size property
The size of this render box computed during layout.
This value is stale whenever this object is marked as needing layout. During performLayout, do not read the size of a child unless you pass true for parentUsesSize when calling the child's layout function.
The size of a box should be set only during the box's performLayout or performResize functions. If you wish to change the size of a box outside of those functions, call markNeedsLayout instead to schedule a layout of the box.
Implementation
Size get size {
assert(hasSize, 'RenderBox was not laid out: ${toString()}');
assert(() {
if (_size is _DebugSize) {
final _DebugSize _size = this._size;
assert(_size._owner == this);
if (RenderObject.debugActiveLayout != null) {
// We are always allowed to access our own size (for print debugging
// and asserts if nothing else). Other than us, the only object that's
// allowed to read our size is our parent, if they've said they will.
// If you hit this assert trying to access a child's size, pass
// "parentUsesSize: true" to that child's layout().
assert(debugDoingThisResize || debugDoingThisLayout ||
(RenderObject.debugActiveLayout == parent && _size._canBeUsedByParent));
}
assert(_size == this._size);
}
return true;
}());
return _size;
}@protected
Setting the size, in checked mode, triggers some analysis of the render box, as implemented by debugAssertDoesMeetConstraints, including calling the intrinsic sizing methods and checking that they meet certain invariants.
Implementation
@protected
set size(Size value) {
assert(!(debugDoingThisResize && debugDoingThisLayout));
assert(sizedByParent || !debugDoingThisResize);
assert(() {
if ((sizedByParent && debugDoingThisResize) ||
(!sizedByParent && debugDoingThisLayout))
return true;
assert(!debugDoingThisResize);
String contract, violation, hint;
if (debugDoingThisLayout) {
assert(sizedByParent);
violation = 'It appears that the size setter was called from performLayout().';
hint = '';
} else {
violation = 'The size setter was called from outside layout (neither performResize() nor performLayout() were being run for this object).';
if (owner != null && owner.debugDoingLayout)
hint = 'Only the object itself can set its size. It is a contract violation for other objects to set it.';
}
if (sizedByParent)
contract = 'Because this RenderBox has sizedByParent set to true, it must set its size in performResize().';
else
contract = 'Because this RenderBox has sizedByParent set to false, it must set its size in performLayout().';
throw FlutterError(
'RenderBox size setter called incorrectly.\n'
'$violation\n'
'$hint\n'
'$contract\n'
'The RenderBox in question is:\n'
' $this'
);
}());
assert(() {
value = debugAdoptSize(value);
return true;
}());
_size = value;
assert(() { debugAssertDoesMeetConstraints(); return true; }());
}