paint method Null safety

  1. @override
void paint(
  1. PaintingContext context,
  2. Offset offset

Paint this render object into the given context at the given offset.

Subclasses should override this method to provide a visual appearance for themselves. The render object's local coordinate system is axis-aligned with the coordinate system of the context's canvas and the render object's local origin (i.e, x=0 and y=0) is placed at the given offset in the context's canvas.

Do not call this function directly. If you wish to paint yourself, call markNeedsPaint instead to schedule a call to this function. If you wish to paint one of your children, call PaintingContext.paintChild on the given context.

When painting one of your children (via a paint child function on the given context), the current canvas held by the context might change because draw operations before and after painting children might need to be recorded on separate compositing layers.


void paint(PaintingContext context, Offset offset) {
  if (!_hasOverflow) {
    defaultPaint(context, offset);

  // There's no point in drawing the children if we're empty.
  if (size.isEmpty)

  if (clipBehavior == Clip.none) {
    _clipRectLayer.layer = null;
    defaultPaint(context, offset);
  } else {
    // We have overflow and the clipBehavior isn't none. Clip it.
    _clipRectLayer.layer = context.pushClipRect(
      offset, & size,
      clipBehavior: clipBehavior,
      oldLayer: _clipRectLayer.layer,

  assert(() {
    // Only set this if it's null to save work. It gets reset to null if the
    // _direction changes.
    final List<DiagnosticsNode> debugOverflowHints = <DiagnosticsNode>[
        'The overflowing $runtimeType has an orientation of $_direction.',
        'The edge of the $runtimeType that is overflowing has been marked '
        'in the rendering with a yellow and black striped pattern. This is '
        'usually caused by the contents being too big for the $runtimeType.',
        'Consider applying a flex factor (e.g. using an Expanded widget) to '
        'force the children of the $runtimeType to fit within the available '
        'space instead of being sized to their natural size.',
        'This is considered an error condition because it indicates that there '
        'is content that cannot be seen. If the content is legitimately bigger '
        'than the available space, consider clipping it with a ClipRect widget '
        'before putting it in the flex, or using a scrollable container rather '
        'than a Flex, like a ListView.',

    // Simulate a child rect that overflows by the right amount. This child
    // rect is never used for drawing, just for determining the overflow
    // location and amount.
    final Rect overflowChildRect;
    switch (_direction) {
      case Axis.horizontal:
        overflowChildRect = Rect.fromLTWH(0.0, 0.0, size.width + _overflow, 0.0);
      case Axis.vertical:
        overflowChildRect = Rect.fromLTWH(0.0, 0.0, 0.0, size.height + _overflow);
    paintOverflowIndicator(context, offset, & size, overflowChildRect, overflowHints: debugOverflowHints);
    return true;