在使用操作队列时更新 UI

Question

我有一个操作队列设置如下：

let queue = OperationQueue()
queue.name = "com.company.myQueue"
queue.qualityOfService = .userInitiated
queue.maxConcurrentOperationCount = 64
...
var current = 0
var totalCount = someArray.count
for i in someArray {
... 
let op = BlockOperation {
... // do some database queries
current += 1
}
op.completionBlock = {
DispatchQueue.main.async {
let nData: [String: CGFloat] = ["value": CGFloat(current/totalCount)]
NotificationCenter.default.post(name:Notification.Name(rawValue: "update"), object: nil, userInfo: nData)
}
queue.addOperation(op)
}

在我的ViewController中，我监听通知并使用百分比更新UILabel。问题是虽然我没有得到任何中间值...一旦完成所有操作，它就会从直接0跳到100。

我做错了什么？

谢谢

Answer 1

问题是CGFloat(current / totalCount).它首先执行整数数学运算，然后将其转换为浮点数。你应该把它翻过来CGFloat(current) / CGFloat(totalCount).

Answer 2

您可以直接在 op.completionBlock 中移动通知发送函数(无需在主线程中调度它(。

编辑(评论(：

let queue = OperationQueue()
queue.name = "com.company.myQueue"
queue.qualityOfService = .userInitiated
queue.maxConcurrentOperationCount = 64
let array = ["", "", "", "", "", ]
var current = 0
var totalCount = array.count
for _ in array {
let op = BlockOperation { current += 1 ; print(current) }
op.completionBlock = {
DispatchQueue.main.async {
NotificationCenter.default.post(name: Notification.Name(rawValue: "update"), object: nil, userInfo: ["value": CGFloat(current / totalCount)])
}
}
queue.addOperation(op)
}
NotificationCenter.default.addObserver(forName: Notification.Name(rawValue: "update"), object: nil, queue: nil) { (notification) in
print(notification.userInfo)
}

编辑2(评论(： 您应该在除以它们之前通过浮动转换当前和总计数来制作百分比。

CGFloat(current) / CGFloat(totalCount)
'''