Tutorial Scheduler Single Execution Task

A single execution task is a closure or function that is executed only once, after a specified delay. As the delay can be 0, it can also be executed on the next frame. The scheduler method we will use is 'schedule_once'. The first parameter of this function is a &str which is the task name. You can use this name to cancel the task before it executes (see example at the bottom of this chapter). Here is an example of scheduling a single execution task with a closure, changing a label text after 3 seconds:

- Layout:
    - Label:
        id: my_label
        text: Waiting...

use std::time::Duration;
use ez_term::*;

let (root_widget, mut state_tree, mut scheduler) = load_ui();

let my_task = |context: Context| {

    let state = context.state_tree.get_mut("my_label").as_label_mut();
    state.set_text("3 seconds have passed!".to_string());
    state.update(context.scheduler);
};

scheduler.schedule_once("my_task", Box::new(my_task), Duration::from_secs(3));
run(root_widget, state_tree, scheduler);

The same example with a function:

use std::time::Duration;
use ez_term::*;
let (root_widget, mut state_tree, mut scheduler) = load_ui();

fn my_task(context: Context) {

    let state = context.state_tree.get_mut("my_label").as_label_mut();
    state.set_text("3 seconds have passed!".to_string());
    state.update(context.scheduler);
};

scheduler.schedule_once("my_task", Box::new(my_task), Duration::from_secs(3));
run(root_widget, state_tree, scheduler);

It is of course possible to schedule a task from a callback. For example, scheduling a task with delay after a button is pushed. Here is an example: we will bind a callback to a button, that will change the text of a label after 3 seconds, using a closure:

- Layout:
    mode: box
    orientation: vertical
    - Button:
        id: my_button
        text: Change text
        auto_scale: true, true
        halign: center
        padding_bottom: 2
    - Label:
        id: my_label
        text: Initial text
        auto_scale: true, true
        halign: center

use std::time::Duration;
use ez_term::*;
let (root_widget, mut state_tree, mut scheduler) = load_ui();


let my_callback = |context: Context| {

    let my_task = |context: Context| {

        let state = context.state_tree.get_mut("my_label").as_label_mut();
        state.set_text("Button was pressed 3 seconds ago!".to_string());
        state.update(context.scheduler);
    };

    let state = context.state_tree.get_mut("my_label").as_label_mut();
    state.set_text("Waiting...".to_string());
    state.update(context.scheduler);

    context.scheduler.schedule_once("my_task", Box::new(my_task), Duration::from_secs(3));
    true
};
let new_callback_config = CallbackConfig::from_on_press(Box::new(my_callback));
scheduler.update_callback_config("my_button", new_callback_config);

run(root_widget, state_tree, scheduler);

To cancel a run-once task use the 'cancel_task' method of the scheduler. Of course, this only works if it is called before the task is executed. If the task no longer exists this method will not panic, so it is always safe to try. Example:

scheduler.cancel_task("my_task");

Continue

The general tutorial continues with: Scheduled Recurring Exectution Tasks.