refactor: update List select behavior

* allow a selectable list to have no selected item
* show highlight_symbol only when something is selected

examples/demo.rs

@@ -355,7 +355,7 @@ fn draw_charts(f: &mut Frame<MouseBackend>, app: &App, area: Rect) {
             SelectableList::default()
                 .block(Block::default().borders(Borders::ALL).title("List"))
                 .items(&app.items)
-                .select(app.selected)
+                .select(Some(app.selected))
                 .highlight_style(Style::default().fg(Color::Yellow).modifier(Modifier::Bold))
                 .highlight_symbol(">")
                 .render(f, chunks[0]);

examples/list.rs

@@ -18,7 +18,7 @@ use tui::Terminal;
 struct App<'a> {
     size: Rect,
     items: Vec<&'a str>,
-    selected: usize,
+    selected: Option<usize>,
     events: Vec<(&'a str, &'a str)>,
     info_style: Style,
     warning_style: Style,
@@ -35,7 +35,7 @@ impl<'a> App<'a> {
                 "Item10", "Item11", "Item12", "Item13", "Item14", "Item15", "Item16", "Item17",
                 "Item18", "Item19", "Item20", "Item21", "Item22", "Item23", "Item24",
             ],
-            selected: 0,
+            selected: None,
             events: vec![
                 ("Event1", "INFO"),
                 ("Event2", "INFO"),
@@ -132,17 +132,31 @@ fn main() {
                 event::Key::Char('q') => {
                     break;
                 }
+                event::Key::Left => {
+                    app.selected = None;
+                }
                 event::Key::Down => {
-                    app.selected += 1;
-                    if app.selected > app.items.len() - 1 {
-                        app.selected = 0;
+                    app.selected = if let Some(selected) = app.selected {
+                        if selected >= app.items.len() - 1 {
+                            Some(0)
+                        } else {
+                            Some(selected + 1)
+                        }
+                    } else {
+                        Some(0)
+                    }
+                }
+                event::Key::Up => {
+                    app.selected = if let Some(selected) = app.selected {
+                        if selected > 0 {
+                            Some(selected - 1)
+                        } else {
+                            Some(app.items.len() - 1)
+                        }
+                    } else {
+                        Some(0)
                     }
                 }
-                event::Key::Up => if app.selected > 0 {
-                    app.selected -= 1;
-                } else {
-                    app.selected = app.items.len() - 1;
-                },
                 _ => {}
             },
             Event::Tick => {
@@ -153,6 +167,7 @@ fn main() {
     }
 
     terminal.show_cursor().unwrap();
+    terminal.clear().unwrap();
 }
 
 fn draw(t: &mut Terminal<MouseBackend>, app: &App) -> Result<(), io::Error> {
@@ -181,7 +196,7 @@ fn draw(t: &mut Terminal<MouseBackend>, app: &App) -> Result<(), io::Error> {
                         "WARNING" => &app.warning_style,
                         _ => &app.info_style,
                     },
-                    )
+                )
             });
             List::new(events)
                 .block(Block::default().borders(Borders::ALL).title("List"))

src/widgets/list.rs

@@ -137,7 +137,7 @@ where
 /// SelectableList::default()
 ///     .block(Block::default().title("SelectableList").borders(Borders::ALL))
 ///     .items(&["Item 1", "Item 2", "Item 3"])
-///     .select(1)
+///     .select(Some(1))
 ///     .style(Style::default().fg(Color::White))
 ///     .highlight_style(Style::default().modifier(Modifier::Italic))
 ///     .highlight_symbol(">>");
@@ -199,8 +199,8 @@ impl<'b> SelectableList<'b> {
         self
     }
 
-    pub fn select(mut self, index: usize) -> SelectableList<'b> {
-        self.selected = Some(index);
+    pub fn select(mut self, index: Option<usize>) -> SelectableList<'b> {
+        self.selected = index;
         self
     }
 }
@@ -216,16 +216,20 @@ impl<'b> Widget for SelectableList<'b> {
 
         // Use highlight_style only if something is selected
         let (selected, highlight_style) = match self.selected {
-            Some(i) => (i, &self.highlight_style),
-            None => (0, &self.style),
+            Some(i) => (Some(i), &self.highlight_style),
+            None => (None, &self.style),
         };
         let highlight_symbol = self.highlight_symbol.unwrap_or("");
         let blank_symbol = iter::repeat(" ")
             .take(highlight_symbol.width())
             .collect::<String>();
         // Make sure the list show the selected item
-        let offset = if selected >= list_height {
-            selected - list_height + 1
+        let offset = if let Some(selected) = selected {
+            if selected >= list_height {
+                selected - list_height + 1
+            } else {
+                0
+            }
         } else {
             0
         };
@@ -236,10 +240,14 @@ impl<'b> Widget for SelectableList<'b> {
             .iter()
             .enumerate()
             .map(|(i, item)| {
-                if i == selected {
-                    Item::StyledData(format!("{} {}", highlight_symbol, item), highlight_style)
+                if let Some(s) = selected {
+                    if i == s {
+                        Item::StyledData(format!("{} {}", highlight_symbol, item), highlight_style)
+                    } else {
+                        Item::StyledData(format!("{} {}", blank_symbol, item), &self.style)
+                    }
                 } else {
-                    Item::StyledData(format!("{} {}", blank_symbol, item), &self.style)
+                    Item::StyledData(format!("{}", item), &self.style)
                 }
             })
             .skip(offset as usize);