UIProgressView进度更新在AlamoFire（异步）调用中非常慢 [英] UIProgressView progress update very slow within AlamoFire (async) call

问题描述

在AlamoFire获取请求中，我正在尝试更新进度栏。像这样：

Inside an AlamoFire get request I'm trying to update my progress bar. Like so:

alamofireManager.request(.GET, urlPath, parameters: params).responseJSON{(request,response,JSON,error) in
    ...<code here>...
    dispatch_async(dispatch_get_main_queue(), {
        NSNotificationCenter.defaultCenter().postNotificationName(LoginVCHideSpinnerAndShowProgressBarName as String, object: self)
    })
    ...<more code here>...
}

由于某些原因，这需要花费几秒钟的时间，如果我使用 dispatch_sync ，该应用程序似乎就此卡住了，但UI却没有冻结（活动指标微调器继续运行）。
我还想指出的是，一旦应用程序点击了此代码，它将继续执行后的代码，就好像它已被执行一样。然后大约在6秒钟后执行它，就好像没有在主线程上调用它一样。

For some reasons this takes a few seconds to execute and if I use dispatch_sync instead the app just seems to get stuck at that point but the UI doesn't freeze up (the activity indicator spinner keeps going). I also want to point out that once the app hits this code it continues on to the code after it as if its been executed. It then is executed about 6 seconds later as if it wasn't being called on the main thread.

我也只是尝试这样做而不是使用Notification。

I have also just simply tried doing this instead of using a Notification.

dispatch_async(dispatch_get_main_queue(), {
    loginVC.progressBar.hidden = false
    loginVC.indicator.hidden = true
    loginVC.progressBar.setProgress(0.1, animated: true)
})

这似乎比通知要慢。

我很困惑为什么会这样，因为我告诉它在主线程中进行更新。我也感到困惑，为什么通知实际上要快一些。

I am very puzzled to why this is happening since I am telling it to update in the main thread. I am also confused why the notification is actually a little bit faster.

推荐答案

在Alamofire中，有一种更好的方法。当数据任务上发生数据传输时，您可以使用 progress 闭包自动获取回调。这是来自README监视下载请求进度的示例。

There's a MUCH better way to do this in Alamofire. You can use the progress closure to automatically get a callback when a data transfer occurs on your data task. Here's an example from the README monitoring progress for a download request. The same applies for a data request.

let progressView = UIProgressView(progressViewStyle: .Bar)

let params = ["foo": "bar"]
let URLString = "http://httpbin.org/get"

let request = Alamofire.request(.GET, URLString, parameters: params)
request.progress { _, _, _ in
    progressView.setProgress(request.progress.fractionCompleted, animated: true)
}
request.responseJSON { request, response, json, error in
    println(request)
    println(response)
    println(json)
    println(error)
}

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