edifice.use_effect_final

class edifice.use_effect_final(cleanup, dependencies=())

Bases:

Side-effect Hook for when a edifice.component() unmounts.

This Hook will call the cleanup side-effect function with the latest local state from use_state() Hooks.

This Hook solves the problem of using use_effect() with constant deps to run a cleanup function when a component unmounts. If the use_effect() deps are constant so that the cleanup function only runs once, then the cleanup function will not have a closure on the latest component use_state state. This Hook cleanup function will always have a closure on the latest component use_state.

The optional dependencies argument can be used to trigger the Hook to call the cleanup function before the component unmounts.

Example:

x, set_x = ed.use_state(0)

def unmount_cleanup_x():
    print(f"At unmount, the value of x is {x}")

use_effect_final(unmount_cleanup_x)

Debounce

We can use this Hook together with use_async() to “debounce” an effect which must always finally run when the component unmounts.

Example:

x, set_x = ed.use_state(0)

# We want to save the value of x to a file whenever the value of
# x changes. But we don't want to do this too often because it would
# lag the GUI responses. Each :func:`use_async` call will cancel prior
# awaiting calls. So this will save 1 second after the last change to x.

async def save_x_debounce():
    await asyncio.sleep(1.0)
    save_to_file(x)

use_async(save_x_debouce, x)

# And we want to make sure that the final value of x is saved to
# the file when the component unmounts.

use_effect_final(lambda: save_to_file(x))