@interface NSFileManager : NSObject

@interface NSFileManager : NSObject

NSFileManager操作：

1.文件夹创建删除

2.文件创建删除

3.清除数据缓存

以上办法都在这里：https://developer.apple.com/library/mac/documentation/FileManagement/Conceptual/FileSystemProgrammingGuide/AccessingFilesandDirectories/AccessingFilesandDirectories.html#//apple_ref/doc/uid/TP40010672-CH3-SW1

笔记：

NSFileManager的文件对象操作的优势：

 NSFileManager. An advantage of file reference URLs is that they are less fragile than path-based URLs while your app is running. If the user moves a file in the Finder, any path-based URLs that refer to the file immediately become invalid and must be updated to the new path. However, as long as the file moved to another location on the same disk, its unique ID does not change and any file reference URLs remain valid.

1>sandbox中的执意要两大部分：bundle container and  data container ,etc.，如图：

2>主要记录Data container

2.1>Documents/ 可以创建保存文件和文件夹，目的很明确，让用户创建和操作的文件(暴漏的)。文件的内容可以在iTunces备份。

2.2>Library/ 跟Documents文件差不多，但是它里面在创建之初就已经创建几个默认的文件夹了，eg：Caches/  Preferences/ etc.(Preference/ 中放着NSUserDefault关联的plist文件)

Caches/ 中存在SnapShot：app截图 。

2.3>Library/Application support/ 文件，一般是用户区创建也可以操作，但是是hidden(不暴漏的)，用于存储配置文件，模板等app系统配置相关的文件。

3>Accessing Files and Directories(文件路径操作读写)

Before you can open a file, you first have to locate it in the file system. The system frameworks provide many routines for obtaining references to many well-known directories, such as the Library directory and its contents. You can also specify locations manually by building a URL or string-based path from known directory names.

When you know the location of a file, you can then start planning the best way to access it. Depending on the type of file, you may have several options. For known file types, you typically use built-in system routines to read or write the file contents and give you an object that you can use. For custom file types, you may need to read the raw file data yourself.

Choose the Right Way to Accessing Files

Although you can open any file and read its contents - lists the common file types supported by the system along with information about how you access them.

读到这里，大体上说拼接一个Location来获取文件，有两种方法：NSURL和NSString

但是，官方文档说了，如果你想获取一个本地的地址，最好使用NSURL来获取本地地址Access文件，文档中说啦：

The preferred way to specify the location of a file or directory is to use the NSURL class. Although the NSString class has many methods related to path creation, URLs offer a more robust(牛逼的) way to locate files and directories. For apps that also work with network resources, URLs also mean that you can use one type of object to manage items located on a local file system or on a network server

建议用NSURL拼接本地地址

当然，官方文档又说了，还有一个东西跟NSURL功能可以互换的，叫做CGURLRef

Note: In addition to NSURL, you can also use the CFURLRef opaque type to manipulate paths as URLs. The NSURL class is toll-free bridged with the CFURLRef type, which means you can use them interchangeably in your code. For more information about how to create and manipulate URLs using Core Foundation, see CFURL Reference.

CGURLRef官方也推荐

使用NSURL来创建文件夹：

    NSFileManager * shareFM = [NSFileManager defaultManager];
    NSArray * possibleURLs = [shareFM URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask];
    NSURL * appSupportDir = nil;
    NSURL * appDirectory = nil;

    )
    {
        appSupportDir = [possibleURLs objectAtIndex:];
    }
    if (appSupportDir)
    {
        NSString * appBundleID = [[NSBundle mainBundle] bundleIdentifier];
        appDirectory = [appSupportDir URLByAppendingPathComponent:appBundleID];
        [shareFM createDirectoryAtURL:appDirectory withIntermediateDirectories:YES attributes:nil error:nil];
    }

    NSLog(@"%@",appDirectory);

NSURL创建文件夹

4.Enumerating the Contents of a Directory // 遍历文件夹中文件

Enumerating a directory one file at a time is recommended when you want to search for a specific file and stop enumerating when you find it. File-by-file enumeration uses the NSDirectoryEnumerator class, which defines the methods for retrieving items. Because NSDirectoryEnumerator itself is an abstract class, however, you do not create instances of it directly. Instead, you use either the enumeratorAtURL:includingPropertiesForKeys:options:errorHandler: or the enumeratorAtPath: method of NSFileManager object to obtain a concrete instance of the class for use in your enumeration.

遍历文件

5.Use Secure Coding Practices（使用安全编码规范）

5.1>删除一个空文件的时候，要求之前判断文件是空的时候，在执行删除。

5.2>在进行文件操作的时候权限不是执行操作独立的，所以在你创建一个文件之前判断她是不存在的，或者你必须肯定读，写数据的文件是你创建的。

5.3>无论任何时候，操作文件使用名称好过文件路径，这样的方式可以保证你一直操作同一个文件。

5.4>把创建文件的方法独立成一个方法，这样你可以更好的知道你所创建的文件是不是已经一个已经存在的。

5.5>读一个文件的时候，首先判断是否有是自己权限和你要操作的权限，这样可以避免程序hanging，在失败的时候可以进行很好的失败处理。