Question

对不起，这可能是一个菜鸟问题，但我正在使用CoreLocation而且这很难过。

我正在使用此站点上推荐的单例查找currentLocation，当我获取currentLocation对象时，它返回true为非零检查。但是，当我尝试打印其描述时，它会抛出EXC_BAD_ACCESS。

//WORKS Current location 8.6602e-290
NSLog(@"Current location %g",currLoc);

//DOESN'T WORK
NSLog(@"Current location %@",[currLoc description]);

//DOESN'T WORK - Is this causing the description to fail as well?
NSLog(@"Current location %g",currLoc.coordinate.latitude);

为什么我能看到第一个而不是其他的东西？顺便说一句，这是在3.1.2模拟器上运行谢谢。

Answer 1

currLoc.coordinate.latitude类型为double ...如果％g无效，您可以使用％f

NSLog(@"Current location %f",currLoc.coordinate.latitude);

Answer 2

currLoc 可能会为返回 TRUE 而非检查。但是可能存在释放对象（悬空指针）的机会，这将通过零检查条件。这可能是你的问题。

不要直接使用 currLoc成员，而是使用Accessor for currLoc 。这将解决您的问题：）

Answer 3

// malformed: %g format specifier expects type
// double, you're passing an objc object.
// sending arguments through (...) with the
// invalid types/widths is a near certain way
// to crash an app, and the data will be useless
// to the function called (NSLog in this case)
NSLog(@"Current location %g",currLoc);

// try running the app with zombies enabled.
// in short, enabling zombies (NSZombiesEnabled)
// is a debugging facility to determine whether
// you use an objc object which would have been freed.
NSLog(@"Current location %@",[currLoc description]);

// as long as currLoc is a pointer to a valid (non-freed)
// objc object, then this should be fine. if it is not valid
NSLog(@"Current location %g",currLoc.coordinate.latitude);

CLLocation不是nil但是尝试将其打印出来会抛出EXC_BAD_ACCESS

3 个答案: