1 unstable release

0.3.0 Apr 11, 2024

#152 in Internationalization (i18n)


5.5K SLoC

{iced} Application Framework

Rizzen Yazston :iced-url: https://crates.io/crates/iced :iced_aw-url: https://crates.io/crates/iced_aw :i18n-url: https://crates.io/crates/i18n-rizzen-yazston :icu-url: https://crates.io/crates/icu :icu4x-url: https://icu4x.unicode.org/ :iced: pass:q[iced]

Welcome to the {iced} Application Framework project.

The goal is to provide a starting application framework for developing native multi-window {iced} applications.

This project uses the {iced-url}[{iced}] library crates (including {iced_aw-url}[iced_aw] community crate for additional widgets) for the GUI of the application.

In addition, the framework supports internationalisation as a feature option by using the crate {i18n-url}[i18n-rizzen-yazston] and various crates of the {icu4x-url}[ICU4X] project, the main crate being {icu-url}[icu].

To support various applications, all the application's feature capabilities are gated with build feature options (see Features section). Features that are not used can be simply deleted for the application, thus simplifying the source code by reducing the need for #[cfg(...)] and #[cfg(not()...)] statements.


The following features are available:

  • log: To enable logging for the application, and inserts a log level setting in Preferences window,

  • sync: To use sync::Arc instead of rc::Rc, their respective variants.

  • i18n: To enable international support. The design allows for all scripts, though currently only supports top to down scripts, due to icu currently only has flow direction information for top to bottom scripts (with plans to expand to all scripts). Uses the latest i18n version 0.9.1, that added new features.

  • persistent: Specifies whether session data will be saved on exit, and restored at application launch. This feature is required if wanting applications settings to be persistent across usage.

  • first_use: To enable the simplified Preferences window to appear first on first time use to allow user to set specific preferences settings, before opening the application's main window. This feature automatically enables the persistent feature.

  • clap: Enabled command line support, for applications that like to have the ability to pass options/command/etc to the application. Note version used is 4.4.3, as 4.5 requires rustc version 0.74.

In the Cargo.toml there is two default lines, one being commented out. One enables all the features, while the other enables none.

What is included

The application framework has the following capabilities:

  • If build with the first_use and i18n features for the application, the Preferences window will be displayed prompting the user to select the user interface language (currently using language tags while waiting for display name feature to be completed in ICU4X),

  • The following windows:

  • ConfirmExit: for demonstration purposes application is set to displayed when exiting (faking unsaved data),

  • Preferences: contains the user interface language setting, and optional log level setting,

  • FatalError: for displaying fatal error messages to users (helpful when not launched from console),

  • Information: a simple generic window to display a message to user,

  • Main: simply contains a menu bar,

  • About: simply demonstration of an about window.

  • Parent windows are generally disabled while popup window is displayed,

  • Traps the window decoration close button, to handle certain state cases,

  • Windows are resizable and movable, and if build with persistent feature their final position and size is saved on application termination and restored when application is relaunched.

  • Supports handling of error Results internally of the update() method and the 'Application::new()' method, using FatalError window to display uncaught errors.

  • Localisation of text and errors that supports internationalisation. Two demonstration languages included for almost all text. Deliberately the text displayed in Main window does not support localisation for demonstration purposes.

  • A trivial example for localisation on selected platforms. For MacOS target the menu bar and Confirm Exit windows uses "Quit <app_name>" instead of "Exit".


NOTE:: There are no build scripts included, and data files need to be copied to target destination.

As this project is a starting point for developing multi-windowed {iced} applications, it can be compiled into a functional example, and be launched by using the application name example.

Before launching the example copy the l10n directory to where the directory where the binary resides to avoid a panic indicating missing localisation database.

Edit the lib.rs in the project's root, to configure various application's consts to reflect the new project.

As this is a mini application framework for creating multi-window applications, feel free to remove unwanted features, easy to spot with #[cfg(...)] statements and deleted the associated statement/expression. Or alternative leave the features as is and continue using the feature #[cfg(...)] statements for new windows and new components of existing windows, to allow easy switching to more advance features later on (such as international support, or suddenly requiring command line options).


