ObjectiveC 文件操作二

10，文件委托，以便操作文件。头部看起来像是这样。

@interface MyFileManager : NSObject

@property(strong)NSFileManager *fileManager;

@end

.m文件

#import "MyFileManager.h"

@implementation MyFileManager

@synthesize fileManager;

@end

可以在头部引入接口。

#import <Foundation/Foundation.h>

@interface MyFileManager : NSObject<NSFileManagerDelegate>

@property(strong)NSFileManager *fileManager;

@end

MyFileManager里面的可选方法。是否能复制

- (BOOL)fileManager:(NSFileManager *)fileManager shouldCopyItemAtPath:(NSString *)srcPath  toPath:(NSString *)dstPath{

if([dstPath hasPrefix:@"/Users/Shared/Book/Protected"]){

NSLog(@"We cannot copy files into the protected folder and so this file was not copied");

return NO;

}

else{

NSLog(@"We just copied a file successfully");

return YES;

}

}

重写初始化方法

- (id)init {

self = [super init];

if (self) {

self.fileManager = [[NSFileManager alloc] init];

self.fileManager.delegate = self;

}

return self;

}

在main.m里面使用刚刚创建的类。

#import <Foundation/Foundation.h>

#import "MyFileManager.h"

int main (int argc, const char * argv[])

{

@autoreleasepool {

MyFileManager *myFileManager = [[MyFileManager alloc] init];

NSString *protectedDirectory = @"/Users/Shared/Book/Protected";

NSString *cacheDirectory = @"/Users/Shared/Book/Cache";

NSString *fileSource = @"/Users/Shared/Book/textfile.txt";

NSString *fileDestination1 = @"/Users/Shared/Book/Protected/textfile.txt";

NSString *fileDestination2 = @"/Users/Shared/Book/Cache/textfile.txt";

NSError *error = nil;

NSArray *listOfFiles;

NSLog(@"Look at directories BEFORE attempting to copy");

listOfFiles = [myFileManager.fileManager contentsOfDirectoryAtPath:protectedDirectory

error:&error];

NSLog(@"List of files in protected directory (before):%@", listOfFiles);

listOfFiles = [myFileManager.fileManager contentsOfDirectoryAtPath:cacheDirectory

error:&error];

NSLog(@"List of files in cache directory (before):%@", listOfFiles);

//Attempt to copy into protected folder:

BOOL fileCopied1 = [myFileManager.fileManager copyItemAtPath:fileSource

toPath:fileDestination1

error:&error];

if(error)

NSLog(@"There was an error, %@.  fileCopied1 = %i", error, fileCopied1);

//Attempt to copy into cache folder:

BOOL fileCopied2 =  [myFileManager.fileManager copyItemAtPath:fileSource

toPath:fileDestination2

error:&error];

if(error)

NSLog(@"There was an error, %@.  fileCopied2 = %i", error, fileCopied2);

NSLog(@"Look at directories AFTER attempting to copy");

listOfFiles = [myFileManager.fileManager contentsOfDirectoryAtPath:protectedDirectory

error:&error];

NSLog(@"List of files in protected directory (after):%@", listOfFiles);

listOfFiles = [myFileManager.fileManager contentsOfDirectoryAtPath:cacheDirectory

error:&error];

NSLog(@"List of files in cache directory (after):%@", listOfFiles);

}

return 0;

}

此例子简单说明了委托方法的应用。

11，

使用文件或其他来源的数据。

组合字符串并写入文件。

NSUInteger length = 3;

char bytes1[length];

bytes1[0] = 'A';

bytes1[1] = 'B';

bytes1[2] = 'C';

char bytes2[length];

bytes2[0] = 'D';

bytes2[1] = 'E';

bytes2[2] = 'F’;

声明可变数组。

NSMutableData *mutableData = [[NSMutableData alloc] init];

可变数组有很多方法，具体参考手册。

下面是代码。

NSUInteger length = 3;

char bytes1[length];

bytes1[0] = 'A';

bytes1[1] = 'B';

bytes1[2] = 'C';

for (int i=0;i<sizeof(bytes1);i++)

NSLog(@"bytes1[%i] = %c", i, bytes1[i]);

char bytes2[length];

bytes2[0] = 'D';

bytes2[1] = 'E';

bytes2[2] = 'F';

for (int i=0;i<sizeof(bytes2);i++)

