Flutter Tricks: Widget Size & Position

[popeyelau]

import 'package:flutter/material.dart';

class ContextUtils {
  // Takes a key, and in 1 frame, returns the size of the context attached to the key
  static void getFutureSizeFromGlobalKey(GlobalKey key, Function(Size size) callback) {
    Future.microtask(() {
      Size size = getSizeFromContext(key.currentContext);
      if (size != null) {
        callback(size);
      }
    });
  }

  // Shortcut to get the renderBox size from a context
  static Size getSizeFromContext(BuildContext context) {
    RenderBox rb = context.findRenderObject() as RenderBox;
    return rb?.size ?? Size.zero;
  }

  // Shortcut to get the global position of a context
  static Offset getOffsetFromContext(BuildContext context, [Offset offset = null]) {
    RenderBox rb = context.findRenderObject() as RenderBox;
    return rb?.localToGlobal(offset ?? Offset.zero);
  }
}

Flutter Tricks: Widget Size & Position

[popeyelau]

• Flutter: How to measure Widgets

class MeasureSizeRenderObject extends RenderProxyBox {
  MeasureSizeRenderObject(this.onChange);
  void Function(Size size) onChange;

  Size _prevSize;
  @override
  void performLayout() {
    super.performLayout();
    Size newSize = child.size;
    if (_prevSize == newSize) return;
    _prevSize = newSize;
    WidgetsBinding.instance.addPostFrameCallback((_) => onChange(newSize));
  }
}

class MeasurableWidget extends SingleChildRenderObjectWidget {
  const MeasurableWidget({Key key, @required this.onChange, @required Widget child}) : super(key: key, child: child);
  final void Function(Size size) onChange;
  @override
  RenderObject createRenderObject(BuildContext context) => MeasureSizeRenderObject(onChange);
}