property size

The size of the RenderBox returned by findRenderObject.

This getter will only return a valid result after the layout phase is complete. It is therefore not valid to call this from the build function itself. It should only be called from paint callbacks or interaction event handlers (e.g. gesture callbacks).

For details on the different phases of a frame, see WidgetsBinding.beginFrame.

This getter will only return a valid result if findRenderObject actually returns a RenderBox. If findRenderObject returns a render object that is not a subtype of RenderBox (e.g., RenderView), this getter will throw an exception in checked mode and will return null in release mode.

Calling this getter is theoretically relatively expensive (O(N) in the depth of the tree), but in practice is usually cheap because the tree usually has many render objects and therefore the distance to the nearest render object is usually short.