问题描述
我尝试查找此内容，但是找不到停止执行 observe 类型的firebase查询的方法.每次引用更新数据库时，Observe都会进行回调并保持运行.但是我想在视图消失时停止运行该回调，并在视图出现时再次开始运行查询.
I tried looking this up but could not find a way to stop the execution of a firebase query of type observe. Observe takes a call back and keeps running it every time the database is updated at a reference. But I want to stop this callback from running when the view disappears and again start running the query when view will appear.
这就是我想要做的.不幸的是，observe函数返回的是int，而不是可用于停止查询执行的任何处理程序.
So this is what I want to do. Unfortunately the observe functions returns an int and not any handler that can be used to stop the query's excution.
func viewWillDissappear(animated: Bool) {
...
stopQuery()
}
func viewWillAppear(animated: Bool) {
...
startQuery()
}
func startQuery() {
Database.database().reference().observe(.value) { (snapshot) in
//Rest of callback to be executed only when view will appear and is visible
}
}
func stopQuery() {
//Stop query callback execution started by startQuery
}
注意:我不希望依赖于使用vairble来检查视图是否可见并跳过回调执行的答案.我想完全取消当前正在运行的查询，并在下一次显示视图时重新启动它.
Note: I don't want answers that rely on using a vairble to check if view is visible and skip the callback execution. I want to compeletly cancel the currently running query and restart it the next time view will appear.
推荐答案
Swift中的句柄 FIRDatabaseHandle 又名 DatabaseHandle 被定义为:
The handle FIRDatabaseHandle aka DatabaseHandle in Swift is defined as:
typedef NSUInteger FIRDatabaseHandle NS_SWIFT_NAME(DatabaseHandle);
因此，您实际上对这是一个整数是正确的.但是最好将返回的句柄存储到一个强变量句柄中，以便可以从 stopQuery()函数中停止/删除观察者.
Therefore, you're actually correct about this being an integer. But it's best if you store the returned handle to a strong variable handle, so that you can stop/remove the observer from your stopQuery() function.
像这样:
// MARK: - Properties
private var handle: DatabaseHandle?
// MARK: - Functions
...
...
func startQuery() {
handle = Database.database().reference().observe(.value) { (snapshot) in
//Rest of callback to be executed only when view will appear and is visible
}
}
func stopQuery() {
//Stop query callback execution started by startQuery.
Database.database().reference()
.removeObserver(withHandle: handle)
}
请记住，您需要跟踪整个路径(即特定的孩子).否则，您可能无法删除观察者.
Remember that you need to track your whole path (ie specific child)., otherwise you might fail in removing your observer.
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