比较两个NSDates在iPhone [英] Compare two NSDates in iPhone

问题描述

我是iPhone开发者的新手，

I am new to iPhone developer,

我想比较两个日期，第一个日期将来自数据库let say， newDate ，第二个是今天的日期，

i want to compare two Dates, first date will come from Database let say, newDate and second is todays date,

如果今天大于 newDate

这是我的代码段，

NSString *newDate = [formatter stringFromDate:st];
NSDate *today=[[NSDate alloc]init];

if ([today compare:newDate] == NSOrderedDescending)
{
    NSLog(@"today is later than newDate");        
}
else if ([today compare:newDate] == NSOrderedAscending)
{
    NSLog(@"today is earlier than newDate");        
}
else
{
    NSLog(@"dates are the same");        
}

但是崩溃，并且编译时也会在此显示警告 [today compare：newDate]

but it crashes, and while compiling it also shows me warning here [today compare:newDate]

任何帮助将不胜感激。 $ b

推荐答案

问题是，你要比较字符串和日期。如果你看看 newDate ，你会看到它的 NSString 而不是 NSDate 。如果在 NSDate 上使用 compare：方法，两个对象必须 NSDate 的。看看你的代码，看起来 st 是 NSDate 对应于 newDate （虽然你的命名看起来有点奇怪），尝试今天而不是 newDate

The problem is, that you are comparing strings and dates. If you look at newDate, you will see that its a NSString and not a NSDate. If you use the compare: method on NSDate, both objects have to be NSDate's. Looking at your code, it looks like st is the NSDate corresponding to newDate (although your naming seems a bit odd), try today with it instead of newDate

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