Learn Rust Coding · Lesson

Managing App State

Hold and update UI data.

State on the App Struct

In egui your application state is plain Rust data living on the struct that implements eframe::App. There is no special store or framework-owned model.

Fields hold everything: form inputs, selections, loaded data, flags. Each frame, update reads and mutates these fields directly through &mut self.

struct App {
    query: String,
    results: Vec<Item>,
    selected: Option<usize>,
    loading: bool,
}

Deriving Default

eframe builds your app in a closure passed to run_native. The simplest pattern is #[derive(Default)] and constructing with App::default().

For non-default initial values, implement Default by hand or add a constructor that takes the CreationContext for setup like fonts or persistence.

impl App {
    fn new(cc: &eframe::CreationContext) -> Self {
        let mut app = Self::default();
        app.dark = cc.egui_ctx.style().visuals.dark_mode;
        app
    }
}

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