objective-c 使用文件

 Foundation 框架请允许你利用文件系统对文件或目录执行基本操作。这些基本操作是由NSFileManager类提供的，

这个类的方法具有如下功能：

• 创建 一个新文件
• 从现有文件中读取数据
• 将数据写入文件中
• 重新命名文件
• 删除文件
• 测试文件是否存在
• 确定文件的大小及其他属性
• 复制文件
• 测试两个文件的内容是否相同

上述多数据操作也可以直接对目录进行。例如，可以创建目录，读取其中的内容，或者删除目录。

 

管理文件和目录

每个文件方法都是对NSFileManager对象的调用，而NSFileManager对象 是通过向类发送一条defaultManager消息创建的，

如下所示：

 

NSFileManager *fm

 ...

fm = [NSFileManager defaultManager];

 

例如,要从当前目录删除名为todolist的文件，首先要创建一个NSFileManager对象(如前面所示)，然后调用removeFileAtPath方法，

代码如下：

[fm removeFileAtPath: @"todolist" handler:nil];

可以测试返回结果，以确保文件删除：

if([fm removeFileAtPath:@"todolist" handler:nil] == NO)

{

    NSLog(@"Couldn't remove file todolist");

    return 1;

}

 

下面是一个基本文件操作的例子：

//Basic ifle operations
//Assumes the existence of a file called "testfile"
//in ther current working directory
#import <Foundation/NSObject.h>
#import <Foundation/NSString.h>
#import <Foundation/NSFileManager.h>
#import <Foundation/NSAutoreleasePool.h>
#import <Foundation/NSDictionary.h>

int main(int argc, const char *argv[])
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSString *fName = @"testfile.txt";
    NSFileManager *fm;
    NSDictionary *attr;

    //Need to create an instance of the file manager
    fm = [NSFileManager defaultManager];

    //Let's make sure our test file exists first
    if([fm fileExistsAtPath: fName] == NO)
    {
        NSLog(@"File doesn't exist'");
        return 1;
    }

    //Now let's make a copy

    if([fm copyPath: fName toPath: @"newfile.txt" handler:nil] == NO)
    {
        NSLog(@"File copy failed");
        return 2;
    }

    //Let's test to see if the two files are identical
    if([fm contentsEqualAtPath: fName andPath: @"newfile.txt"] == NO)
    {
        NSLog(@"Files are not equal!");
        return 3;
    }

    //Now let's rename the copy

    if([fm movePath: @"newfile.txt" toPath: @"newfile2.txt" handler:nil] == NO)
    {
        NSLog(@"File rename failed!");
        return 4;
    }

    //Get the size of newfile2

    if((attr = [fm fileAttributesAtPath: @"newfile2.txt" traverseLink:NO]) == nil)
    {
        NSLog(@"Couldn't get file attributes!");
        return 5;
    }

    NSLog(@"File size is %i bytes",[[attr objectForKey: NSFileSize] intValue]);

    //And finally, let's delete the original file
    if([fm removeFileAtPath: fName handler:nil] == NO)
    {
        NSLog(@"File removal failed!");
        return 6;
    }

    NSLog(@"All operations were successful!");

    //Display the contents of the newly-created file

    NSLog(@"%@",[NSString stringWithContentsOfFile:@"newfile2.txt" encoding:NSUTF8StringEncoding error:nil]);

    [pool drain];
    return 0;
}

 

 

 

使用NSData类

 

使用文件时，需要频繁地将数据读入一个临时存储区，它通常称为缓冲区。当收集数据，以便随后将这些数据输出到文件中时，

通常也使用存储区。Foundation的NSData类提供了一种简单的方式，它用来设置缓冲 区、将文件的内容读入缓冲区，或将

缓冲区的内容写到一个文件。

 

下面是一个使用NSData 的例子：

 

#import <Foundation/NSObject.h>
#import <Foundation/NSString.h>
#import <Foundation/NSFileManager.h>
#import <Foundation/NSAutoreleasePool.h>
#import <Foundation/NSData.h>

//make a copy of file
int main(int argc, const char *argv[])
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSFileManager *fm;
    NSData *fileData;


    fm = [NSFileManager defaultManager];

    //Read the file newfile2
    fileData = [fm contentsAtPath: @"newfile2.txt"];

    if(fileData == nil)
    {
        NSLog(@"File read failed!");
        return 1;
    }

    //Write the data to newfile3
    if([fm createFileAtPath: @"newfile3.txt" contents: fileData attributes:nil] == NO)
    {
        NSLog(@"Couldn't create the copy!");
        return 2;
    }

