iOS 文件读写 (一)

一、iOS中的沙盒机制

  • iOS应用程序只能对自己创建的文件系统读取文件,这个独立、封闭、安全的空间,叫做沙盒。它一般存放着程序包文件(可执行文件)、图片、音频、视频、plist文件、sqlite数据库以及其他文件。

  • 每个应用程序都有自己的独立的存储空间(沙盒)

  • 一般来说应用程序之间是不可以互相访问

模拟器沙盒的位置

/User/userName/Library/Application Support/iPhone Simulator

当我们创建应用程序时,在每个沙盒中含有三个文件,分别是Document、Library和temp。

  • Document:一般需要持久的数据都放在此目录中,可以在当中添加子文件夹,iTunes备份和恢复的时候,会包括此目录。

  • Library:设置程序的默认设置和其他状态信息

  • temp:创建临时文件的目录,当iOS设备重启时,文件会被自动清除

    获取沙盒目录

    • 获取程序的根目录(home)目录

    NSString *homePath = NSHomeDirectory()

    • 获取Document目录

    NSArray  *paths = NSSearchPathDorDirectoriesInDomains(NSDocumentDicrectory,, NSUserDomainMark, YES);                                                                           NSString *docPath = [paths lastObject];

    • 获取Library目录

    NSArray *paths = NSSearchPathForDirectoriseInDomains(NSLibraryDirectory, NSUserDomainMask, YES);                                                                                   NSString *docPath = [paths lastObject];   

    • 获取Library中的Cache

    NSArray *paths = NSSearchPathForDirectoriseInDomains(NSCachesDirectory, NSUserDomainMask, YES);                                                                                   NSString *docPath = [paths lastObject];

    • 获取temp路径

    NSString *temp = NSTemporaryDirectory( );


    二、NSString类路径的处理方法

    文件路径的处理

    NSString *path = @"/Uesrs/apple/testfile.txt"

    • 常用方法如下

    获得组成此路径的各个组成部分,结果:("/","User","apple","testfile.txt")

    - (NSArray *)pathComponents;

    提取路径的最后一个组成部分,结果:testfile.txt

    - (NSString *)lastPathComponent;

    删除路径的最后一个组成部分,结果:/Users/apple

    - (NSString *)stringByDeletingLastPathCpmponent;

    将path添加到先邮路径的末尾,结果:/Users/apple/testfile.txt/app.txt

    - (NSString *)stringByAppendingPathConmponent:(NSString *)str;

    去路径最后部分的扩展名,结果:text

    - (NSString *)pathExtension;

    删除路径最后部分的扩展名,结果:/Users/apple/testfile

    - (NSString *)stringByDeletingPathExtension;

    路径最后部分追加扩展名,结果:/User/apple/testfile.txt.jpg

    - (NSString *)stringByAppendingPathExtension:(NSString *)str;


    三、NSData

    • NSData是用来包装数据的

    • NSData存储的是二进制数据,屏蔽了数据之间的差异,文本、音频、图像等数据都可用NSData来存储

    NSData的用法

    1.NSString与NSData互相转换

    NSData-> NSString                                                                                     NSString *aString = [[NSString alloc] initWithData:adataencoding:NSUTF8StringEncoding];

    NSString->NSData                                                                                      NSString *aString = @"1234abcd";
    NSData *aData = [aString dataUsingEncoding: NSUTF8StringEncoding]; 

    将data类型的数据,转成UTF8的数据

    +(NSString *)dataToUTF8String:(NSData *)data
    {
    NSString *buf = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    return [buf autorelease];
    }

    将string转换为指定编码 
    +(NSString *)changeDataToEncodinString:(NSData *)data encodin:(NSStringEncoding )encodin{
        NSString *buf = [[[NSString alloc] initWithData:data encoding:encodin] autorelease];
        return buf;
    }

    2. NSData 与 UIImage
    NSData->UIImage
    UIImage *aimage = [UIImage imageWithData: imageData];
     

    //例:从本地文件沙盒中取图片并转换为NSData
    NSString *path = [[NSBundle mainBundle] bundlePath];
    NSString *name = [NSString stringWithFormat:@"ceshi.png"];
    NSString *finalPath = [path stringByAppendingPathComponent:name];
    NSData *imageData = [NSData dataWithContentsOfFile: finalPath];
    UIImage *aimage = [UIImage imageWithData: imageData];

    3.NSData与NSArray  NSDictionary

    +(NSString *)getLocalFilePath:(NSString *) fileName
    {
    return [NSString stringWithFormat:@"%@/%@%@", NSHomeDirectory(),@“Documents”,fileName];
    }

    包括将NSData写进Documents目录
    从Documents目录读取数据
    在进行网络数据通信的时候,经常会遇到NSData类型的数据。在该数据是dictionary结构的情况下,系统没有提供现成的转换成NSDictionary的方法,为此可以通过Category对NSDictionary进行扩展,以支持从NSData到NSDictionary的转换。声明和实现如下:

