Added background-tasks example

examples/background-tasks.rs

@@ -0,0 +1,56 @@
+//! This example shows how dynamic values make it easy to communicate state back
+//! to widgets from multiple threads.
+
+use std::time::Duration;
+
+use gooey::animation::ZeroToOne;
+use gooey::value::{Dynamic, Switchable};
+use gooey::widget::MakeWidget;
+use gooey::widgets::progress::{Progress, Progressable};
+use gooey::Run;
+
+#[derive(Debug, Default, Eq, PartialEq)]
+struct Task {
+    progress: Dynamic<Progress>,
+}
+
+fn main() -> gooey::Result {
+    let task = Dynamic::new(None::<Task>);
+
+    task.switcher(|task, dynamic| {
+        if let Some(task) = task {
+            // A background thread is running, show a progress bar.
+            task.progress.clone().progress_bar().make_widget()
+        } else {
+            // There is no background task. Show a button that will start one.
+            "Start"
+                .into_button()
+                .on_click({
+                    let task = dynamic.clone();
+                    move |()| {
+                        let background_task = Task::default();
+                        spawn_background_thread(&background_task.progress, &task);
+                        task.set(Some(background_task));
+                    }
+                })
+                .make_widget()
+        }
+    })
+    .contain()
+    .centered()
+    .run()
+}
+
+fn spawn_background_thread(progress: &Dynamic<Progress>, task: &Dynamic<Option<Task>>) {
+    let progress = progress.clone();
+    let task = task.clone();
+    std::thread::spawn(move || background_task(&progress, &task));
+}
+
+fn background_task(progress: &Dynamic<Progress>, task: &Dynamic<Option<Task>>) {
+    for i in 0_u8..=10 {
+        progress.set(Progress::Percent(ZeroToOne::new(f32::from(i) / 10.)));
+        std::thread::sleep(Duration::from_millis(100));
+    }
+    task.set(None);
+}

src/widgets/progress.rs

@@ -52,9 +52,10 @@ impl ProgressBar {
 }
 
 /// A measurement of progress for an indicator widget like [`ProgressBar`].
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Default)]
 pub enum Progress<T = ZeroToOne> {
     /// The task has an indeterminant length.
+    #[default]
     Indeterminant,
     /// The task is a specified amount complete.
     Percent(T),