Positioned class

官方文档Positioned class

Positioned class

A widget that controls where a child of a Stack is positioned.

一个用来控制它的子控件在Stack中的放置位置。

A Positioned widget must be a descendant of a Stack, and the path from the Positioned widget to its enclosing Stack must contain only StatelessWidgets or StatefulWidgets (not other kinds of widgets, likeRenderObjectWidgets).

一个Positiond控件必须是Stack的子控件，在Positiond控件与装入它的Stack之间，必须只包含StatelessWidget或者StatefulWidget。（不能是别的类型，比如RenderObjectWidget）。

If a widget is wrapped in a Positioned, then it is a positioned widget in its Stack. If the top property is non-null, the top edge of this child will be positioned top layout units from the top of the stack widget. The right, bottom, and left properties work analogously.

如果一个控件被Positioned包裹，那么它在Stack中就是一个已经定位的控件。如果top属性不为空，则这个widget的顶部将与Stack的顶部间隔与top值相等单位的距离。右侧，底部和左侧属性的工作方式类似。

If both the top and bottom properties are non-null, then the child will be forced to have exactly the height required to satisfy both constraints. Similarly, setting the right and left properties to non-null values will force the child to have a particular width. Alternatively the width and height properties can be used to give the dimensions, with one corresponding position property (e.g. top and height).

如果top和bottom属性都不为空，则控件将被赋予满足这两项约束的高度。相同的，设置left和right属性，将为控件赋予满足约束的宽度。或者给出宽度或者高度属性，加上一个相应的位置属性，来声明控件尺寸（比如，top和height）。

If all three values on a particular axis are null, then the Stack.alignment property is used to position the child.

如果三个特定轴上的值都为空，则Stack.alignment属性将用来为子控件排序。

If all six values are null, the child is a non-positioned child. The Stack uses only the non-positioned children to size itself.

如果所有六个值都为空，则子控件是一个未定位的控件。Stack将会让未定位控件适应它的大小。

See also:

• PositionedDirectional, which adapts to the ambient Directionality.

• Inheritance

  Object> Diagnosticable> DiagnosticableTree> Widget> ProxyWidget> ParentDataWidget<Stack> >Positioned