iphone - 为什么这段 Objective C 代码会泄漏内存？

Question

已更新

我在 Objective C 中有这个方法:

-(NSDate*)roundTo15:(NSDate*)dateToRound {
    int intervalInMinute = 15;
    // Create a NSDate object and a NSDateComponets object for us to use
    NSDateComponents *dateComponents = [[NSCalendar currentCalendar] components:NSMinuteCalendarUnit fromDate:dateToRound];

    // Extract the number of minutes and find the remainder when divided the time interval
    NSInteger remainder = [dateComponents minute] % intervalInMinute; 
    // gives us the remainder when divided by interval (for example, 25 would be 0, but 23 would give a remainder of 3

    // Round to the nearest 5 minutes (ignoring seconds)
    if (remainder >= intervalInMinute/2) {
        dateToRound = [dateToRound dateByAddingTimeInterval:((intervalInMinute - remainder) * 60)]; // Add the difference
    } else if (remainder > 0 && remainder < intervalInMinute/2) {
        dateToRound = [dateToRound dateByAddingTimeInterval:(remainder * -60)]; // Subtract the difference
    }

    return dateToRound;
}

这就是我调用该方法的方式:

item.timestamp = 
    [self roundTo15:[[NSDate date] dateByAddingTimeInterval:60 * 60]];

当执行以下行时，Instruments 说我泄漏了 NSDate 对象:

dateToRound = [dateToRound dateByAddingTimeInterval:(remainder * -60)];

所以这是我的项目对象，我需要使用新的更正的 NSDate 进行更新。我尝试创建一个 roundedDate 并像这样返回它:return [roundedDate autorelease];，但随后出现了错误的访问错误。

Answer 1

问题在于 dateToRound 作为对一个对象的引用传入，而您将其设置为对另一个对象的引用。原始对象现已被废弃并已泄露。

您应该创建一个新的 NSDate * 并返回它，而不是重新分配 dateToRound。

示例代码:

-(NSDate*)roundTo15:(NSDate*)dateToRound {
    int intervalInMinute = 15;
    // Create a NSDate object and a NSDateComponets object for us to use
    NSDateComponents *dateComponents = [[NSCalendar currentCalendar] components:NSMinuteCalendarUnit fromDate:dateToRound];

    // Extract the number of minutes and find the remainder when divided the time interval
    NSInteger remainder = [dateComponents minute] % intervalInMinute; // gives us the remainder when divided by interval (for example, 25 would be 0, but 23 would give a remainder of 3

    // Round to the nearest 5 minutes (ignoring seconds)
    NSDate *roundedDate = nil;
    if (remainder >= intervalInMinute/2) {
        roundedDate = [dateToRound dateByAddingTimeInterval:((intervalInMinute - remainder) * 60)]; // Add the difference
    } else if (remainder > 0 && remainder < intervalInMinute/2) {
        roundedDate = [dateToRound dateByAddingTimeInterval:(remainder * -60)]; // Subtract the difference
    } else {
        roundedDate = [[dateToRound copy] autorelease];
    }

    return roundedDate;
}