flustars/lib/src/widget_util.dart

import 'package:flutter/widgets.dart';
import 'package:flutter/rendering.dart';

/**
 * @Author: thl
 * @GitHub: https://github.com/Sky24n
 * @Description: Widget Util.
 * @Date: 2018/9/10
 */

///
class WidgetUtil {
  bool _hasMeasured = false;
  double _width;
  double _height;

  /// Widget rendering listener.
  /// Widget渲染监听
  /// context: Widget context
  /// isOnce: true,Continuous monitoring  false,Listen only once.
  /// onCallBack: Widget Rect CallBack
  void asyncPrepare(
      BuildContext context, bool isOnce, ValueChanged<Rect> onCallBack) {
    if (_hasMeasured) return;
    WidgetsBinding.instance.addPostFrameCallback((Duration timeStamp) {
      RenderBox box = context.findRenderObject();
      if (box != null && box.semanticBounds != null) {
        if (isOnce) _hasMeasured = true;
        double width = box.semanticBounds.width;
        double height = box.semanticBounds.height;
        if (_width != width || _height != height) {
          _width = width;
          _height = height;
          if (onCallBack != null) onCallBack(box.semanticBounds);
        }
      }
    });
  }

  ///get Widget Bounds (width, height, left, top, right, bottom and so on).Widgets must be rendered completely.
  ///获取widget Rect
  static Rect getWidgetBounds(BuildContext context) {
    RenderBox box = context.findRenderObject();
    return (box != null && box.semanticBounds != null)
        ? box.semanticBounds
        : Rect.zero;
  }

  ///Get the coordinates of the widget on the screen.Widgets must be rendered completely.
  ///获取widget在屏幕上的坐标,widget必须渲染完成
  static Offset getWidgetLocalToGlobal(BuildContext context) {
    RenderBox box = context.findRenderObject();
    return box == null ? Offset.zero : box.localToGlobal(Offset.zero);
  }
}