headers property
The headers that will be laid out above each corresponding child in
children.
All headers but the first will be passed into SplitPane.splitters when
creating the SplitPane widget in build. Instead of being passed into
SplitPane.splitters, it will be combined with the first child in children
to create the first child we will pass into SplitPane.children.
We do this because the first header will not actually be a splitter as there is not any content above it for it to split.
We modify other values _children, _initialFractions, and _minSizes
from children, initialFractions, and minSizes, respectively, to
account for the first header. We do this adjustment here so that the
creators of FlexSplitColumn can be unaware of the under-the-hood
calculations necessary to achieve the UI requirements specified by
initialFractions and minSizes.
Implementation
final List<PreferredSizeWidget> headers;