ios - 等待一个 block 加载，然后再加载更多

Question

我正在构建一个应用程序，我需要在其中分 block 加载数据，我的意思是先加载 5 个项目，然后继续加载另外 5 个，但我不知道该怎么做。目前我整理了我的项目列表，所以我得到了一个列表列表，每个列表有 5 个项目。现在，for 循环刚刚触发请求，但我想等待响应，然后在 for 循环中继续。

我使用 alamofire，我的代码如下所示。

private func requestItemsForField(items: [Item], completion: @escaping (_ measurements: Array<Measurement>?, _ success: Bool) -> ()) {
    let userPackageId = UserManager.instance.selectedUserPackage.id
    let params = ["userPackageId": userPackageId]

    for field in fields {
    let url = apiURL + "images/\(field.id)"

    let queue = DispatchQueue(label: "com.response-queue", qos: .utility, attributes: [.concurrent])
    Alamofire.request(url, method: .get, parameters: params, headers: headers()).responseArray(queue: queue, completionHandler: { (response: DataResponse<[Item]>) in

        if let items = response.result.value as [Item]? {
            NotificationCenter.default.post(name: NSNotification.Name(rawValue: "itemsLoadedNotification"), object: nil)
            completion(items, true)
        }
        else {
            print("Request failed with error: \(response.result.error)")
            completion(nil, false)
        }
    })
    }
}

这是我整理列表并将其传递给上面的地方。

 private func fetchAllMeasurements(completion: @escaping (_ measurements: [Item]?, _ done: Bool) -> ()) {
    let fieldSet = FieldStore.instance.data.keys
    var fieldKeys = [Item]()

    for field in fieldSet {
        fieldKeys.append(field)
    }

    // Create chunks of fields to load
    let fieldChunks = fieldKeys.chunkify(by: 5)

    var measurementsAll = [Measurement]()
    for fields in fieldChunks {
        requestItemsForField(fields: fields, completion: { (measurements, success) in
            if let currentMeasurement = measurements {
                measurementsAll.append(contentsOf: currentMeasurement)
            }
                completion(measurementsAll, true)
            }
        })
    }
}

Answer 1

您需要根据您的请求获得您将拥有的测量数量(例如服务器有 34 个测量)，然后编写类似的代码

var serverMeasurementsCount = 1 //should be for first request

func requestData() {
    if self.measurements.count < self.serverMeasurementsCount {
        ...requestdata { data in
            self.serverMeasurementsCount = data["serverMeasurementsCount"]
            self.measurements.append(..yourData)
            self.requestData()
        }
    }

或者不在completion handler或其他地方调用requestData

编辑:稍微修正了代码(serverMeasurementsCount = 1)