    + (NSDictionary *)dictionaryWithContentsOfData:(NSData *)data {     
        CFPropertyListRef list = CFPropertyListCreateFromXMLData(kCFAllocatorDefault, (CFDataRef)data, kCFPropertyListImmutable, NULL);
        if(list == nil) return nil; 
        if ([(id)list isKindOfClass:[NSDictionary class]]) { 
             return [(NSDictionary *)list autorelease]; 
            } 
        else { 
             CFRelease(list); 
             return nil; 
            } 
    }


    四、文件管理常用方法

    NSFileManager

    创建一个文件并写入数据                                                                                    - (BOOL)createFileAtPath:(NSString *)path contents:(NSData *)data attributes:(NSDictionary *)attr;

    从一个文件中读取数据                                                                                       - (NSData *)contentsAtPath:(NSString *)path;

    scrPath路径上的文件移动到dstPath路径上,注意这里的路径是文件路径而不是目录          - (BOOL)moveItemAtPath:(NSString *)srcPath toPath:(NSString *)dstPath error:(NSError **) error;

    scrPath路径上的文件复制到dstPath路径上                                                            - (BOOL)copyItemAtPath:(NSString *)scrPath toPath:(NSString *)dstPath error:(NSError **) error;

    比较两个文件的内容是否一样                                                                               - (BOOL)contentsEqualAtPath:(NSString *)path1 andPath:(NSString *)path2;

    文件时候存在                                                                                                  - (BOOL)fileExistsAtPath:(NSString *)path;

    移除文件                                                                                                        - (BOOL)removeItemAtPath:(NSString *)path error:(NSError **) error;


    创建文件管理

    NSFileManager *fileManager = [NSFileManager defaultManager];                          NSString *path = [NSHomeDirectory( )  stringByAppendingPathComponent:@"holyBible.txt"];                                                                                                     NSString *text = @"abcdefg"; 

    将字符串转成NSData类型                                                                                 NSData *data = [text dataUsingEncoding: NSUTF8StringEncoding]; 

    写入文件                                                                                                       BOOL success = [fileManager createFileAtPath:path contents:data attributes:nil];


    创建文件夹 

    NSString *filePath = [path stringByAppendingPathComponent:@"holyBible.txt"];     NSString *contect = @"abcdefg";                                                                     BOOL success = [fm createFileAtPath:filePath contents:[content dataUsingEncoding: NSUTF8StringEncoding] attributes:nil];


    NSFileManager-读取内容                                                                                 NSData *fileData = [fileManager contentsAtPath:filePath];                                   NSString *content = [[NSString alloc] initWithData:fileData dataUsingEncoding: NSUTF8StringEncoding];

    NSData-读取内容                                                                                          NSString *filePath = [path stringByAppendingPathComponent:@"holyBible.txt"];     NSData *data = [NSData dataWithContentOfFile:filePath];

    NSString-读取内容                                                                                         NSString *filePath = [path stringByAppendingPathComponent:@"holyBible.txt"];     NSString *content = [[NSString stringWithContentsOfFile:filePath encoding:NSUTF8StringEncoding error:nil];

    移动、复制文件                                                                                             

    移动文件(重命名)                                                                                         NSString *toPath = [NSHomeDirectory( ) stringByAppendingPathComponent:@"hellogod/New Testament.txt"];                                                                              [fm createDirectoryAtPath:[toPath stringByDeletingLastPathComponent] withIntermediateDirectories:YES attributes:nil error:nil];                                                   NSError *error;                                                                                             BOOL isSuccess = [fm moveItemAtPath:filePath toPath:toPath error:&error];

    复制文件(重命名)                                                                                         NSString *copyPath = [NSHomeDirectory( ) stringByAppendingPathComponent:@"备份/Old Testament.txt"];                                                                                  [fm createDirectoryAtPath:[toPath stringByDeletingLastPathComponent] withIntermediateDirectories:YES attributes:nil error:nil];                                                   BOOL success = [fm copyItemAtPath:toPath toPath:toPath error:nil];

    删除文件、获取文件大小

    判断文件是否存在和删除文件                                                                               if([fm fileExistsAtPath])                                                                                     {                                                                                                                    if ([fm removeItemAtPath:copyPath])                                                                {                                                                                                                   NSLog(@"remove success");                                                                            }                                                                                                                  }

    获取文件大小                                                                                                  NSFileManager *fileManager = [NSFileManager defaultManager];                         获得文件的属性字典                                                                                         NSDictionary *attrDic = [fileManager attributesOfItemAtpath:sourcePath error:nil];  NSNumber *fileSize = [attrDic objectForKey:NSFileSize];   

    获取目录文件信息                                                                                            NSFileManager *fileManager = [NSFileManager defaultManager];                         NSString *enuPath = [NSHomeDirectoty( ) stringByAppendingPathComponent:@"Test"];                                                                                                           NSDictionaryEnumerator *dirEnum = [fileManager enumeratorAtPath:enuPath];     NSString *path = nil;                                                                                      while ((path = [dirEnum nextObject]} != nil)                                                        {                                                                                                                  NSLog(@"%@",path);                                                                                        }


