对于NSFileManager的使用，一直以来我都是用[NSFileManager defaultManager]来获取单例的形式来进行相关操作。
NSFileManager *fileManager = [NSFileManager defaultManager];
if ([fileManager fileExistsAtPath:sourceFile]) {
NSError *error = nil;
if (![fileManager copyItemAtPath:sourceFile
toPath:destFile
error:&error]) {
// Deal with error
}
}引用Apple Developer在overview关于NSFileManager实例化的相关说明：
The methods of the shared NSFileManager object can be called from multiple threads safely. However, if you use a delegate to receive notifications about the status of move, copy, remove, and link operations, you should create a unique instance of the file manager object, assign your delegate to that object, and use that file manager to initiate your operations.
共享单例是可以在多线程下安全调用的。但是，如果你使用delegate来接受有关移动，复制，删除和链接操作的nitification时，应该创建一个唯一实例，将delegate和它绑定，并使用该实例来开始你的操作。
In iOS and Mac OS X v 10.5 and later you should consider using [[NSFileManager alloc] init] rather than the singleton method defaultManager. Instances ofNSFileManager are considered thread-safe when created using [[NSFileManager alloc] init].
所以，[NSFileManager defaultManager]获得的共享单例并不是线程安全的，官方推荐的做法时通过[[NSFileManager alloc]init]来实例化。
NSFileManager *fileManager = [[NSFileManager alloc] init];
if ([fileManager fileExistsAtPath:sourceFile]) {
NSError *error = nil;
if (![fileManager copyItemAtPath:sourceFile
toPath:destFile
error:&error]) {
// Deal with error
}
}
// [fileManager release]; //ARC不需要手动释放More:
- Apple Developer Docs：NSFileManager Class Reference
- Blog： NSFileManager defaultManager Is Not Thread Safe