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User Input

Demonstrates one approach to accepting user input. Source user_input.rs.

:::caution Consider using tui-textarea or tui-input crates for more functional text entry UIs. :::

run
git clone https://github.com/ratatui/ratatui.git --branch latest
cd ratatui
cargo run --example=user_input --features=crossterm

user_input

user_input.rs
//! # [Ratatui] User Input example
//!
//! The latest version of this example is available in the [examples] folder in the repository.
//!
//! Please note that the examples are designed to be run against the `main` branch of the Github
//! repository. This means that you may not be able to compile with the latest release version on
//! crates.io, or the one that you have installed locally.
//!
//! See the [examples readme] for more information on finding examples that match the version of the
//! library you are using.
//!
//! [Ratatui]: https://github.com/ratatui/ratatui
//! [examples]: https://github.com/ratatui/ratatui/blob/main/examples
//! [examples readme]: https://github.com/ratatui/ratatui/blob/main/examples/README.md
// A simple example demonstrating how to handle user input. This is a bit out of the scope of
// the library as it does not provide any input handling out of the box. However, it may helps
// some to get started.
//
// This is a very simple example:
// * An input box always focused. Every character you type is registered here.
// * An entered character is inserted at the cursor position.
// * Pressing Backspace erases the left character before the cursor position
// * Pressing Enter pushes the current input in the history of previous messages. **Note: ** as
// this is a relatively simple example unicode characters are unsupported and their use will
// result in undefined behaviour.
//
// See also https://github.com/rhysd/tui-textarea and https://github.com/sayanarijit/tui-input/
use color_eyre::Result;
use ratatui::{
crossterm::event::{self, Event, KeyCode, KeyEventKind},
layout::{Constraint, Layout, Position},
style::{Color, Modifier, Style, Stylize},
text::{Line, Span, Text},
widgets::{Block, List, ListItem, Paragraph},
DefaultTerminal, Frame,
};
fn main() -> Result<()> {
color_eyre::install()?;
let terminal = ratatui::init();
let app_result = App::new().run(terminal);
ratatui::restore();
app_result
}
/// App holds the state of the application
struct App {
/// Current value of the input box
input: String,
/// Position of cursor in the editor area.
character_index: usize,
/// Current input mode
input_mode: InputMode,
/// History of recorded messages
messages: Vec<String>,
}
enum InputMode {
Normal,
Editing,
}
impl App {
const fn new() -> Self {
Self {
input: String::new(),
input_mode: InputMode::Normal,
messages: Vec::new(),
character_index: 0,
}
}
fn move_cursor_left(&mut self) {
let cursor_moved_left = self.character_index.saturating_sub(1);
self.character_index = self.clamp_cursor(cursor_moved_left);
}
fn move_cursor_right(&mut self) {
let cursor_moved_right = self.character_index.saturating_add(1);
self.character_index = self.clamp_cursor(cursor_moved_right);
}
fn enter_char(&mut self, new_char: char) {
let index = self.byte_index();
self.input.insert(index, new_char);
self.move_cursor_right();
}
/// Returns the byte index based on the character position.
///
/// Since each character in a string can be contain multiple bytes, it's necessary to calculate
/// the byte index based on the index of the character.
fn byte_index(&self) -> usize {
self.input
.char_indices()
.map(|(i, _)| i)
.nth(self.character_index)
.unwrap_or(self.input.len())
}
fn delete_char(&mut self) {
let is_not_cursor_leftmost = self.character_index != 0;
if is_not_cursor_leftmost {
// Method "remove" is not used on the saved text for deleting the selected char.
// Reason: Using remove on String works on bytes instead of the chars.
// Using remove would require special care because of char boundaries.
let current_index = self.character_index;
let from_left_to_current_index = current_index - 1;
// Getting all characters before the selected character.
let before_char_to_delete = self.input.chars().take(from_left_to_current_index);
// Getting all characters after selected character.
let after_char_to_delete = self.input.chars().skip(current_index);
// Put all characters together except the selected one.
// By leaving the selected one out, it is forgotten and therefore deleted.
self.input = before_char_to_delete.chain(after_char_to_delete).collect();
self.move_cursor_left();
}
}
fn clamp_cursor(&self, new_cursor_pos: usize) -> usize {
new_cursor_pos.clamp(0, self.input.chars().count())
}
fn reset_cursor(&mut self) {
self.character_index = 0;
}
fn submit_message(&mut self) {
self.messages.push(self.input.clone());
self.input.clear();
self.reset_cursor();
}
fn run(mut self, mut terminal: DefaultTerminal) -> Result<()> {
loop {
terminal.draw(|frame| self.draw(frame))?;
if let Event::Key(key) = event::read()? {
match self.input_mode {
InputMode::Normal => match key.code {
KeyCode::Char('e') => {
self.input_mode = InputMode::Editing;
}
KeyCode::Char('q') => {
return Ok(());
}
_ => {}
},
InputMode::Editing if key.kind == KeyEventKind::Press => match key.code {
KeyCode::Enter => self.submit_message(),
KeyCode::Char(to_insert) => self.enter_char(to_insert),
KeyCode::Backspace => self.delete_char(),
KeyCode::Left => self.move_cursor_left(),
KeyCode::Right => self.move_cursor_right(),
KeyCode::Esc => self.input_mode = InputMode::Normal,
_ => {}
},
InputMode::Editing => {}
}
}
}
}
fn draw(&self, frame: &mut Frame) {
let vertical = Layout::vertical([
Constraint::Length(1),
Constraint::Length(3),
Constraint::Min(1),
]);
let [help_area, input_area, messages_area] = vertical.areas(frame.area());
let (msg, style) = match self.input_mode {
InputMode::Normal => (
vec![
"Press ".into(),
"q".bold(),
" to exit, ".into(),
"e".bold(),
" to start editing.".bold(),
],
Style::default().add_modifier(Modifier::RAPID_BLINK),
),
InputMode::Editing => (
vec![
"Press ".into(),
"Esc".bold(),
" to stop editing, ".into(),
"Enter".bold(),
" to record the message".into(),
],
Style::default(),
),
};
let text = Text::from(Line::from(msg)).patch_style(style);
let help_message = Paragraph::new(text);
frame.render_widget(help_message, help_area);
let input = Paragraph::new(self.input.as_str())
.style(match self.input_mode {
InputMode::Normal => Style::default(),
InputMode::Editing => Style::default().fg(Color::Yellow),
})
.block(Block::bordered().title("Input"));
frame.render_widget(input, input_area);
match self.input_mode {
// Hide the cursor. `Frame` does this by default, so we don't need to do anything here
InputMode::Normal => {}
// Make the cursor visible and ask ratatui to put it at the specified coordinates after
// rendering
#[allow(clippy::cast_possible_truncation)]
InputMode::Editing => frame.set_cursor_position(Position::new(
// Draw the cursor at the current position in the input field.
// This position is can be controlled via the left and right arrow key
input_area.x + self.character_index as u16 + 1,
// Move one line down, from the border to the input line
input_area.y + 1,
)),
}
let messages: Vec<ListItem> = self
.messages
.iter()
.enumerate()
.map(|(i, m)| {
let content = Line::from(Span::raw(format!("{i}: {m}")));
ListItem::new(content)
})
.collect();
let messages = List::new(messages).block(Block::bordered().title("Messages"));
frame.render_widget(messages, messages_area);
}
}