invokeLayoutCallback<T extends Constraints> method

  1. @protected
void invokeLayoutCallback <T extends Constraints>(LayoutCallback<T> callback)
@protected

Allows mutations to be made to this object's child list (and any descendants) as well as to any other dirty nodes in the render tree owned by the same PipelineOwner as this object. The callback argument is invoked synchronously, and the mutations are allowed only during that callback's execution.

This exists to allow child lists to be built on-demand during layout (e.g. based on the object's size), and to enable nodes to be moved around the tree as this happens (e.g. to handle GlobalKey reparenting), while still ensuring that any particular node is only laid out once per frame.

Calling this function disables a number of assertions that are intended to catch likely bugs. As such, using this function is generally discouraged.

This function can only be called during layout.

Implementation 

@protected
void invokeLayoutCallback<T extends Constraints>(LayoutCallback<T> callback) {
  assert(_debugMutationsLocked);
  assert(_debugDoingThisLayout);
  assert(!_doingThisLayoutWithCallback);
  _doingThisLayoutWithCallback = true;
  try {
    owner._enableMutationsToDirtySubtrees(() { callback(constraints); });
  } finally {
    _doingThisLayoutWithCallback = false;
  }
}