尝试比较DocumentID和List中Firestore DocumentReference对象的ID。并遇到了这种奇怪的行为。我想从列表中获取正确的对象。我究竟做错了什么?
DocumentReference _resolveReferenceFromID(
List<DocumentReference> references, String documentID) {
references.forEach((element) {
print('element id: ${element.documentID}');
print('document id: $documentID');
if (element.documentID == documentID) {
return element;
}
});
print('something is wrong here');
return null;
}
这是一个输出:
element id: W24buSwq7cYOahJz6Gdq
document id: W24buSwq7cYOahJz6Gdq
element id: cBOIXvebYYIpox5cAcct
document id: W24buSwq7cYOahJz6Gdq
something is wrong here
扑--version:
Flutter 1.22.0-2.0.pre.36 • channel master • https://github.com/flutter/flutter.git
Framework • revision d30e36ba8c (6 days ago) • 2020-08-21 22:36:03 -0400
Engine • revision d495da20d0
Tools • Dart 2.10.0 (build 2.10.0-49.0.dev)
扑医生:
Doctor summary (to see all details, run flutter doctor -v):
[√] Flutter (Channel master, 1.22.0-2.0.pre.36, on Microsoft Windows [Version 10.0.18362.1016], locale en-US)
[√] Android toolchain - develop for Android devices (Android SDK version 30.0.1)
[√] Chrome - develop for the web
[√] Android Studio (version 4.0)
[√] VS Code (version 1.48.2)
[√] Connected device (3 available)
• No issues found!
您正在forEach
用来遍历元素。在return element
里面forEach
只能从函数,而不是从周围的函数参数返回_resolveReferenceFromID
功能。
更改为:
DocumentReference _resolveReferenceFromID(
List<DocumentReference> references, String documentID) {
for (var element in references) {
print('element id: ${element.documentID}');
print('document id: $documentID');
if (element.documentID == documentID) {
return element;
}
}
print('something is wrong here');
return null;
}
然后,return element;
将从所需的函数返回。
另请参阅:https : //dart.dev/guides/language/effective-dart/usage#avoid-using-iterableforeach-with-a-function-literal
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