Question

我正在开发Flutter应用程序，该应用程序将Firebase用作后端。在我的Cloud Firestore中，我有两个集合：足球（包含一个文档）和即将到来的团队。
足球中文档的字段：

-字符串currentTeam2

-String即将出现的Team1

-String即将出现的Team2

-int team1Score

-int team2Score

即将到来的团队中的文档字段：

在足球文档中，将即将到来的Team1的值放入currentTeam1中，与团队2相同
从即将到来的团队中，复制球队并将值放入橄榄球文档的“即将到来的Team1”和“即将到来的Team2”字段中

为此，我相信第一步是从足球文档中获取即将到来的Team1和即将到来的Team2。为此，我编写了以下函数，该函数在相应按钮的onTap属性中分配：

void _nextMatch() {
    UpcomingMatch upcomingMatch;
    Firestore.instance
        .collection('football')
        .document("cMrD3OoOsWuzJmzlpfsr")
        .get()
        .then((DocumentSnapshot documentSnapshot) {
      if (documentSnapshot.exists) {
        upcomingMatch = UpcomingMatch(
            documentSnapshot.data["nextTeam1"].toString(),
            documentSnapshot.data["nextTeam2"].toString());
        print(documentSnapshot.data["nextTeam1"].toString());
        print(documentSnapshot.data["nextTeam2"].toString());
      }
    });
    if (upcomingMatch.upcomingTeam1.isNotEmpty && upcomingMatch.upcomingTeam2.isNotEmpty) {
      Firestore.instance
          .collection("football")
          .document("cMrD3OoOsWuzJmzlpfsr")
          .updateData({
        "currentTeam1": upcomingMatch.upcomingTeam1,
        "currentTeam2": upcomingMatch.upcomingTeam2,
      });
    }
  }

但是，我得到以下错误：

I/flutter ( 8687): The following NoSuchMethodError was thrown while handling a gesture:
I/flutter ( 8687): The getter 'upcomingTeam1' was called on null.
I/flutter ( 8687): Receiver: null
I/flutter ( 8687): Tried calling: upcomingTeam1
I/flutter ( 8687):
I/flutter ( 8687): When the exception was thrown, this was the stack:
I/flutter ( 8687): #0      Object.noSuchMethod (dart:core-patch/object_patch.dart:51:5)
I/flutter ( 8687): #1      _MainPageState._nextMatch (package:foci_dev/pages/main_page.dart:178:23)
I/flutter ( 8687): #2      _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:992:19)
I/flutter ( 8687): #3      _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:1098:38)
I/flutter ( 8687): #4      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:184:24)
I/flutter ( 8687): #5      TapGestureRecognizer.handleTapUp (package:flutter/src/gestures/tap.dart:524:11)
I/flutter ( 8687): #6      BaseTapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:284:5)
I/flutter ( 8687): #7      BaseTapGestureRecognizer.acceptGesture (package:flutter/src/gestures/tap.dart:256:7)
I/flutter ( 8687): #8      GestureArenaManager.sweep (package:flutter/src/gestures/arena.dart:158:27)
I/flutter ( 8687): #9      GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:224:20)
I/flutter ( 8687): #10     GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:200:22)
I/flutter ( 8687): #11     GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:158:7)
I/flutter ( 8687): #12     GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:104:7)
I/flutter ( 8687): #13     GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:88:7)
I/flutter ( 8687): #17     _invoke1 (dart:ui/hooks.dart:267:10)
I/flutter ( 8687): #18     _dispatchPointerDataPacket (dart:ui/hooks.dart:176:5)
I/flutter ( 8687): (elided 3 frames from dart:async)
I/flutter ( 8687):
I/flutter ( 8687): Handler: "onTap"
I/flutter ( 8687): Recognizer:
I/flutter ( 8687):   TapGestureRecognizer#acb21

如果我正确地解释了这一点，则意味着未分配即将发生的Match的即将出现的Team1属性。我尝试将函数转换为异步并在查询前添加await关键字，但这无济于事。感谢您提前提供答案！

Answer 1

将更新内容包含在then块中，以便futureMatch具有一个值：

void _nextMatch() {
  UpcomingMatch upcomingMatch;
  Firestore.instance
      .collection('football')
      .document("cMrD3OoOsWuzJmzlpfsr")
      .get()
      .then((DocumentSnapshot documentSnapshot) {
        if (documentSnapshot.exists) {
          upcomingMatch = UpcomingMatch(
              documentSnapshot.data["nextTeam1"].toString(),
              documentSnapshot.data["nextTeam2"].toString());
          print(documentSnapshot.data["nextTeam1"].toString());
          print(documentSnapshot.data["nextTeam2"].toString());
        }
        if (upcomingMatch.upcomingTeam1.isNotEmpty &&
          upcomingMatch.upcomingTeam2.isNotEmpty) {
            Firestore.instance
            .collection("football")
            .document("cMrD3OoOsWuzJmzlpfsr")
            .updateData({
              "currentTeam1": upcomingMatch.upcomingTeam1,
              "currentTeam2": upcomingMatch.upcomingTeam2,
            });
        }
      });
}

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