我的应用程序在到达代码的这一部分时会冻结。我试图以一半秒的延迟递增一个数字，然后将其打印到屏幕上。所以标签文本会变成1，然后是2，然后是3，等等。我把这个代码扔进游乐场，DispatchQueue似乎无限上升。感谢。
var percentage = 0
func incrementLabel (amount: Int){
var count = 0
while count <= amount{
DispatchQueue.main.asyncAfter(deadline: .now() + 0.5, execute: {
percentage += 1
count += 1
})
}
}
incrementLabel(amount: 10)
print(percentage)
答案 0 :(得分：0)
以下是您可以使用的替代解决方案，而不是Tier3Toolbox.EARTH_RADIUS = 6378137; /* Equitorial Radius instead of 6371000 */
Tier3Toolbox.toRad =
function (num) {
return num * Math.PI / 180;
};
Tier3Toolbox.calculateDistance =
function(lat1, lon1, lat2, lon2){
var dLat = this.toRad(lat2 - lat1);
var dLon = this.toRad(lon2 - lon1);
var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) + Math.cos(this.toRad(lat1)) *
Math.cos(this.toRad(lat2)) * Math.sin(dLon / 2) * Math.sin(dLon / 2);
var distance = this.EARTH_RADIUS * 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
return distance;
}
：
DispatchQueue这在Swift中使用var percentage = 0
var counter = 0
var timer: Timer?
func incrementLabel(amount: Int) {
counter = amount
timer = Timer.scheduledTimer(timeInterval: 0.5, target: self, selector: #selector(self.updateDelay), userInfo: nil, repeats: true)
}
@objc func updateDelay() {
if (counter > 0) {
counter -= 1
percentage += 1
} else {
timer.invalidate()
timer = nil
}
}
incrementLabel(amount: 10)
print(percentage)
。