    NSLog(@"File copy was successful!");

    [pool drain];
    return 0;
}

 

 

 

使用目录

 

NSFileManager类中，还有很多操作目录的方法。

下面是一个例子：

#import <Foundation/NSObject.h>
#import <Foundation/NSString.h>
#import <Foundation/NSFileManager.h>
#import <Foundation/NSAutoreleasePool.h>


int main(int argc, const char *argv[])
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSFileManager *fm;
    NSString *dirName = @"testdir";
    NSString *path;


    fm = [NSFileManager defaultManager];

    //Get current directory
    path = [fm currentDirectoryPath];
    NSLog(@"Current directory path is %@",path);

    //Create a new directory
    if([fm createDirectoryAtPath: dirName attributes: nil] == NO)
    {
        NSLog(@"Couldn't create directory!");
        return 1;
    }

    //Rename the new directory
    if([fm movePath: dirName toPath: @"newdir" handler: nil] == NO)
    {
        NSLog(@"Directory rename failed!");
        return 2;
    }

    //Change directory into the new directory
    if([fm changeCurrentDirectoryPath: @"newdir"] == NO)
    {
        NSLog(@"Change directory failed!");
        return 3;
    }

    //Now get and display current working directory
    path = [fm currentDirectoryPath];
    NSLog(@"Current directory path is %@ ",path);

    NSLog(@"All operations were successful!");


    [pool drain];
    return 0;
}

 

 

 

 

枚举目录中的内容

 

 

   有时需要枚举目录是的内容，就需要用到enumeratorAtPath:方法或者directoryContentsAtPath: 方法，来完成枚举过程。

如果使用第一种方法，一次可以枚举指定目录中的每个文件，默认情况下，如果其中一个文件为目录，那么也会递归枚举它的内容。

在这个过程中，通过向枚举对象发送一条skipDescendants消息，可以动态的地阻止递归过程，从而不再枚举目录中的内容。

   对于directoryContentsAtPath:方法，使用这个方法，可心枚举指定目录的内容，并在一个数组中返回文件列表。

如果这个目录中的任何文件本身是个目录，这个方法并不递归枚举它的内容。

 

下面一个例子是这两个方法的使用：

#import <Foundation/NSArray.h>
#import <Foundation/NSString.h>
#import <Foundation/NSFileManager.h>
#import <Foundation/NSAutoreleasePool.h>

//enumeratorAtPath:方法和directoryContentsAtPath:方法
//的区别是：前者遍历子目录，后者不遍历子目录
int main(int argc, const char *argv[])
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSFileManager *fm;
    NSString *path;
    NSDirectoryEnumerator *dirEnum;
    NSArray *dirArray;


    fm = [NSFileManager defaultManager];

    //Get current directory path
    path = [fm currentDirectoryPath];

    //Enumerate the directory

    dirEnum = [fm enumeratorAtPath:path];

    NSLog(@"Contents of %@: ",path);
    while((path = [dirEnum nextObject]) != nil)
    NSLog(@"%@",path);

    //Another way to enumerate a directory
    dirArray = [fm directoryContentsAtPath:[fm currentDirectoryPath]];
    NSLog(@"Contents using directoryContentsAtPath:");

    for(int i = 0; i < [dirArray count];i++)
    {
        NSLog(@"%@",[dirArray objectAtIndex: i]);
    }

    [pool drain];
    return 0;
}

 

使用路径:NSPathUtilities.h

 

NSPathUtilities.h包含了NSString的函数和分类扩展，它允许你操作路径名。

 

下面是一个例子：

#import <Foundation/NSArray.h>
#import <Foundation/NSString.h>
#import <Foundation/NSFileManager.h>
#import <Foundation/NSAutoreleasePool.h>
#import <Foundation/NSPathUtilities.h>


int main(int argc, const char *argv[])
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSFileManager *fm;
    NSString *fName = @"path.m";
    NSString *path,*tempdir,*extension,*homedir,*fullpath;
    NSString *upath = @"~stevekochan/progs/../ch16/./path.m";
    NSArray *components;


    fm = [NSFileManager defaultManager];

    //Get the temporary working directory

    tempdir = NSTemporaryDirectory();
    NSLog(@"Temporary Directory is %@",tempdir);

    //Extract the base directory from current directory
    path  = [fm currentDirectoryPath];
    NSLog(@"Base dir is %@",[path lastPathComponent]);

