler

@component
def Effective(self, handler):

    def setup_handler():
        token = attach_event_handler(handler)
        def cleanup_handler():
            remove_event_handler(token)
        return cleanup_handler

    use_effect(setup_handler, handler)

You can use use_effect to attach QWidget event handlers that are not supported by Edifice. For example, Edifice supports the resizeEvent with the on_resize prop for all Base Elements, but if it didn’t, then you could assign a custom on_resize_handler function this way.

use_effect to attach and remove a QWidget event handler

@component
def MyComponent(self):

    ref_textinput: Reference[TextInput] = use_ref()
    textinput_size, textinput_size_set = use_state((0, 0))

    def setup_resize_handler() -> Callable[[], None] | None:
        textinput = ref_textinput()

        if textinput is None or textinput.underlying is None:
            return

        def on_resize_handler(event: QtGui.QResizeEvent):
            textinput_size_set((event.size().width(), event.size().height()))

        # The resizeEvent method “can be reimplemented in a subclass to
        # receive widget resize events.” Or we can just assign to the
        # method because this is Python.
        textinput.underlying.resizeEvent = on_resize_handler

        def cleanup_resize_handler():
            # Restore the original resizeEvent method.
            textinput.underlying.resizeEvent = types.MethodType(
                type(textinput.underlying).resizeEvent, textinput.underlying
            )

        return cleanup_resize_handler

    use_effect(setup_resize_handler)

    with VBoxView():
        TextInput(text="Type here").register_ref(ref_textinput)
        Label(text=f"TextInput size: {ref_textinput().size()}")