else if (alignment != null) {
current = Align(alignment: alignment!, child: current);
}
current 是 Container 逐层叠加的变量, 当alignment不为空时新包裹一层 Align 组件
else if (alignment != null) {
current = Align(alignment: alignment!, child: current);
}
current 是 Container 逐层叠加的变量, 当alignment不为空时新包裹一层 Align 组件