Trait View

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pub trait View:
    Any
    + AnyView
    + Send
    + Sync {
    // Required method
    fn draw(&self, printer: &Printer<'_, '_>);

    // Provided methods
    fn layout(&mut self, _: XY<usize>) { ... }
    fn needs_relayout(&self) -> bool { ... }
    fn required_size(&mut self, constraint: XY<usize>) -> XY<usize> { ... }
    fn on_event(&mut self, _: Event) -> EventResult { ... }
    fn call_on_any(
        &mut self,
        _: &Selector<'_>,
        _: &mut dyn FnMut(&mut (dyn View + 'static)),
    ) { ... }
    fn focus_view(
        &mut self,
        _: &Selector<'_>,
    ) -> Result<EventResult, ViewNotFound> { ... }
    fn take_focus(
        &mut self,
        source: Direction,
    ) -> Result<EventResult, CannotFocus> { ... }
    fn important_area(&self, view_size: XY<usize>) -> Rect { ... }
    fn type_name(&self) -> &'static str { ... }
}

Expand description

Main trait defining a view behaviour.

This is what you should implement to define a custom View.

Required Methods§

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fn draw(&self, printer: &Printer<'_, '_>)

Draws the view with the given printer (includes bounds) and focus.

This is the only required method to implement.

Provided Methods§

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fn layout(&mut self, _: XY<usize>)

Called once the size for this view has been decided.

It can be used to pre-compute the configuration of child views.

View groups should propagate the information to their children.

At this point, the given size is final and cannot be negotiated. It is guaranteed to be the size available for the call to draw().

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fn needs_relayout(&self) -> bool

Should return true if the view content changed since the last call to layout().

This is mostly an optimisation for views where the layout phase is expensive.

Views can ignore it and always return true (default implementation). They will always be assumed to have changed.
View Groups can ignore it and always re-layout their children.
- If they call required_size or layout with stable parameters, the children may cache the result themselves and speed up the process anyway.

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fn required_size(&mut self, constraint: XY<usize>) -> XY<usize>

Returns the minimum size the view requires with the given restrictions.

This is the main way a view communicate its size to its parent.

Some views have a fixed size, and will ignore the constraint parameter entirely.

Some views are flexible, and may adapt fully or partially to the constraints.

Default implementation always return (1,1).

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fn on_event(&mut self, _: Event) -> EventResult

Called when an event is received (key press, mouse event, …).

You can return an EventResult:

EventResult::Ignored means the event was not processed and may be sent to another view.
EventResult::Consumed means the event was consumed and should not be sent to any other view. It may in addition include a callback to be run.

The default implementation just ignores any event.

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