Rust Programming By Example

Model

We'll start with an empty model and we'll populate it later in this chapter:

pub struct Model {
}

As you can see, a model can be a simple structure. It could also be () if your widget don't need a model. Actually, it can be any type you want.

Besides the model, a widget needs to know the initial value of its model. To specify what it is, we need to implement the model() method of the Widget trait:

#[widget]
impl Widget for App {
    fn model() -> Model {
        Model {
        }
    }

    // …
}

Here, we use the #[widget] attribute provided by the relm_attributes crate. Attributes are currently an unstable feature of the language, that's why we use nightly. We'll see in the section about the declarative view why this attribute is needed. So, let's go back to ...