如果目录不存在，是否有更安全的方法来创建目录？

I've found this way of creating a directory if it does not exist. But it looks a bit wonky and I am afraid that this can go wrong in 1 of 1000 attempts.

如果目录不存在，我发现了这种创建目录的方法。但它看起来有点不稳定，我担心这会在1000次尝试中出现错误。

if(![[NSFileManager defaultManager] fileExistsAtPath:bundlePath]) {
    [[NSFileManager defaultManager] createDirectoryAtPath:bundlePath withIntermediateDirectories:YES attributes:nil error:NULL];
}

There is only this awkward method fileExistsAtPath which also looks for files and not only directories. But for me, the dangerous thing is: What if this goes wrong? What shall I do? What is best practice to guarantee that the directory is created, and only created when it does not exist?

只有这个笨拙的方法fileExistsAtPath也可以查找文件，而不仅仅是目录。但对我来说，危险的是：如果这出错怎么办？我该怎么办？保证创建目录的最佳做法是什么，只有在目录不存在时才创建？

I know file system operations are never safe. Device could loose battery power suddenly just in the moment where it began shoveling the bits from A to B. Or it can stumble upon a bad bit and hang for a second. Maybe in some seldom cases it returns YES even if there is no directory. Simply put: I don't trust file system operations.

我知道文件系统操作永远不会安全。设备可能会在它开始从A到B的位置时突然耗尽电池电量。或者它会偶然发现一个坏位并挂了一秒钟。也许在一些很少的情况下，即使没有目录，它也会返回YES。简单地说：我不相信文件系统操作。

How can I make this absolutely safe?

我怎样才能绝对安全？

4 个解决方案

#1

You can actually skip the if, even though Apple's docs say that the directory must not exist, that is only true if you are passing withIntermediateDirectories:NO

你实际上可以跳过if，即使Apple的文档说该目录不能存在，只有在你传递中间目录时才会这样：

That puts it down to one call. The next step is to capture any errors:

这归结为一个电话。下一步是捕获任何错误：

NSError * error = nil;
[[NSFileManager defaultManager] createDirectoryAtPath:bundlePath
                          withIntermediateDirectories:YES
                                           attributes:nil
                                                error:&error];
if (error != nil) {
    NSLog(@"error creating directory: %@", error);
    //..
}

This will not result in an error if the directory already exists.

如果目录已存在，则不会导致错误。

#2

For Swift 3.0

对于Swift 3.0

do {
    try FileManager.default.createDirectory(atPath: folder, withIntermediateDirectories: true, attributes: nil)
} catch {
    print(error)
}

#3

NSFileManager *fileManager= [NSFileManager defaultManager]; 
if(![fileManager fileExistsAtPath:directory isDirectory:&isDir])
    if(![fileManager createDirectoryAtPath:directory withIntermediateDirectories:YES attributes:nil error:NULL])
        NSLog(@"Error: Create folder failed %@", directory);

From an SO topic here.

来自SO主题。

After creating a directory, you can flush the file system then check to see if your newly created directory exists. This is probably overkill, but you can never have too much overkill.

创建目录后，可以刷新文件系统，然后检查新创建的目录是否存在。这可能是矫枉过正，但你永远不会有太多的矫枉过正。

#4

In swift 2 it looks like this:

在swift 2中它看起来像这样：

do {
    try NSFileManager.defaultManager().createDirectoryAtPath(pathURL.absoluteString, withIntermediateDirectories: true, attributes: nil)
} catch {
    print(error)
}

#1