[NSFileManager defaultmanager]是操作文件的单例，二次封装可方便使用:

YJFileTool.h

#import <Foundation/Foundation.h>

typedef enum {//文件存储位置
    YJFileTypeDocument,
    YJFileTypeCache,
    YJFileTypeLibrary,
    YJFileTypeTem
}YJFileType;

@interface YJFileTool : NSObject

/** 获取Document路径 */
+(NSString *)getDocumentPath;
/** 获取Cache路径 */
+(NSString *)getCachePath;
/** 获取Library路径 */
+(NSString *)getLibraryPath;
/** 获取Tem路径 */
+(NSString *)getTemPath;

/** 判断文件是否存在 */
+(BOOL)fileIsExists:(NSString *)path;

/**
 *  创建目录下文件
 *  一般来说，文件要么放在Document,要么放在Labrary下的Cache里面
 *  这里也是只提供这两种存放路径

 *  @param fileName 文件名
 *  @param Type     路径类型
 *  @param context  数据内容
 *
 *  @return 文件路径
 */
+(NSString *)createFileName:(NSString *)fileName type:(YJFileType)Type context:(NSData *)context;



/**
 写入文件

 @param filePath 文件路径
 @param textData 内容
 @return 是否成功
 */
+(BOOL)writeToFileName:(NSString *)filePath data:(NSData *)textData;

@end

YJFileTool.m

#import "YJFileTool.h"

@implementation YJFileTool

+(NSString *)getDocumentPath{
    return [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
}
+(NSString *)getCachePath{
    return [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
}
+(NSString *)getLibraryPath{
    return [NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES) lastObject];
}
+(NSString *)getTemPath{
    return NSTemporaryDirectory();
}

+(NSString *)getRootPath:(YJFileType)type{
    switch (type) {
        case YJFileTypeDocument:
            return [self getDocumentPath];
            break;
        case YJFileTypeCache:
            return [self getCachePath];
            break;
        case YJFileTypeLibrary:
            return [self getLibraryPath];
            break;
        case YJFileTypeTem:
            return [self getTemPath];
            break;
        default:
            break;
    }
    return nil;
}

+(BOOL)fileIsExists:(NSString *)path{
    if (!path || path.length == 0) {
        return NO;
    }
    return [[NSFileManager defaultManager] fileExistsAtPath:path];
}

+(NSString *)createFileName:(NSString *)fileName type:(YJFileType)Type context:(NSData *)context{
    if (!fileName || fileName.length == 0) {
        return nil;
    }
    NSString *rootPath = [[self getRootPath:Type] stringByAppendingString:fileName];
    if ([self fileIsExists:rootPath]) {
        if (![[NSFileManager defaultManager]removeItemAtPath:rootPath error:nil]) {
            return nil;
        }
    }
    if ([[NSFileManager defaultManager]createFileAtPath:rootPath contents:context attributes:nil]) {
        return rootPath;
    }
    return nil;
}

//追加写文件
+(BOOL)writeToFileName:(NSString *)filePath data:(NSData *)textData{
    if (![self fileIsExists:filePath]) {
        return NO;
    }
    if (textData.bytes>0) {
        NSFileHandle *fileHandle = [NSFileHandle fileHandleForWritingAtPath:filePath];
        [fileHandle seekToEndOfFile];
        [fileHandle writeData:textData];
        [fileHandle synchronizeFile];
        [fileHandle closeFile];
        return YES;
    }else{
        return NO;
    }
}


@end

更多操作，请参考：https://blog.csdn.net/feng2qing/article/details/54974200