computeDistanceToActualBaseline method
- @protected
Returns the distance from the y-coordinate of the position of the box to the y-coordinate of the first given baseline in the box's contents, if any, or null otherwise.
Do not call this function directly. If you need to know the baseline of a child from an invocation of performLayout or paint, call getDistanceToBaseline.
Subclasses should override this method to supply the distances to their baselines. When implementing this method, there are generally three strategies:
-
For classes that use the ContainerRenderObjectMixin child model, consider mixing in the RenderBoxContainerDefaultsMixin class and using RenderBoxContainerDefaultsMixin.defaultComputeDistanceToFirstActualBaseline.
-
For classes that define a particular baseline themselves, return that value directly.
-
For classes that have a child to which they wish to defer the computation, call getDistanceToActualBaseline on the child (not computeDistanceToActualBaseline, the internal implementation, and not getDistanceToBaseline, the public entry point for this API).
Implementation
@protected
double computeDistanceToActualBaseline(TextBaseline baseline) {
assert(_debugDoingBaseline, 'Please see the documentation for computeDistanceToActualBaseline for the required calling conventions of this method.');
return null;
}