  • Menu items are always centred, current implementation of menu in iced_aw does not have methods or means to change alignment to start or end.

  • This still work in progress, thus the windows may look a bit wonky. Currently focused on functionality than appearances.

Adding a new windows

  • In src/window directory pick a window that closely fits your new window layout structure, copy rust file with a new filename.

  • Make the required changes in the new window .rs file:

  • Such as renaming ???Localisation struct, ??? struct, and display_??? function, where ??? is the window abbreviation name. Adjust the content of these as required.

  • If required add a ???Message enum, and update_??? function, where ??? is internal window abbreviation name. See existing preferences.rs for an example.

  • Alter the contents of try_new(), try_update() and view(), and optionally adjust parent_remove().

  • In window.rs add the new filename.

  • In core/session.rs add entry for the window in Ui struct.

  • In core/application:

  • To use crate::{ ... window::{ statement add the new window filename.

  • To WindowType add a new entry for the new window.

  • If new window has its own Message enum, add it to ApplicationMessage enum, to be able to pass messages to the new window's try_update() method.

  • To try_update() method, add match branch for new window, either directly to window's try_update() method, or if needing to do more logic outside of window's try_update() method, in the new window's rust file can add a update_? function, where ? is the window abbreviation. See other branches for examples.

  • To resized() and moved() methods add entries for the new window.

  • If new window is accessible from the application's menu bar then add entry in window/main/menu_bar.rs and add match branch to update_main() function to handle the displaying of the new window.

Design process

Almost all the methods of the i18n library uses the Result type to be able to provide runtime errors that are catchable, where the developer of the application (or another library) can decide to ignore the error, display the error, or leave it uncaught to become a fatal error (application terminating). This is an intentional design of the i18n project.

On the other hand the iced library does not support the Result type as the return type for the new(), update() and view() methods. The Result of various i18n methods needs to be caught and handled within the application's main new() and update() methods.

A new update method is created called try_update(), which contains all the logic that would have been in the application's update() method, and returns a Result type. This try_update() method is called within the update(), and if the result is the Ok() variant, then the Command enum is returned to the iced caller. However if the result is the Err() variant, then the FatalError state is created containing the error, and the resulting window spawn command is returned to the iced caller. The fatal error window, that is displayed, is a special type of window, in that it does not allow the Err() variant to be returned. Any error that occurs within the fatal error window's try_update() method is caught and handled, thus only the Ok() variant is returned containing a batch command to close all windows. The benefit of displaying the runtime fatal error before application closes, is when the application is not launched from a console where errors are normally displayed, and if logging is not supported to record the error in a logging system (usually files).

Similar approach is used for the new() method, where the actual logic is placed in a new method called try_new(). If the result is an error, the application terminates with a panic!(), that contains a simple formatted message of the error. Otherwise the contents of the Ok() variant is returned.

There is no equivalent try_view() method for view(), as no error must not occur. The view() method must only read the window state, and build the window accordingly. The window state at the time of creation must contain all the data required to be displayed, without requiring any form of formatting. The view() only allows the placing order to be altered, by reading fields of the window state. If the feature i18n is enabled, the localisation of text only takes place at the creation of the window state, or when updating the window state within the try_update() and try_update_localisation() methods of the window. However the application's main view() method does trap two possible errors when retrieving the window's actual view(), in this case the contents of the main window is replaced with an error message.

As see from above, there are references of the application's main try_update() and view() methods calling the window's actual try_update() and view(). This approach of separating the update and view logic into their own methods for each window, was due to that the match statements became unyielding large, making it difficult to follow the logic of the individual windows. To do this the WindowType and WindowTrait (along with the AnyWindowTrait to be able to downcast from Any) was introduced to provide an uniform way of calling windows actual try_update() and view() methods. This also allowed the main try_update and view() methods to be greatly simplified. Also using an enum for the WindowType, it allows the possibility of including a window number (usize) or identifier as a String to be used when the are multiple windows of the same type. In the window's try_update() and view() the value of the enum variant is used to make changes to the specific window of the WindowType variant.

The Message enum is also broken down into separate Message enums, one for each window if the application main Message enum and try_update() method does not contain the suitable message handling.


~844K SLoC