Crate floem

source ·
Expand description


Floem is cross-platform GUI framework for Rust 🦀. It aims to be extremely performant while providing world-class developer ergonomics.


Floem models the UI using a tree of View instances that is constructed once. Views are self-contained components that can be composed together to create complex UIs, capable of reacting to state changes and events.

To ensure good UI performance, view composition functions are not rerun in response to changes in the reactive system. Unnecessary rebuilds of views can be expensive. If you have a use case for which having a view composition function that responds to reactivity is essential, you may wish to consider dyn_container.

You can read more about authoring your own views or see all built-in views.


Widgets are specialized high-level views providing certain functionality. Common examples include buttons, labels or text input fields. For a list of Floem’s built-in widgets, refer here. You can try them out via the widget gallery example.

State management

Floem uses reactivity built on signals and effects for its state management. This design pattern has been popularized by SolidJS in the JavaScript ecosystem and directly inspired Leptos in the Rust ecosystem. Floem uses its own reactive system with an API that is nearly identical to the one in the leptos_reactive crate. To learn more about signals and effects, you may want to explore Leptos’ documentation and their book.

Local state

You can create a signal anywhere in the program using create_rw_signal or create_signal. When you use a signal’s value within a view by calling get or with, the runtime will automatically subscribe the correct side effects to changes in that signal, creating reactivity. To the programmer this is transparent. The reactivity “just works” by accessing the value where you want to use it.

fn app_view() -> impl View {
    let text = create_rw_signal("Hello world".to_string());
    v_stack((text_input(text), label(move || text.get()))).style(|s| s.padding(10.0))

In this example, text is a signal containing a String that can both be read from and written to. The signal is used in two different places in the vertical stack. The text input has direct access to the RwSignal and will mutate the underlying String when the user types in the input box. The reactivity will then trigger a rerender of the label with the updated text value.

create_signal returns a separated ReadSignal and WriteSignal for a variable. An existing RwSignal may be converted using RwSignal::read_only and RwSignal::write_only where necessary, but the reverse is not possible.

Global state

Global state can be implemented using provide_context and use_context.

Customizing appearance

You can style a View instance by calling its style method. You’ll need to import the floem::views::Decorators trait to use it. The style method takes a function exposing a Style parameter. Through this parameter, you can access methods that modify a variety of familiar properties like width, padding and background. Some Style properties such as font size are inherited from parent views and can be overridden.

Styles can be updated reactively using any signal. Here’s how to apply a gray background color while the value held by the active_tab signal equals 0:

label(|| "Some text").style(move |s| {
        .apply_if(active_tab.get() == 0, |s| s.background(Color::GRAY))

For additional information about styling, see here.

Themes and widget customizations

Floem widgets ship with default styling that can be customized to your liking using style classes. Take the text input widget for example: it exposes a style class TextInputClass. Any styling rules that are attached to this class using Style’s class method will be applied to the text input. Widgets may expose multiple classes to enable customization of different aspects of their UI. The labeled checkbox is an example of this: both the checkbox itself and the label next to it can be customized using CheckboxClass and LabeledCheckboxClass respectively.

To theme a window, call the style method on your root view and inject your stylesheet. In your WindowConfig, you may want to disable the injection of Floem’s default styling. The themes example is available as a reference.

Don’t have the time or patience to develop your own theme? Check the floem-themes GitHub topic for a list of reusable themes made by the community. This list is unmoderated.

Additional reading