Lens Map

The map() method on a lens can be used to derive data from the target of the lens. This is useful for when the lens target is not the right type for the binding, but a value of the correct type can be derived from it.

For example, let's say we have some string data representing a name in our model, but we only want to display the first letter within a label:

use vizia::prelude::*;

#[derive(Lens)]
pub struct AppData {
    pub name: String,
}

impl Model for AppData {}

fn main() -> Result<(), ApplicationError> {
    Application::new(|cx|{

        AppData {
            name: String::from("John Doe"),
        }.build(cx);

        Label::new(cx, AppData::name.map(|name| name.chars().nth(0).unwrap()));
    })
    .inner_size((400, 100))
    .run()
}

Note that in this example we're assuming that the string is not empty.

Now when the name field of the model changes the label will update to display the new first letter.