objective-c - 对指向接口(interface) 'NSDate' 的指针进行算术运算，这在非脆弱 ABI 中不是常量大小

Question

下一个obj-c代码有问题错误。

if (fabs(originalLocation.timestamp - ((CLLocation *)[lastLocations objectAtIndex:i]).timestamp) > constAverageLocationTimeout) 
{ 
    //do 
}

xCode 发送错误:

error: Semantic Issue: Arithmetic on pointer to interface 'NSDate', which is not a constant size in non-fragile ABI

有什么想法吗？

Answer 1

如果你把它分解一点，你的程序(和编译器错误的位置)会更有意义。也许是这样的:

NSDate * orginalDate = originalLocation.timestamp;
CLLocation * lastLocation = [lastLocations objectAtIndex:i];
NSDate * lastDate = lastLocation.timestamp;

NSTimeInterval originalTime = [originalDate timeIntervalSinceReferenceDate];
NSTimeInterval lastTime = [lastDate timeIntervalSinceReferenceDate];
NSTimeInterval elapsed = fabs(originalTime - lastTime);

if (elapsed > constAverageLocationTimeout) {
  /* do */
}

具体来说，timestamp 是 NSDate 类型的属性，而不是 NSTimeInterval 等标量数。