我想按顺序快速运行for循环，DispatchGroup会将它们一起触发，因此我想使用DispatchQueue和DispatchSemaphore达到我的目标。我无法使程序正常运行，如何强迫他们等待并逐一运行？
let dispatchGroup = DispatchGroup()
let dispatchQueue = DispatchQueue(label: "taskQueue")
let dispatchSemaphore = DispatchSemaphore(value: 1)
for c in self.categories {
dispatchSemaphore.wait()
dispatchQueue.async(group: dispatchGroup) {
if let id = c.categoryId {
dispatchGroup.enter()
self.downloadProductsByCategory(categoryId: id) { success, data in
if success, let products = data {
self.products.append(products)
}
dispatchSemaphore.signal()
dispatchGroup.leave()
}
}
}
}
dispatchGroup.notify(queue: dispatchQueue) {
self.refreshOrderTable { _ in
self.productCollectionView.reloadData()
NVActivityIndicatorPresenter.sharedInstance.stopAnimating()
}
}
感谢Palle，这是我的最终代码：
let dispatchGroup = DispatchGroup()
let dispatchQueue = DispatchQueue(label: "taskQueue")
let dispatchSemaphore = DispatchSemaphore(value: 0)
dispatchQueue.async {
for c in self.categories {
if let id = c.categoryId {
dispatchGroup.enter()
self.downloadProductsByCategory(categoryId: id) { success, data in
if success, let products = data {
self.products.append(products)
}
dispatchSemaphore.signal()
dispatchGroup.leave()
}
dispatchSemaphore.wait()
}
}
}
dispatchGroup.notify(queue: dispatchQueue) {
DispatchQueue.main.async {
self.refreshOrderTable { _ in
self.productCollectionView.reloadData()
}
}
}
您可以将整个循环放在一个块中，而不仅仅是将下载功能放在一个块中：
dispatchQueue.async {
for c in self.categories {
if let id = c.categoryId {
self.downloadProductsByCategory(categoryId: id) { success, data in
if success, let products = data {
self.products.append(products)
}
dispatchSemaphore.signal()
}
dispatchSemaphore.wait()
}
}
}
您可以使用compactMap解开产品ID来简化代码：
for id in self.categories.compactMap({$0.categoryId}) { ... }
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我来说两句