计算 widget 边界：

 static Rect getWidgetBoundary(GlobalKey key, {Offset offset = Offset.zero}) {
RenderBox widgetRenderBox = key.currentContext.findRenderObject();
Offset widgetOffset = widgetRenderBox.localToGlobal(Offset.zero);
Size size = widgetRenderBox.size;
final widgetCenter =
    Rect.fromLTWH(widgetOffset.dx, widgetOffset.dy, size.width, size.height).center;
return Rect.fromCenter(
    center: Offset(widgetCenter.dx + offset.dx, widgetCenter.dy + offset.dy),
    width: size.width,
    height: size.height);

}

计算文字大小：

static Size calculateTextSize(String text, TextStyle style,{double maxWidth,StrutStyle strutStyle}) {
final constraints = BoxConstraints(
  maxWidth:maxWidth?? double.infinity,
  minHeight: 0.0,
  minWidth: 0.0,
);
final renderParagraph = RenderParagraph(
    TextSpan(
      text: text,
      style: style,
    ),
    maxLines: 1,
    strutStyle:strutStyle??StrutStyle.fromTextStyle(style),
    textDirection: TextDirection.ltr)
  ..layout(constraints);

return Size(renderParagraph.getMinIntrinsicWidth(style.fontSize).ceilToDouble(),
    renderParagraph.getMinIntrinsicHeight(style.fontSize).ceilToDouble());
}

这个算出来的是一行的文字占多大宽度，具体计算成显示几行，需要 知道你限定一行展示多少，然后这算成显示成几行，然后乘以行间距

container 综合容器：

  class FlexibleContainer extends StatelessWidget {
  final double width;
  final double height;
  final EdgeInsetsGeometry margin;
  final EdgeInsetsGeometry padding;
  final Color borderColor;
  final double borderWidth;
  final BorderRadiusGeometry radius;
  final Color color;
  final DecorationImage image;
  final List<BoxShadow> shadows;
  final Alignment alignment;
  final bool needClip;
  final BoxShape shape;
  final Gradient gradient;
  final BoxConstraints constraints;

  final Widget child;

  FlexibleContainer(
      {Key key,
      this.width,
      this.height,
      this.constraints,
      this.margin,
      this.padding,
      this.borderColor,
      this.borderWidth = 1.0,
      this.shape = BoxShape.rectangle,
      this.color,
      this.radius = BorderRadius.zero,
      this.gradient,
      this.shadows,
      this.alignment,
      this.needClip = false,
      this.image,
      this.child})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
        height: height,
        width: width,
        margin: margin,
        padding: padding,
        constraints: constraints,
        alignment: alignment ?? Alignment.center,
        decoration: BoxDecoration(
            gradient: gradient,
            border: borderColor == null
                ? null
                : Border.all(
                    color: borderColor,
                    width: borderWidth,
                    style: BorderStyle.solid,
                  ),
            shape: shape,
            borderRadius: (shape == BoxShape.rectangle) ? (radius ?? BorderRadius.zero) : null,
            boxShadow: shadows,
            image: image,
            color: color),
        child: needClip
            ? (shape == BoxShape.circle
                ? ClipOval(
                    child: child,
                  )
                : ClipRRect(
                    borderRadius: radius,
                    child: child,
                  ))
            : child);
  }
}

使用overlay 实现自定义toast：

/**
*tips 要显示的文字
*key 需要设置显示的地方位于某个widget的下方的key，
**/
static Future showOverlayTips(BuildContext context, String tips, {Key key}) async {
    OverlayEntry overlayEntry;
    final screenSize = MediaQuery.of(context).size;
    double top = screenSize.height * 0.7;
    if (key != null) {
      final anchor = WidgetUtils.getWidgetBoundary(key);
      top = anchor.height;
    }

    final textStyle =
        TextStyle(color: Color(0xffffffff), fontSize: 11, fontWeight: FontWeight.w500);
    overlayEntry = OverlayEntry(builder: (BuildContext context) {
      return Positioned(
          top: top,
          child: Material(
            child: Container(
              width: screenSize.width,
              alignment: Alignment.center,
              child: Center(
                child: Card(
                  elevation: null,
                  borderOnForeground: false,
                  shadowColor: Colors.transparent,
                  shape: RoundedRectangleBorder(
                    borderRadius: BorderRadius.circular(4),
                  ),
                  color: Color(0x33000000),
                  child: Padding(
                    padding: EdgeInsets.symmetric(horizontal: 12, vertical: 5),
                    child: Text(
                      tips,
                      style: textStyle,
                    ),
                  ),
                ),
              ),
            ),
          ));
    });
    Overlay.of(context).insert(overlayEntry);
    Future.delayed(Duration(seconds: 2), () {
      overlayEntry.remove();
    });
  }

计算文字占用宽度

  static int calculateMaxLines(BuildContext context, String text, TextStyle style, double maxWidth,
      {TextAlign? textAlign, TextDirection? textDirection, StrutStyle? strutStyle}) {
    int lines = 1;
    late TextPainter textPainter;
    do {
      textPainter = TextPainter(
          textAlign: textAlign ?? TextAlign.left,
          textDirection: textDirection ?? TextDirection.ltr,
          locale: Localizations.localeOf(
            context,
          ),
          text: TextSpan(text: text, style: style),
          strutStyle: strutStyle,
          maxLines: lines);
      textPainter.layout(maxWidth: maxWidth);
      if ((textPainter.didExceedMaxLines || textPainter.width > maxWidth)) {
        lines++;
      }
    } while ((textPainter.didExceedMaxLines || textPainter.width > maxWidth));
    return lines;
  }