belongs to Maven artifact com.android.support:gridlayout-v7:28.0.0-alpha1
GridLayout
public
class
GridLayout
extends ViewGroup
java.lang.Object | |||
↳ | android.view.View | ||
↳ | android.view.ViewGroup | ||
↳ | android.support.v7.widget.GridLayout |
A layout that places its children in a rectangular grid.
The grid is composed of a set of infinitely thin lines that separate the
viewing area into cells. Throughout the API, grid lines are referenced
by grid indices. A grid with N
columns
has N + 1
grid indices that run from 0
through N
inclusive. Regardless of how GridLayout is
configured, grid index 0
is fixed to the leading edge of the
container and grid index N
is fixed to its trailing edge
(after padding is taken into account).
Row and Column Specs
Children occupy one or more contiguous cells, as defined by theirrowSpec
and
columnSpec
layout parameters.
Each spec defines the set of rows or columns that are to be
occupied; and how children should be aligned within the resulting group of cells.
Although cells do not normally overlap in a GridLayout, GridLayout does
not prevent children being defined to occupy the same cell or group of cells.
In this case however, there is no guarantee that children will not themselves
overlap after the layout operation completes.
Default Cell Assignment
If a child does not specify the row and column indices of the cell it wishes to occupy, GridLayout assigns cell locations automatically using its:orientation
,
rowCount
and
columnCount
properties.
Space
Space between children may be specified either by using instances of the dedicatedSpace
view or by setting the
leftMargin
,
topMargin
,
rightMargin
and
bottomMargin
layout parameters. When the
useDefaultMargins
property is set, default margins around children are automatically
allocated based on the prevailing UI style guide for the platform.
Each of the margins so defined may be independently overridden by an assignment
to the appropriate layout parameter.
Default values will generally produce a reasonable spacing between components
but values may change between different releases of the platform.
Excess Space Distribution
GridLayout's distribution of excess space accommodates the principle of weight. In the event that no weights are specified, columns and rows are taken as flexible if their views specify some form of alignment within their groups.
The flexibility of a view is therefore influenced by its alignment which is,
in turn, typically defined by setting the
gravity
property of the child's layout parameters.
If either a weight or alignment were defined along a given axis then the component
is taken as flexible in that direction. If no weight or alignment was set,
the component is instead assumed to be inflexible.
Multiple components in the same row or column group are considered to act in parallel. Such a group is flexible only if all of the components within it are flexible. Row and column groups that sit either side of a common boundary are instead considered to act in series. The composite group made of these two elements is flexible if one of its elements is flexible.
To make a column stretch, make sure all of the components inside it define a weight or a gravity. To prevent a column from stretching, ensure that one of the components in the column does not define a weight or a gravity.
When the principle of flexibility does not provide complete disambiguation, GridLayout's algorithms favour rows and columns that are closer to its right and bottom edges. To be more precise, GridLayout treats each of its layout parameters as a constraint in the a set of variables that define the grid-lines along a given axis. During layout, GridLayout solves the constraints so as to return the unique solution to those constraints for which all variables are less-than-or-equal-to the corresponding value in any other valid solution.
Interpretation of GONE
For layout purposes, GridLayout treats views whose visibility status isGONE
, as having zero width and height. This is subtly different from
the policy of ignoring views that are marked as GONE outright. If, for example, a gone-marked
view was alone in a column, that column would itself collapse to zero width if and only if
no gravity was defined on the view. If gravity was defined, then the gone-marked
view has no effect on the layout and the container should be laid out as if the view
had never been added to it. GONE views are taken to have zero weight during excess space
distribution.
These statements apply equally to rows as well as columns, and to groups of rows or columns.
See GridLayout.LayoutParams
for a full description of the
layout parameters used by GridLayout.
Summary
Nested classes | |
---|---|
class |
GridLayout.Alignment
Alignments specify where a view should be placed within a cell group and what size it should be. |
class |
GridLayout.LayoutParams
Layout information associated with each of the children of a GridLayout. |
class |
GridLayout.Spec
A Spec defines the horizontal or vertical characteristics of a group of cells. |
Constants | |
---|---|
int |
ALIGN_BOUNDS
This constant is an |
int |
ALIGN_MARGINS
This constant is an |
int |
HORIZONTAL
The horizontal orientation. |
int |
|