flutter 总结: 通过 GlobalKey 获取界面任意元

最初：

需求开发中遇到要获取屏幕任意元素坐标尺寸的功能，最终实现如下：

1. example：

//...
GlobalKey _globalKey = GlobalKey();

@override
Widget build(BuildContext context) {
    //...
    ElevatedButton.icon(
      icon: Icon(Icons.send),
      label: Text("发送"),
      // onPressed: () => ddlog('pressed'),
      key: _globalKey,
      onPressed: (){
        // _showCustomPopView();
        ddlog(_globalKey.position());// Offset(143.5, 117.0)
        ddlog(_globalKey.size);// Size(88.0, 48.0)
      },
    ),
    //...
}

2. extension 封装：

import 'package:flutter/material.dart';

extension BuildContextExt on BuildContext {

  /// 获取当前组件的 RenderBox
  RenderBox? renderBox() {
    return this.findRenderObject() is RenderBox ? (this.findRenderObject() as RenderBox) : null;
  }

  /// 获取当前组件的 position
  Offset? position({Offset offset = Offset.zero}) {
    return this.renderBox()?.localToGlobal(offset);
  }
}


extension GlobalKeyExt on GlobalKey{

  /// 获取当前组件的 RenderBox
  RenderBox? renderBox() => this.currentContext?.renderBox();

  /// 获取当前组件的 position
  Offset? position({Offset offset = Offset.zero}) => this.currentContext?.position(offset: offset);

  /// 获取当前组件的 Size
  Size? get size  => this.currentContext?.size;

}