If an item within a Column is not visible, or if it has a width or height of 0, the item will not be laid out and it will not be visible within the column. Also, since a Column automatically positions its children vertically, a child item within a Column should not set its y position or vertically anchor itself using the top, bottom, anchors.verticalCenter, fill or centerIn anchors. If you need to perform these actions, consider positioning the items without the use of a Column.

如果Column类中的组件不可视、width 或 height 为0，则此组件在此Column中不会显示。同时，Column会自动布局子组件的垂直坐标，因此子组件的有关y轴的锚点设置也不会生效。如果需要做verticalCenter、fill、centerIn 的anchors设定，不应该使用Column视图。