引入库：flutter_screenutil、image_gallery_saver、qr_flutter弹窗布局

import 'dart:async';
import 'dart:typed_data';
import 'package/generated/l10n.dart';
import 'package:jade/configs/PathConfig.dart';
import 'package:jade/utils/ImageWaterMarkUtil.dart';
import 'package:jade/utils/JadeColors.dart';
import 'package:jade/utils/Utils.dart';
import 'package:util/easy_loading_util.dart';
import 'package:util/navigator_util.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter_screenutil/flutter_screenutil.dart';
import 'package:image_gallery_saver/image_gallery_saver.dart';
import 'package:qr_flutter/qr_flutter.dart';import 'dart:ui' as ui;
/*
* 普通说明弹窗（可隐藏取消按钮）
* */
Widget productQrcodeDialog (
    BuildContext context,
    { String descTitle,
      String subTitle,
      String desc,
      String qrStr,
      GlobalKey globalKey,
      Function callback,
      Function cancelCallback,
      bool showCancel = false,
      String sureBtnText,
      Color sureBtnTextColor
    }){
  return UnconstrainedBox(
      child: Container(
        alignment: Alignment.center,
        width: Utils().screenWidth(context)*0.8,
        decoration: BoxDecoration(
          color: Colors.white,
          borderRadius: BorderRadius.circular(20),
        ),
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            if(descTitle != null)
              Container(
                  margin: EdgeInsets.only(top: 50.w),
                  child: Text(descTitle??'',style: TextStyle(color: JadeColors.grey_2,fontSize: 38.sp,fontWeight: FontWeight.w600))
              ),
            if(subTitle != null)
              Container(
                  margin: EdgeInsets.only(top: 20.w),
                  child: Text(subTitle,style: TextStyle(color: JadeColors.grey,fontSize: 24.sp))
              ),
            if(desc != null)
              Container(
                  margin: EdgeInsets.only(top: 30.w,bottom: 30.w),
                  padding: EdgeInsets.symmetric(horizontal: 30.w),
                  child: Text(desc,style: TextStyle(color: JadeColors.grey_2,fontSize: 30.sp),maxLines: 300,textAlign: TextAlign.center,)
              ),
            RepaintBoundary(
                key: globalKey,
                child: Container(
                    width: Utils().screenWidth(context)*0.6,
                    height: Utils().screenWidth(context)*0.6,
                    decoration: BoxDecoration(
                        color: Colors.white,
                        borderRadius: BorderRadius.circular(10),
                        border: Border.all(width: 1,color: JadeColors.blue_2)
                    ),
                    child: Stack(
                      alignment: Alignment.center,
                      children: [
                        QrImage(
                          padding: EdgeInsets.all(11.w),
                          data: qrStr,
                          version: QrVersions.auto,
                          size: Utils().screenWidth(context) * 0.6,
                        ),
                        Container(
                          width: 60.w,
                          height: 60.w,
                          decoration: BoxDecoration(
                              color: Colors.white,
                              borderRadius: BorderRadius.circular(5),
                              border: Border.all(width: 1.w,color:Colors.white)
                          ),
                          child: Utils().roundedImage(PathConfig.httpAppLogo, 5),
                        )
                      ],
                    )
                ),
            ),
            Container(
              margin: EdgeInsets.only(top: 40.w),
              height: 0.5,color: JadeColors.grey_13,
            ),
            Container(
              height: 92.w,
              child: Row(
                children: [
                  if(showCancel)
                    Expanded(child: GestureDetector(
                      child: Container(
                          color: Colors.transparent,
                          alignment: Alignment.center,
                          child: Text(S.current.quxiao,style: TextStyle(color: JadeColors.grey,fontSize: 34.sp,fontWeight: FontWeight.w300))
                      ),
                      onTap: (){
                        NavigatorUtil.pop();
                        if(cancelCallback != null){
                          cancelCallback();
                        }
                      },
                    )),
                  if(showCancel)
                    Container(width: 0.5,color: JadeColors.grey_13,height: double.infinity,),
                  Expanded(child: GestureDetector(
                    child: Container(
                      alignment: Alignment.center,
                      color: Colors.transparent,
                      child: Text(sureBtnText??S.current.close,style: TextStyle(color: sureBtnTextColor??Colors.blue,fontSize: 34.sp,fontWeight: FontWeight.w600),textAlign: TextAlign.center),
                    ),
                    onTap: () async {
                      _saveScreenshot(globalKey);
                      if(callback != null){
                        callback();
                      }
                    },
                  )),
                ],
              ),
            )
          ],
        ),
      )
  );
}

  Future<Uint8List> takeScreenshot(GlobalKey _globalKey) async {
  try {
    RenderRepaintBoundary boundary = _globalKey.currentContext.findRenderObject() as RenderRepaintBoundary;
    ui.Image image = await boundary.toImage(pixelRatio: 3.0); // 调整分辨率以适应高像素密度设备
    ByteData byteData = await image.toByteData(format: ui.ImageByteFormat.png);
    if (byteData != null) {
      Uint8List pngBytes = byteData.buffer.asUint8List();
      return pngBytes;
    }
  } catch (e) {
    print(e);
  }
  return null;
}

 _saveScreenshot(GlobalKey globalKey) async {
  Uint8List screenshotBytes = await takeScreenshot(globalKey);
  if (screenshotBytes != null) {
    final result = await ImageGallerySaver.saveImage(screenshotBytes);
    print('result= $result');// 打印保存结果
    esLoadingToast('已保存截图至本地');
  }else{
    esLoadingToast('截图保存失败');
  }
  NavigatorUtil.pop();
}

弹窗

 /*
  * 产品二维码弹窗
  * */
  Future<void> productQrCodeDialog(BuildContext context,{String descTitle,String subTitle,String desc,String qrStr,GlobalKey globalKey,Function callback,Function cancelCallback,bool showCancel = false,String sureBtnText,Color sureBtnTextColor}) async {
    showDialog(
        context: context,
        barrierDismissible: false,
        builder: (BuildContext context) {
          return productQrcodeDialog(context,descTitle: descTitle,subTitle: subTitle,desc: desc,qrStr: qrStr,globalKey: globalKey,showCancel: showCancel,sureBtnText: sureBtnText,sureBtnTextColor:sureBtnTextColor,callback: callback,cancelCallback : cancelCallback);
        });
  }

调用

GlobalKey _globalKey = new GlobalKey();
GestureDetector(
child:_btnView(),
onTap: (){
productQrCodeDialog(context,
   descTitle: '产品二维码',
   desc: '请保存下载该二维码并打印，随同产品一起寄送至站点。',
   qrStr: '二维码的内容',
   globalKey: _globalKey,
   showCancel: true,
   sureBtnText: '下载',
    sureBtnTextColor: JadeColors.grey_2,
    callback: (){}
  );
   }
}
)