objective-c - 减去定义为常量的两个浮点数时的意外结果

Question

我正在尝试调整框架。我有两个常量定义为浮点数 -viewTotalHeightExpanded和viewTotalHeight. 我将两者相减得到differenceY.

  CGFloat differenceY = viewTotalHeightExpanded - viewTotalHeight;
  NSLog(@"viewTotalHeightExpanded = %f", viewTotalHeightExpanded);
  NSLog(@"viewTotalHeight = %f", viewTotalHeight);
  NSLog(@"differenceY = %f", differenceY);

日志内容如下：

2013-08-24 12:30:48.305 WS[25737:c07] viewTotalHeightExpanded = 406.000000
2013-08-24 12:30:48.305 WS[25737:c07] viewTotalHeight = 366.000000
2013-08-24 12:30:48.306 WS[25737:c07] differenceY = 680.000000

为什么differenceY不是40？

编辑

这是如何定义的viewTotalHeight：viewTotalHeightExpanded

#define likeBarHeight 20.0f
#define viewTotalHeight likeBarY+likeBarHeight+sortBarHeight

所有其他链式常量，例如likeBarY和sortBarHeight被定义为类似于likeBarHeight.

Answer 1

这就是你正在做的事情：

CGFloat differenceY = viewTotalHeightExpanded - viewTotalHeight;

这是因为 viewTotalHeight 是 likeBarY+likeBarHeight+sortBarHeight 转换为

CGFloat differenceY = viewTotalHeightExpanded -likeBarY+likeBarHeight+sortBarHeight

所以试试这个：

 CGFloat differenceY = (viewTotalHeightExpanded) - (viewTotalHeight);

或者甚至更好地使 viewTotalHeight 可以在没有括号的情况下重复使用

#define viewTotalHeight (likeBarY+likeBarHeight+sortBarHeight)