    五、Plist文件

    String方式添加              

    NSString *path = [NSHomeDirectory( )  stringByAppendingPathComponent:@"Array.plist"];                    

    NSString *content = @"abcd";            

    [contect writeToFile:path atomically:YES encoding:NSUTF8StringEncoding error:nil];

    Array方式添加        

    NSString *path = [NSHomeDirectory( )  stringByAppendingPathComponent:@"Array.plist"];     

    [NSArray *array = [[NSArray alloc] initWithObjects:@"123", @"798",@"000",nil];       [array writeToFile:path atomically:YES];

    Dictionary方式添加          

    NSString *path = [NSHomeDirectory( )  stringByAppendingPathComponent:@"Dic.plist"];                        

    NSDictionary *dic = [NSDictionary alloc] initWithObjects:@"first",@"second",@"third"forKeys:@"123",@"456",@"798"];                                                                       [dic writeToFile:path atomically:YES];

    • 数组、字典只能将BOOL、NSNumber、NSString、NSData、NSDate、NSArray、NSDictionary写入属性列表plist文件

    六、读取文件类和常用方法

    • NSFileHandle类主要对文件内容进行读取和写入操作

    • NSFileManager类主要对文件的操作(删除、修改、移动、复制等等)

    常用处理方法

    + (id)fileHandleForReadingAtPath:(NSString *)path  打开一个文件准备读取     

    + (id)fileHandleForWritingAtPath:(NSString *)path  打开一个文件准备写入   

    + (id)fileHandleForUpdatingAtPath:(NSString *)path  打开一个文件准备更新  

    -  (NSData *)availableData; 从设备或通道返回可用的数据            

    -  (NSData *)readDataToEndOfFile; 从当前的节点读取到文件的末尾               

    -  (NSData *)readDataOfLength:(NSUInteger)length; 从当前节点开始读取指定的长度数据                           

    -  (void)writeData:(NSData *)data; 写入数据         

    -  (unsigned long long)offsetInFile;  获取当前文件的偏移量            

    -  (void)seekToFileOffset:(unsigned long long)offset; 跳到指定文件的偏移量     

    -  (unsigned long long)seekToEndOfFile; 跳到文件末尾        

    -  (void)truncateFileAtOffset:(unsigned long long)offset; 将文件的长度设为offset字节

    -  (void)closeFile;  关闭文件

    向文件追加数据

    NSString *homePath  = NSHomeDirectory( );        

    NSString *sourcePath = [homePath stringByAppendingPathConmpone:@"testfile.text"];                                            

    NSFileHandle *fielHandle = [NSFileHandle fileHandleForUpdatingAtPath:sourcePath];                                                        

    [fileHandle seekToEndOfFile];  将节点跳到文件的末尾          

    NSString *str = @"追加的数据"                   

    NSData* stringData  = [str dataUsingEncoding:NSUTF8StringEncoding];          

    [fileHandle writeData:stringData]; 追加写入数据       

    [fileHandle closeFile];

    定位数据                    

    NSFileManager *fm = [NSFileManager defaultManager];              

    NSString *content = @"abcdef";                      

    [fm createFileAtPath:path contents:[content dataUsingEncoding:NSUTF8StringEncoding] attributes:nil];                                                   

    NSFileHandle *fileHandle = [NSFileHandle fileHandleForReadingAtPath:path];      

    NSUInteger length = [fileHandle availabelData] length]; 获取数据长度       

    [fileHandle seekToFileOffset;length/2]; 偏移量文件的一半           

    NSData *data = [fileHandle readDataToEndOfFile];      

    [fileHandle closeFile];

    复制文件                           

    NSFileHandle *infile, *outfile; 输入文件、输出文件          

    NSData *buffer; 读取的缓冲数据                    

    NSFileManager *fileManager = [NSFileManager defaultManager];   

    NSString *homePath = NSHomeDirectory( );              

    NSString *sourcePath = [homePath stringByAppendingPathComponent:@"testfile.txt"];  源文件路径                                          

    NSString *outPath = [homePath stringByAppendingPathComponent:@"outfile.txt"]; 输出文件路径                               

    BOOL sucess  = [fileManager createFileAtPath:outPath contents:nil attributes:nil];  

    if (!success)          

    {                                                      

    return N0;                                                                                                   

    }                 

    infile = [NSFileHandle fileHandleForReadingAtPath:sourcePath]; 创建读取源路径文件

    if (infile == nil)                          

    {                                          

    return NO;                      

    }                           


    outfile = [NSFileHandle fileHandleForReadingAtPath:outPath]; 创建病打开要输出的文件                                                                                                                

    if (outfile == nil)                            

    {                                                               

    return NO;                                                    

    }                                             

    [outfile truncateFileAtOffset:0]; 将输出文件的长度设为0         

    buffer = [infile readDataToEndOfFile];  读取数据           

    [outfile writeData:buffer];  写入输入                        

    [infile closeFile];        关闭写入、输入文件               

    [outfile closeFile];






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