失败的断言：第 373 行 pos 7：'pixels == null || (minScrollExtent != null && maxScrollExtent != null)'

问题描述

我是Flutter的新手，所以当我尝试从api获取图像并将它们添加到列表中然后使用时，我无法解决页面视图异常列表中的 foreach 循环以在 carousel pro

中显示图像

我的代码是--

 if (widget.user_id != null) {
      body = jsonEncode(<String,dynamic>{
        'respObj': {
          "Id": widget.user_id,},});
    } else {
      body = jsonEncode(<String,dynamic>{});
    }
 final http.Response response = await http.post(
      'api url',headers: <String,String>{
        'Content-Type': 'application/json; charset=UTF-8',body: body,);
    var res = json.decode(response.body);
    if (response.statusCode == 200) {
      res["resplist"].forEach((element){
        setState(() {
          images.add(element["categoryBanner"]);
        });
      });
      images.forEach((element) {
        setState(() {
          _img.add(NetworkImage(element));
        });
      });
    } else {
      images==null;
    }

    Widget imageCrousel = Container(
      height: 140.0,child: Carousel(
        indicatorBgPadding: 5.0,dotIncreasedColor: Colors.red,dotColor: Colors.white,BoxFit: BoxFit.cover,images:_img==null?
        [Assetimage('assets/defimg.jpg')]:_img,autoplay: false,animationCurve: Curves.fastOutSlowIn,animationDuration: Duration(milliseconds: 1000),),);

异常---

Page value is only available after content dimensions are established.
'package:Flutter/src/widgets/page_view.dart':
Failed assertion: line 373 pos 7: 'pixels == null || (minScrollExtent != null && maxScrollExtent != null)'

解决方法

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Flutter - PageController error: Page value is only available after content dimensions are established.