DispatchGroup等待Firestore查詢完成

我在單個用戶 tapGesture 中運行多個 Firestore 查詢，這要求我確保應用程式中同時運行的 Firestore 查詢最少到沒有。我已經閱讀

使用@Kiril S. 的回答，代碼已更正，如下所示。

class WorkoutViewController: UIViewController {

let dispatchGroup = DispatchGroup()


alert.addAction(UIAlertAction(title: "Select", style: .default, handler: { [self]_ in
            
            dispatchGroup.enter()
            
            DispatchQueue.main.async {
                print("Firestore Sequence 2 Initiated")
                startActivityIndicator()
                
                if let user = Auth.auth().currentUser {
                    let userID = user.uid
                    
                    db.collection("user").whereField("author_uid", isEqualTo: userID).getDocuments { snapshot, error in
                        
                        if error == nil && snapshot != nil {
                            
                            for document in snapshot!.documents {
                            
                            let docID = document.documentID
                            
                            db.collection("user")
                                .document(docID)
                                .setData(["selectedWorkoutID" : workoutRow.workoutId], merge: true)
                                    
                            print("Firestore Sequence 2 Success - user selectedWorkoutID updated")
                                
                            }
                        }
                        
                        
                        if let user = Auth.auth().currentUser {
                            let userID = user.uid
                            checkAndCreateUserWorkoutProfile(selectedWorkout: workoutRow, userID: userID)
                         dispatchGroup.leave()
                        }
                    }
                }
            }

            dispatchGroup.notify(queue: .main) {
                print("Firestore Sequence 4 Initiated")
                print("Firestore Sequence 5 Initiated - Create/Read User Specific Dayprogram data")
                }

        }))

func checkAndCreateUserWorkoutProfile(selectedWorkout: Workout, userID: String) {

        print("Firestore Sequence 3 Initiated - createORread user specific workout profile")
        
        dispatchGroup.enter()
        
        db.collection("Workout")
            .whereField("workoutId", isEqualTo: selectedWorkout.workoutId)
            .whereField("userID", isEqualTo: userID)
            .getDocuments() { (querySnapshot, err) in
                
                if querySnapshot?.count == 0 {

                    var ref: DocumentReference? = nil
                  
                    ref = self.db.collection("Workout").addDocument(data:
                        [
                        "author_uid": selectedWorkout.author_uid!,
                        "workoutId": selectedWorkout.workoutId,
                        "userID": userID
                        ])

                     { err in
                        if let err = err {
                            print("Error adding user specific workout profile: \(err)")
                            self.dispatchGroup.leave()
                        } else {
                            print("Firestore Sequence 3 Success - User specific workout profile added/created with ID: \(ref!.documentID)")
                            self.dispatchGroup.leave()
                        }
                    }     
                }      
            }
        }

Xcode 控制臺顯示更正的代碼/查詢序列。

uj5u.com熱心網友回復：

所以基本上現在會發生什么：

• 警報動作開始
• 創造 let dispatchGroup = DispatchGroup()
• 進入那個組
• 離開小組==>dispatchGroup.notify開火
• checkAndCreateUserWorkoutProfile 啟動，創建自己的調度組等等（已經錯了，沒關系）

所以你有兩個問題：

1. 您必須有 1 個調度組，而不是每個功能都有一個單獨的組。所以轉到let dispatchGroup = DispatchGroup()類成員級別，這樣兩個函式都在同一個調度組中。

2. 并且您checkAndCreateUserWorkoutProfile需要在前一個呼叫離開之前進入調度組 。所以順序應該改為

   if let user = Auth.auth().currentUser {
       let userID = user.uid
       checkAndCreateUserWorkoutProfile(selectedWorkout: workoutRow, userID: userID)
   }
   dispatchGroup.leave()
   

那樣：

• 警報動作開始
• 進入定義為班級成員的組
• Calls checkAndCreateUserWorkoutProfile，它進入同一個調度組并開始它的異步呼叫
• 警報動作離開組（但通知不會觸發，因為還checkAndCreateUserWorkoutProfile沒有離開組）
• checkAndCreateUserWorkoutProfile最終離開小組 ==>dispatchGroup.notify開火

標籤：迅速 谷歌云firestore 工具包 完成处理程序 调度组

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