[][src]Module cursive::view

Base elements required to build views.

Views are the main building blocks of your UI.

A view can delegate part or all of its responsabilities to child views, forming a view tree. The root of this tree is a StackView handled directly by the Cursive element.


The layout phase is when the size and location of each view is computed.

Each view is given an area of the screen by the View::layout() method. With this, the view is free to plan its content, including calling View::layout() on its own children.

In order to determine how much space should be given each child, parents can use View::required_size() on them.


When building new Views, you should respect these contracts:

  • By default, View::layout() should be called before any call to View::draw() with the same available size. The only exceptions is when both following conditions are met:

    • The available size has not changed since the last call to View::layout()
    • View::needs_relayout() returns false

    In this case, it is safe to omit the call to View::layout().

  • The value returned by required_size should be an actually viable size, no matter what the request is. This means calling View::layout() with a size returned by required_size is never an error.


In most layouts, a single view is active at any given time. This focus may change in response to events (for example presing the Tab key often moves to the next item).

This focus system involves two mechanics:

  • Individual views can decide whether they can be focused or not, through the View::take_focus() method. For example, unless disabled, a Button would accept focus (and return true from take_focus()), but a simple TextView or a divider would not (they would return false).
  • View groups like LinearLayout listen to events ignored by their children, and change their focus accordingly. For example, if the Tab key is pressed but the currently focused child of the LinearLayout ignores this event, then the LinearLayout will attempt to focus the next child. If no child accept the focus, then it will ignore the event as well.


Most views do not scroll by themselves; instead, they should be wrapped in a ScrollView to enable scrolling. The ScrollView will pretend that the wrapped view has been given a large enough area to fit entirely, but in reality only a part of that will be visible.

The wrapped view can ignore this and just draw itself as usual: the Printer will transparently translate the calls, and print commands outside of the visible area will simply be ignored.

In some cases however it may be interesting for the nested view to know about this, maybe to avoid computing parts of the view that are not visible. Printer::output_size and Printer::content_offset can be used to find out what part of the view should actually be printed.

Important Area

Sometimes, the wrapped view needs to communicate back to the ScrollView what part of the view is really important and should be kept visible.

For example, imagine a vertical list of buttons. When the user selects the next button, we want to scroll down a bit so the button becomes visible if it wasn't. To achieve this, the vertical LinearLayout communicates its "important area" (the currently active button) to the parent ScrollView, and the ScrollView makes sure that this area stays in view.



Core mechanisms to implement scrolling.



Four values representing each direction.


Provide scrolling functionalities to a view.


Cache around a one-dimensional layout result.


Represents a path to a single view in the layout.



Single-dimensional offset policy.


Defines the scrolling behaviour on content or size change


Selects a single view (if any) in the tree.


Single-dimensional constraint on a view size.



A view that can be downcasted to its concrete type.


Makes a view wrappable in a ResizedView.


Provides call_on<V: View> to views.


Makes a view wrappable in an NamedView.


Represents a type that can be made into a Box<View>.


Makes a view wrappable in an NamedView.


Makes a view wrappable in a ResizedView.


Makes a view wrappable in a ScrollView.


Main trait defining a view behaviour.


Generic wrapper around a view.

Type Definitions


Location of the view on screen