Agora Flutter SDK：一套代码，实现双端通话（二）

flutter: constraints: BoxConstraints(100.0<=w<=375.0, 100.0<=h<=300.0)flutter: childParentData: offset=Offset(275.0, 200.0)flutter: size: Size(375.0, 300.0)

Stingy(    child: RaisedButton(      child: Text('Button'),    onPressed: (){}  )  )

/// The [delegate] argument must not be null.
CustomMultiChildLayout({  Key key,  @required this.delegate,  List<Widget> children = const <Widget>[],})

  /// The delegate that controls the layout of the children.  final MultiChildLayoutDelegate delegate;

/// Each child must be wrapped in a [LayoutId] widget to identify the widget for  /// the delegate.

  /// Marks a child with a layout identifier.  /// Both the child and the id arguments must not be null.  LayoutId({    Key key,    @required this.id,        @required Widget child  })

Container(   child: CustomMultiChildLayout(     delegate: _LabelDelegate(itemCount: items.length, childId: childId),     children: items,   ), )

class _LabelDelegate extends MultiChildLayoutDelegate {  final int itemCount;  final String childId;    // x 方向上的偏移量  double dx = 0.0;    // y 方向上的偏移量  double dy = 0.0;
  _LabelDelegate({@required this.itemCount, @required this.childId});    @override  void performLayout(Size size) {    // 获取父控件的 width    double parentWidth = size.width;            for (int i = 0; i < itemCount; i++) {            // 获取子控件的 id      String id = '${this.childId}$i';         // 验证该 childId 是否对应一个 非空的 child      if (hasChild(id)) {              // layout child 并获取该 child 的 size        Size childSize = layoutChild(id, BoxConstraints.loose(size));        // 换行条件判断        if (parentWidth - dx < childSize.width) {          dx = 0;          dy += childSize.height;        }                // 根据 Offset 来放置 child        positionChild(id, Offset(dx, dy));        dx += childSize.width;      }    }  }      /// 该方法用来判断重新 layout 的条件  @override  bool shouldRelayout(_LabelDelegate oldDelegate) {      return oldDelegate.itemCount != this.itemCount;  }}

  /// Override this method to lay out and position all children given this  /// widget's size.  ///  /// This method must call [layoutChild] for each child. It should also specify  /// the final position of each child with [positionChild].  void performLayout(Size size);