Add support for partial view layouts
Traditionally, when a view called requestLayout it would force
recursive requestLayout calls for all parent views up the
hierarchy. This meant that there was no way to determine at traversal
time whether a parent view itself needed layout, or if just one of its
descendants did.
Add a ViewParent method requestPartialLayoutForChild(View). This lets
a caller state that a particular child of a given parent needs a
remeasure and relayout at its current measured size and position
within that parent. This can help prevent the full-tree relayout often
caused by otherwise trivial changes. Partial layouts are processed
after any pending "full" relayout during ViewRoot traversals, but
before drawing.
Add a ViewGroup method requestLayoutForChild(View). This lets a
ViewGroup decide whether it is more appropriate to request a
traditional relayout or a partial layout for itself or just the child
that changed.
Add a ViewParent method findDependentLayoutAxes. This allows a caller
to check if the ViewParent's layout is dependent on a specific direct
child view along one or both axes. Called recursively, this can be
used to determine if a change in a child view can be isolated to a
partial layout, even if its direct parent's own layout is tied to its
other ancestors. (e.g. MATCH_PARENT, LinearLayout weights)
Implement ViewGroup#requestPartialLayoutForChild to call new
ViewParent method findDependentLayoutAxes and based on the result,
either request a full layout for itself or a partial layout for the
child in question.
Implement findDependentLayoutAxes for common framework ViewGroups. A
private implementation in ViewGroup is available for use by framework
classes that will deal with basic LayoutParams. These implementations
specifically check for derived LayoutParams classes and abort the
optimization if they find something beyond their expected parameter
types.
Change-Id: I0a1a9b79293d17d4fae8d9892b96d3586f9401ae
13 files changed