controlling_widgets_behavior.md

Controlling Widgets behavior

Some widgets cannot rely solely on state for some behavior changes. Take the TextInput, for example. Setting focus to a text input is not dependent on state. It's a one shot function call and the result is expected to simply work, assuming the text input exists.

The text input widget in Iced has a focus function for this exact scenario. It takes an text_input::Id as parameter, which is the id of the input. Before being able to set focus, we must set the id of the input by calling the id function.

Once everything is set, we can call focus passing the Id of the input.

Note on the below example that the update function in our MyApp returns a task. When this is the case, we must return a Task::none() after our match to satisfy the type constraint. Not all messages will return tasks, after all.

use iced::{
    Task,
    widget::{button, column, text_input},
};

fn main() -> iced::Result {
    iced::run("My App", MyApp::update, MyApp::view)
}

const MY_TEXT_ID: &str = "my_text";

#[derive(Debug, Clone)]
enum Message {
    EditText,
    UpdateText(String),
}

#[derive(Default)]
struct MyApp {
    some_text: String,
}

impl MyApp {
    fn update(&mut self, message: Message) -> Task<Message> {
        match message {
            Message::EditText => return text_input::focus(text_input::Id::new(MY_TEXT_ID)),
            Message::UpdateText(s) => self.some_text = s,
        }
        Task::none()
    }

    fn view(&self) -> iced::Element<Message> {
        column![
            button("Edit text").on_press(Message::EditText),
            text_input("", &self.some_text)
                .id(text_input::Id::new(MY_TEXT_ID))
                .on_input(Message::UpdateText),
        ]
        .into()
    }
}

➡️ Next: Dispatching Tasks at Startup

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