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322 lines
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<ol class="chapter"><li><a href="feature_flags.html"><strong aria-hidden="true">1.</strong> Feature Flags</a></li><li><a href="command.html"><strong aria-hidden="true">2.</strong> Command API</a></li><li><a href="styling.html"><strong aria-hidden="true">3.</strong> Styling Output</a></li><li><a href="input.html" class="active"><strong aria-hidden="true">4.</strong> Reading Input Events</a></li><li><a href="screen.html"><strong aria-hidden="true">5.</strong> Alternate, Raw Screen</a></li></ol>
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<main>
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<blockquote>
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<p><strong>WARNING</strong>: This book is deprecated, no longer maintained and will be
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removed soon.</p>
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</blockquote>
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<p>Crossterm provides a way to work with the terminal input. We will not cover the basic usage but instead asynchronous and synchronous reading of input.
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Please check out these <a href="https://github.com/crossterm-rs/crossterm/blob/master/examples/input.rs">examples</a> for reading a line or a character from the user.</p>
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<a class="header" href="#differences-synchronous-and-asynchronous" id="differences-synchronous-and-asynchronous"><h2>Differences Synchronous and Asynchronous</h2></a>
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<p>Crossterm provides two ways to read user input, synchronous and asynchronous.</p>
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<a class="header" href="#synchronous-reading" id="synchronous-reading"><h3>Synchronous reading</h3></a>
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<p>Read the input synchronously from the user, the reads performed will be blocking calls.
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Using synchronous over asynchronous reading has the benefit that it is using fewer resources than the asynchronous because background thread and queues are left away.</p>
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<p>You can get asynchronous event reader by calling: <code>TerminalInput::read_sync</code>.</p>
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<a class="header" href="#asynchronous-reading" id="asynchronous-reading"><h3>Asynchronous reading</h3></a>
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<p>Read the input asynchronously, input events are gathered in the background and will be queued for you to read.
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Using asynchronous reading has the benefit that input events are queued until you read them. You can poll for occurred events, and the reads won't block your program.</p>
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<p>You can get a synchronous event reader by calling: <code>TerminalInput::read_async</code>, <code>TerminalInput::read_async_until</code>.</p>
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<a class="header" href="#technical-details" id="technical-details"><h3>Technical details</h3></a>
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<p>On UNIX systems crossterm reads from the TTY, on Windows, it uses <code>ReadConsoleInputW</code>.
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For asynchronous reading, a background thread will be fired up to read input events,
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occurred events will be queued on an MPSC-channel, and the user can iterate over those events.</p>
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<p>The terminal has to be in raw mode, raw mode prevents the input of the user to be displayed on the terminal screen, see <a href="screen.html">screen</a> for more info.</p>
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<a class="header" href="#example" id="example"><h1>Example</h1></a>
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<p>In the following example, we will create a small program that will listen for mouse and keyboard input.
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On the press of the 'escape' key, the program will be stopped.</p>
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<p>So let's start by setting up the basics.</p>
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<pre><code>use std::{thread, time::Duration};
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use crossterm::{input, InputEvent, KeyEvent};
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fn main() {
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println!("Press 'ESC' to quit.");
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/* next code here */
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}
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</code></pre>
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<p>Next, we need to put the terminal into raw mode. We do this because we don't want the user input to be printed to the terminal screen.</p>
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<pre><pre class="playpen"><code class="language-rust">
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# #![allow(unused_variables)]
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#fn main() {
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// enable raw mode
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let screen = RawScreen::into_raw_mode();
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// create a input from our screen
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let input = input();
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/* next code here */
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#}</code></pre></pre>
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<p>Now that we constructed a <code>TerminalInput</code> instance we can go ahead an start the reading.
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Do this by calling <code>input.read_async()</code>, which returns an <a href="https://docs.rs/crossterm/0.8.0/crossterm/struct.AsyncReader.html">AsyncReader</a>.
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This is an iterator over the input events that you could as any other iterator.</p>
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<pre><pre class="playpen"><code class="language-rust">
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# #![allow(unused_variables)]
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#fn main() {
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let mut async_stdin = input.read_async();
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loop {
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if let Some(key_event) = async_stdin.next() {
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/* next code here */
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}
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thread::sleep(Duration::from_millis(50));
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}
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#}</code></pre></pre>
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<p>The <a href="https://docs.rs/crossterm/0.8.0/crossterm/struct.AsyncReader.html">AsyncReader</a> iterator will return <code>None</code> when nothing is there to read, <code>Some(InputEvent)</code> if there are events to read.
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I use a thread delay to prevent spamming the iterator.</p>
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<p>Next up we can start pattern matching to see if there are input events we'd like to catch.
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In our case, we want to catch the <code>Escape Key</code>.</p>
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<pre><pre class="playpen"><code class="language-rust">
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# #![allow(unused_variables)]
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#fn main() {
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match key_event {
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InputEvent::Keyboard(event) => match event {
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KeyEvent::Esc => {
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println!("Program closing ...");
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break
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}
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_ => println!("Key {:?} was pressed!", event)
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}
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InputEvent::Mouse(event) => { /* Mouse Event */ }
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_ => { }
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}
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#}</code></pre></pre>
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<p>As you see, we check if the <code>KeyEvent::Esc</code> was pressed, if that's true we stop the program by breaking out of the loop.</p>
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<p><em>final code</em></p>
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<pre><pre class="playpen"><code class="language-rust">use std::{thread, time::Duration};
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use crossterm::{input, InputEvent, KeyEvent, RawScreen};
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fn main() {
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println!("Press 'ESC' to quit.");
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// enable raw mode
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let screen = RawScreen::into_raw_mode();
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// create a input from our screen.
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let input = input();
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// create async reader
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let mut async_stdin = input.read_async();
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loop {
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// try to get the next input event.
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if let Some(key_event) = async_stdin.next() {
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match key_event {
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InputEvent::Keyboard(event) => match event {
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KeyEvent::Esc => {
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println!("Program closing ...");
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break
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}
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_ => println!("Key {:?} was pressed!", event)
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}
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InputEvent::Mouse(event) => { /* Mouse Event */ }
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_ => { }
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}
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}
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thread::sleep(Duration::from_millis(50));
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}
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} // <=== background reader will be disposed when dropped.s
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</code></pre></pre>
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<hr />
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<p>More robust and complete examples on all input aspects like mouse, keys could be found <a href="https://github.com/crossterm-rs/crossterm/tree/master/examples/">here</a>.</p>
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