好的-找到了答案.需要将其放置在不同的线程中，该线程允许UI在执行完线程功能后立即进行更新:

Okay - found the answer. It needs to be placed inside a different thread that allows the UI to update as soon as execution of thread function complete :

 DispatchQueue.main.async {
    // Update UI
 }

迅速版本< 3

dispatch_async(dispatch_get_main_queue(){
    // code here
})

Objective-C版本

dispatch_async(dispatch_get_main_queue(), ^{
    // code here
});