    //Create a full path to the file fName in current directory
    fullpath = [path stringByAppendingPathComponent:fName];
    NSLog(@"fullpath to %@ is %@",fName,fullpath);

    //Get the file name extension
    extension = [fullpath pathExtension];
    NSLog(@"extension for %@ is %@", fullpath,extension);

    //Get user's home directory
    homedir = NSHomeDirectory();
    NSLog(@"Your home directory is %@",homedir);

    //Divide a path into its components
    components = [homedir pathComponents];

    for(int i = 0; i < [components count]; i++)
    {
        NSLog(@"%@",[components objectAtIndex: i]);
    }

    //"Standardize" a path
    NSLog(@"%@ => %@",upath,[upath stringByStandardizingPath]);

    [pool drain];
    return 0;
}

 

 

 

 

复制文件和使用NSProcessInfo类

 

使用例子：

#import <Foundation/NSArray.h>
#import <Foundation/NSString.h>
#import <Foundation/NSFileManager.h>
#import <Foundation/NSAutoreleasePool.h>
#import <Foundation/NSPathUtilities.h>
#import <Foundation/NSProcessInfo.h>

//Implement a basic copy utility
int main(int argc, const char *argv[])
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSFileManager *fm;
    NSString *source,*dest;
    BOOL isDir;
    NSProcessInfo *proc = [NSProcessInfo processInfo];
    NSArray *args = [proc arguments];

    fm = [NSFileManager defaultManager];

    //Check for two arguments on the command line
    if([args count] != 3)
    {
        NSLog(@"Usage: %@ src dest ",[proc processName]);
        return 1;
    }

    source = [args objectAtIndex:1];
    dest = [args objectAtIndex:2];

    //Make sure the source file can be read
    if([fm isReadableFileAtPath: source] == NO)
    {
        NSLog(@"Can't read %@",source);
        return 2;
    }

    //See if the destination file is a directory
    //if it is , add the source to the end of the destination

    [fm fileExistsAtPath: dest isDirectory: &isDir];

    if(isDir == YES)
    {
        dest = [dest stringByAppendingPathComponent:[source lastPathComponent]];
    }

    //Remove the destination file if it already exists
    [fm removeFileAtPath:dest handler:nil];

    //Okay,time to perform the copy
    if([fm copyPath: source toPath: dest handler:nil] == NO)
    {
        NSLog(@"Copy failed");
        return 3;
    }

    NSLog(@"Copy of %@ to %@ succeeded!",source,dest);

    [pool drain];
    return 0;
}

 

 

 

 

基本文件操作:NSFileHandle

 

利用NSFileHandle类提供的方法，请允许我更有效地使用文件。一般而言，我们处理文件时都要经历以下三个步骤：

1.打开文件，并获取一个NSFileHandle对象，以便在后面的I/O操作中引用该文件。

2.对打开的文件执行I/O操作。

3.关闭文件。

 

下面的实例打开开始创建的原始testfile文件，读取它的内容，并将其复制到名为testout的文件中。

代码如下：

#import <Foundation/NSObject.h>
#import <Foundation/NSString.h>
#import <Foundation/NSFileManager.h>
#import <Foundation/NSFileHandle.h>
#import <Foundation/NSAutoreleasePool.h>
#import <Foundation/NSData.h>

//Implement a basic copy utility
int main(int argc, const char *argv[])
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSFileHandle *inFile,*outFile;
    NSData *buffer;

    //Open the file testfile.txt for reading
    inFile = [NSFileHandle fileHandleForReadingAtPath: @"testfile.txt"];
    if(inFile == nil)
    {
        NSLog(@"Open of testfile for reading failed");
        return 1;
    }

    //Create output file first if necessary
    [[NSFileManager defaultManager] createFileAtPath: @"testout.txt" contents:nil attributes:nil];

    //Now open outfile for writing
    outFile = [NSFileHandle fileHandleForWritingAtPath: @"testout.txt"];

    if(outFile == nil)
    {
        NSLog(@"Open of testout for writing failed");
        return 2;
    }

    //Truncate the output file since it may contain data
    [outFile truncateFileAtOffset:0];

    //Read the data from inFile and write it to outFile
    buffer = [inFile readDataToEndOfFile];

    [outFile writeData:buffer];

    //Close the two files
    [inFile closeFile];
    [outFile closeFile];

    //Verify the file's contents
    NSLog(@"%@",[NSString stringWithContentsOfFile:@"testout.txt"
          encoding: NSUTF8StringEncoding error:nil]);

    [pool drain];
    return 0;