NSSearchPathForDirectoriesInDomains解释混乱

我刚学习这段代码来检查文件是否存在：

NSString *path; NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); path = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"SomeDirectory"]; path = [path stringByAppendingPathComponent:@"SomeFileName"]; if ([[NSFileManager defaultManager] fileExistsAtPath:path]) { 

但我有点困惑。 通过以下行：

 NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES); 

确定我理解方法NSSearchPathForDirectoriesInDomains根据您传递给此方法的参数返回路径。 但是这个用户（编写代码的人）盲目地传递了全class！ （参考NSDocumentDirectory，NSUserDOmainMask）。 他唯一正确传递的是BOOL YES。 我检查了苹果文档，它说：

NSSearchPathForDirectoriesInDomains创建目录搜索路径列表。

 NSArray * NSSearchPathForDirectoriesInDomains ( NSSearchPathDirectory directory, NSSearchPathDomainMask domainMask, BOOL expandTilde ); 

我在苹果文档中搜索了NSSearchPathDirectory和NSSearchPathDomainMask，他们建议我必须传递一个数字

这表明需要将一个数字传递给方法？ 有人可以解释一下这条线吗？ 谢谢

Answer 1

阅读Foundation框架常量的文档：
http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Miscellaneous/Foundation_DataTypes/Reference/reference.html#//apple_ref/doc/c_ref/NSDocumentDirectory

这是正确的用法，因为那些不是类而是常量！

---

NSSearchPathDomainMask

搜索路径域常量，指定NSSearchPathDirectory类型的基本位置。

 enum { NSUserDomainMask = 1, //this one NSLocalDomainMask = 2, NSNetworkDomainMask = 4, NSSystemDomainMask = 8, NSAllDomainsMask = 0x0ffff, }; typedef NSUInteger NSSearchPathDomainMask; 

---

NSSearchPathDirectory

这些常量指定各种目录的位置。

 enum { NSApplicationDirectory = 1, NSDemoApplicationDirectory, NSDeveloperApplicationDirectory, NSAdminApplicationDirectory, NSLibraryDirectory, NSDeveloperDirectory, NSUserDirectory, NSDocumentationDirectory, NSDocumentDirectory, // this one NSCoreServiceDirectory, NSAutosavedInformationDirectory = 11, NSDesktopDirectory = 12, NSCachesDirectory = 13, NSApplicationSupportDirectory = 14, NSDownloadsDirectory = 15, NSInputMethodsDirectory = 16, NSMoviesDirectory = 17, NSMusicDirectory = 18, NSPicturesDirectory = 19, NSPrinterDescriptionDirectory = 20, NSSharedPublicDirectory = 21, NSPreferencePanesDirectory = 22, NSItemReplacementDirectory = 99, NSAllApplicationsDirectory = 100, NSAllLibrariesDirectory = 101 }; typedef NSUInteger NSSearchPathDirectory;