Layouts

Detailed Description

A layout control derives the geometry of its children from a placement policy. It remains in the visual hierarchy: a form's content is often a layout, and a layout can nest other layouts. Attachment is non-owning. addItem() records the layout-specific placement and attaches the child; removeItem() detaches it. Control::add() attaches without that policy. Keep each child alive until it is detached.

Layouting follows the cycle in Layouting and Painting. Measure runs inside-out under a SizePolicy. Layout runs outside-in and assigns child geometry with move() and resize(). A layout implements those passes for its policy. Control::padding() is the inner inset of the layout. A child's Control::margin() is the outer gap around that child. Invisible children are skipped.

Choose a layout by the arrangement it produces.

FlowLayout Left              DockingLayout
+------------------+         +------------------+
| [A] [B] [C]      |         | Top              |
+------------------+         +----+--------+----+
                             |Left| Fill   |Right|
GridLayout Vertical, 3       +----+--------+----+
+---+---+---+                | Bottom           |
| A | B | C |                +------------------+
+---+---+---+
| D | E |   |
 
TableLayout2                 StackLayout
+--------+--------+          +------------------+
| 0,0    | 0,1    |          | current          |
+--------+--------+          | (others hidden)  |
| 1,0    | 1,1    |          +------------------+
+--------+--------+
 
CanvasLayout                 ScrollLayout
+------------------+         +------------------+
| A@(x,y)          |         | content > view   |
|        B@(x,y)   |         |            [====]|
+------------------+         +------------------+

A flow places children on one axis. Docking consumes edges in add order and gives leftover space to Fill. A grid uses uniform cells and wrapping. A table assigns children to row and column tracks that can prefer, fix, or fill size. A stack shows one child at a time. A canvas uses stored positions. A scroll layout offsets children when content exceeds the viewport; it is not a scroll view with bars.

Layout attributes refine placement without being layout controls. Spacing is the four-sided inset used as a control's margin or padding. Direction is the axis of a flow. Alignment places content in a rectangle. Adjustment aligns along one axis, typically a line of text.

Spacing                         Alignment
+------------------+            +---+---+---+
|      top         |            |TL | T |TR |
| left  [  ] right |            | L | C | R |
|     bottom       |            |BL | B |BR |
+------------------+            +---+---+---+
 
Direction                       Adjustment
Left -->   Top |                Left   |text    |
<-- Right      v                Center |  text  |
               Bottom           Right  |    text|

Classes
class	Adjustment
	Aligns content along one axis. More...
class	Alignment
	Names a position in a rectangle. More...
class	CanvasLayout
	Arranges children at stored positions and sizes. More...
class	Direction
	Names a flow direction. More...
class	DockingLayout
	Docks children to edges and fills leftover space. More...
class	FlowLayout
	Arranges children in a single row or column. More...
class	GridLayout
	Arranges children in uniform wrapping cells. More...
class	ScrollLayout
	Offsets children when content exceeds the viewport. More...
class	Spacing
	Stores four-sided inset values. More...
class	StackLayout
	Shows one child at a time. More...
class	TableLayout2
	Arranges children in row and column tracks. More...