ios - 在 Swift 3 中访问闭包外的数组
<p><p>我有这个闭包,我用它来填充我的数组和字典。但是,当我尝试在函数之外使用它时,它是空的。我知道这个闭包在异步线程上工作,所以假设我在填充之前尝试访问该变量是否正确?结果,我得到一个空数组。这是我的代码。</p>
<pre><code>class HomeCollectionViewController: UICollectionViewController, UICollectionViewDelegateFlowLayout, UISearchBarDelegate, UIGestureRecognizerDelegate {
var entries = ()
var entryIDS =()
var searchController: UISearchController!
override func viewDidLoad() {
super.viewDidLoad()
// Register cell classes
self.collectionView!.register(DiaryCell.self, forCellWithReuseIdentifier: "homeCell")
collectionView?.backgroundColor = UIColor.white
navigationController?.hidesBarsOnSwipe = true
if let userID = FIRAuth.auth()?.currentUser?.uid {
FirebaseService.service.getUserEntriesRef(uid: userID).observe(.value, with: { (snapshot) in
let enumerator = snapshot.children
while let entry = enumerator.nextObject() as? FIRDataSnapshot {
weakSelf?.entryIDS.append(entry.key)
weakSelf?.entries = DiaryEntry(snapshot: entry)
}
weakSelf?.entryIDS.reverse()
weakSelf?.collectionView?.reloadData()
})
print("Entries: \(entryIDS.count) ")
}
// Do any additional setup after loading the view.
}
</code></pre>
<p>处理这种多线程执行的最佳方法是什么?</p></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>使用 <a href="https://developer.apple.com/reference/dispatch/dispatchgroup" rel="noreferrer noopener nofollow">Dispatch Groups</a>跟踪您完成将所有元素附加到数组的时间,然后进行 <code>notify</code> 回调,当它们全部添加时会自动调用。</p>
<pre><code>class HomeCollectionViewController: UICollectionViewController, UICollectionViewDelegateFlowLayout, UISearchBarDelegate, UIGestureRecognizerDelegate {
var entries = ()
var entryIDS =()
let dispatchGroup = DispatchGroup()
var searchController: UISearchController!
override func viewDidLoad() {
super.viewDidLoad()
// Register cell classes
self.collectionView!.register(DiaryCell.self, forCellWithReuseIdentifier: "homeCell")
collectionView?.backgroundColor = UIColor.white
navigationController?.hidesBarsOnSwipe = true
self.dispatchGroup.enter()
if let userID = FIRAuth.auth()?.currentUser?.uid {
FirebaseService.service.getUserEntriesRef(uid: userID).observe(.value, with: { (snapshot) in
let enumerator = snapshot.children
while let entry = enumerator.nextObject() as? FIRDataSnapshot {
weakSelf?.entryIDS.append(entry.key)
weakSelf?.entries = DiaryEntry(snapshot: entry)
}
self.dispatchGroup.leave()
})
self.dispatchGroup.notify(queue: DispatchQueue.main, execute: {
print("Entries: \(entryIDS.count) ")
weakSelf?.entryIDS.reverse()
weakSelf?.collectionView?.reloadData()
})
}
// Do any additional setup after loading the view.
}
</code></pre>
<p>我还建议只使用 <code>self</code> 而不是 <code>weakSelf?</code>。</p></p>
<p style="font-size: 20px;">关于ios - 在 Swift 3 中访问闭包外的数组,我们在Stack Overflow上找到一个类似的问题:
<a href="https://stackoverflow.com/questions/42015954/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/42015954/
</a>
</p>
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