Focus handling

This crate works by adding a FocusFlag to each widget's state.

Focus is used to collect the list of FocusFlags. It only holds references to the FocusFlags in the order the widgets are navigated. It is always constructed anew, this way any state dependent changes to the order/set of the widgets can be simply coded.

Focus::next()/Focus::prev() do the actual navigation. They change the active FocusFlag. Additionally, there are fields for focus-lost and focus-gained that are changed too.

The widget should implement HasFocusFlag for it's state, which makes coding easier.

Event-Handling

Event-handling is implemented for crossterm and uses only Tab/Backtab.

Focus implements HandleEvent for event-handling.

You can use also the function handle_focus() if you prefer.

These return Outcome::Changed whenever something focus related changes.

Mouse

Mouse support exists of course.

The trait HasFocusFlag has two methods to support this:

• area() - Returns the area of the widget that should react to mouse-clicks.

• z_areas() - Extends area(). Widgets can return more than one ZRect for mouse interaction, and each of those has an extra z-index to handle overlapping areas. Those can occur whenever the widget wants to render a popup/overlay on top of other widgets.

  This method is defaulted to return nothing which is good enough for most widgets.

  If z_areas is used, area must return the union of all Rects. Area is used as fast filter, z_areas are used for the details.

Macros

There are the macros on_lost, on_gained and match_focus that ease the use of the focus-flags, providing a match like syntax.

Composition

There is support for composite widgets too.

Use Focus::new_container() to create the list of widgets in a container. This takes one extra FocusFlag which creates a summary of the individual FocusFlags of each widget. This way the container widget has an answer to 'Does any of my widgets have the focus?'. The container can also have its own area. If the container area is clicked and not some specific widget, the first widget in the container gets the focus.

Lost/Gained also work for the whole container.

The trait HasFocus indicates the existence of this behaviour. Focus has a method add_container() for this too.

    There is a lighter version of a container too. 
    `Focus::new_grp()` creates a list of widgets, but without a container
    area.

Focus can handle recursive containers too.

HasFocusFlag

In addition to the before-mentioned methods there are

• navigable() - The widget can indicate that it is not reachable with key navigation.
• is_focused(), lost_focus(), gained_focus() - These are useful when writing the application.