admob横幅不会显示在动态列表中

Question

我试图在每3个帖子之间显示一个bannerAd。但广告并没有出现。我想，这个列表可能是空的，因为这个列表是根据用户喜欢和保存的帖子构建的列表。

@override
Widget build(BuildContext context) {
return Expanded(
child: ListView(
padding: EdgeInsets.symmetric(horizontal: 10.0),
children: [
StreamBuilderWrapper(
shrinkWrap: true,
stream: postRef
.where("bookmarks",
arrayContains: FirebaseAuth.instance.currentUser.uid)
.orderBy('timestamp', descending: true)
.snapshots(),
physics: NeverScrollableScrollPhysics(),
itemBuilder: (_, DocumentSnapshot snapshot) {
internetChecker(context);
Review posts = Review.fromJson(snapshot.data());
return Padding(
padding: const EdgeInsets.only(bottom: 10.0),
child: Posts(post: posts),
);
},
),
ListView.builder(
scrollDirection: Axis.vertical,
shrinkWrap: true,
itemBuilder: (context, index) {
return Column(
children: [
if (index % 3 == 0 && index != 0)
AdWidget(ad: ad)
],);})
]));
}

这是我第一次使用flutter，我对编码还是个新手。我正在尝试显示横幅广告，但是，它们没有显示，也没有显示日志。这可能是由于我的渲染错误：

The following _CastError was thrown during paint():
Null check operator used on a null value
The relevant error-causing widget was: 
ListView 
When the exception was thrown, this was the stack: 
#0      RenderViewportBase._paintContents 
(package:flutter/src/rendering/viewport.dart:653:25)
#1      RenderViewportBase.paint 
(package:flutter/src/rendering/viewport.dart:645:7)
#2      RenderObject._paintWithContext 
(package:flutter/src/rendering/object.dart:2317:7)
#3      PaintingContext._repaintCompositedChild 
(package:flutter/src/rendering/object.dart:139:11)
#4      PaintingContext.repaintCompositedChild 
(package:flutter/src/rendering/object.dart:100:5)
...
The following RenderObject was being processed when the exception was 
fired: 
RenderViewport#ae00e
...  needs compositing
...  parentData: <none> (can use size)
...  constraints: BoxConstraints(w=360.0, h=507.0)
...  layer: OffsetLayer#0dfc7 DETACHED
...    engine layer: Null#007db
...    offset: Offset(0.0, 0.0)
...  size: Size(360.0, 507.0)
...  axisDirection: down
...  crossAxisDirection: right
...  offset: ScrollPositionWithSingleContext#1c5d2(offset: 0.0, range: 
null..null, viewport: 507.0, ScrollableState, 
AlwaysScrollableScrollPhysics 
-> ClampingScrollPhysics -> RangeMaintainingScrollPhysics, 
IdleScrollActivity#40f4c, ScrollDirection.idle)

我对小部件和视图感到困惑。请帮帮我！非常感谢。

Answer 1

我不清楚你在做什么，我认为你这样做是错误的，我编辑了整个代码，这可能会有所帮助。

@override
Widget build(BuildContext context) {
return Expanded(
child: StreamBuilder(
stream: postRef
.where("bookmarks",
arrayContains: FirebaseAuth.instance.currentUser!.uid)
.orderBy('timestamp', descending: true)
.snapshots(),

builder: (_, DocumentSnapshot snapshot) {
if (snapshot.hasData) {

return ListView.separated(itemCount: snapshot.data.docs.length,
itemBuilder: (
context,
index,
) {
internetChecker(context);
Review posts = Review.fromJson(snapshot.data());
return Padding(
padding: const EdgeInsets.only(bottom: 10.0),
child: Posts(post: posts),
);
}, separatorBuilder: (context, index) {
if (index % 3 == 0 && index != 0)
return
AdWidget(ad: ad);
}, );
}else if (snapshot.hasError) {
return Center(
child:  Text("error"),

);
} else {
return  Center(
child:  Text("loading"),

);
}
},
),);