ios - 在后台更新 NSDate 和 NSString

Question

美好的一天!我只想问一下我如何在后台更新这些代码？

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"yyyy/MM/dd  hh:mm:ss"];
self.txtTimestamp.text = [formatter stringFromDate:[NSDate date]];

NSString *buyUrl = @"https://docs.google.com/spreadsheet/pub?key=0AkgWFqjLQz0TdHdMQzBsc1lhaGFPZEFCYXBLWEt1Q0E&single=true&gid=3&output=txt";
NSString *buyFile= [NSString stringWithContentsOfURL:[NSURL URLWithString:buyUrl] encoding:NSUTF8StringEncoding error:nil];
self.txtBuydata.text = buyFile;

如果应用程序是新打开的，则日期和时间正在更新，因为它在 ViewDidLoad 和 NSString 代码中。现在，如何每分钟在后台更新 NSDate 和 NSString？所以即使应用程序在后台，NSSting 也会每分钟更新一次，即使应用程序在后台或打开。非常感谢!

Answer 1

您需要使用NSTimer 重复执行一个 Action 。

示例:

- (void)viewDidLoad {
    //...
    //declare "NSTimer *timerTest;" in the .h
    timerTest = [NSTimer scheduledTimerWithTimeInterval:1.0
                                                 target:self
                                               selector:@selector(doThisRepeatedly:)
                                               userInfo:nil
                                                repeats:YES];
    //...
}

- (void)doThisRepeatedly:(NSTimer *)sender
{
    NSLog(@"%@",sender);
    //...
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"yyyy/MM/dd  hh:mm:ss"];
    self.txtTimestamp.text = [formatter stringFromDate:[NSDate date]];
    //...

    //fyi: if you want to stop the timer from within this method (generally in a condition)
    //then use the following commented line:
    //[sender invalidate];
}

要从另一个方法中停止计时器，然后通过它的对象名称引用它并简单地:

[timerTest invalidate];