iphone - NSSearchPathForDirectoriesInDomains 解释混淆

Question

我刚刚研究了检查文件是否存在的代码:

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

但是我有点困惑。通过以下行:

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

好的，我知道 NSSearchPathForDirectoriesInDomains 方法会根据您传递给该方法的参数返回一个路径。但是这个用户(写代码的人)正在盲目地传递整个类! (引用NSDocumentDirectory、NSUserDOmainMask)。他唯一正确通过的是 BOOL YES。我查看了苹果文档，上面写着:

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

这表明需要将数字传递到方法中？有人可以解释一下那条线吗？谢谢

Answer 1

在此处阅读 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，因为它们不是类而是常量!

---

NSSearchPathDomainMask

Search path domain constants specifying base locations for the NSSearchPathDirectory type.

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

---

NSSearchPathDirectory

These constants specify the location of a variety of directories.

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;