NSLog(@"bytes2[%i] = %c", i, bytes2[i]);

NSMutableData *mutableData = [[NSMutableData alloc] init];

[mutableData appendBytes:bytes1

length:length];

[mutableData appendBytes:bytes2

length:length];

NSLog(@"mutableData = %@", mutableData);

char *bytesFromData = (char *)[mutableData bytes];

for (int i=0;i<length*2;i++)

NSLog(@"bytesFromData[%i] = %c", i, bytesFromData[i]);

NSError *error = nil;

BOOL dataSaved = [mutableData writeToFile:@"/Users/Shared/Book/datadump.txt"

options:NSDataWritingAtomic

error:&error];

if(dataSaved)

NSLog(@"mutableData successfully wrote contents to file system");

else

NSLog(@"mutableData was unsuccesful in writing out data because of %@", error);

12，NSCache缓存数据。

比如创建一个ViewController类。

.h文件里面

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController

@property (strong) NSCache *cache;

@property (assign) BOOL regularLogo;

@property (strong) UIImageView *myImageView;

@property (strong) UIButton *loadImageButton;

- (void)presentImage;

@end

.m文件里面

#import "ViewController.h"

@implementation ViewController

-(void)viewDidLoad{

[super viewDidLoad];

//set up the cache

self.cache = [[NSCache alloc] init];

} @end

只要试图被激活就可以使用缓存。

下面是具体代码。

Listing 4-14. AppDelegate.h #import <UIKit/UIKit.h>

@class ViewController;

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

@property (strong, nonatomic) ViewController *viewController;

@end

Listing 4-15. AppDelegate.m #import "AppDelegate.h"

#import "ViewController.h"

@implementation AppDelegate

@synthesize window = _window;

@synthesize viewController = _viewController;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

// Override point for customization after application launch.

self.viewController = [[ViewController alloc]

initWithNibName:@"ViewController" bundle:nil];

self.window.rootViewController = self.viewController;

[self.window makeKeyAndVisible];

return YES;

} @end

Listing 4-16. ViewController.h #import <UIKit/UIKit.h>

@interface ViewController : UIViewController

@property (strong) NSCache *cache;

@property (assign) BOOL regularLogo;

@property (strong) UIImageView *myImageView;

@property (strong) UIButton *loadImageButton;

- (void)presentImage;

@end

Listing 4-17. ViewController.m #import "ViewController.h"

@implementation ViewController

@synthesize cache, regularLogo, myImageView, loadImageButton;

-(void)viewDidLoad{

[super viewDidLoad];

//Change the view's background color to white

self.view.backgroundColor = [UIColor whiteColor];

//Load the regular logo first

self.regularLogo = YES;

//set up the cache

self.cache = [[NSCache alloc] init];

//Setup the button

self.loadImageButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];

self.loadImageButton.frame = CGRectMake(20, 415, 280, 37);

[self.loadImageButton addTarget:self

action:@selector(presentImage)

forControlEvents:UIControlEventTouchUpInside];

[loadImageButton setTitle:@"Present Image" forState:UIControlStateNormal];

[self.view addSubview:loadImageButton];

//Setup the UIImageView

self.myImageView = [[UIImageView alloc] init];

self.myImageView.frame = CGRectMake(0, 0, 320, 407);

self.myImageView.contentMode = UIViewContentModeScaleAspectFit;

[self.view addSubview:self.myImageView];

}

- (void)presentImage{

if(regularLogo){

NSString *key = @"regular-logo";

NSPurgeableData *data = [cache objectForKey:key];

if(!data){

NSString *bundlePath = [[NSBundle mainBundle] bundlePath];

NSString *imagePath = [NSString stringWithFormat: @"%@/MobileAppMastery-Log.png", bundlePath];

data = [NSPurgeableData dataWithContentsOfFile:imagePath];

[cache setObject:data forKey:key];

NSLog(@"Retrieved resource(%@) and added to cache", key);

} else

NSLog(@"Just retrieved resource(%@)", key);;

self.myImageView.image = [UIImage imageWithData:data];

regularLogo = NO;

} else{

NSString *key = @"greyscale-logo";

NSPurgeableData *data = [cache objectForKey:key];

if(!data){

NSString *bundlePath = [[NSBundle mainBundle] bundlePath];

NSString *imagePath = [NSString stringWithFormat:@"%@/MAM_Logo_Square_No_Words_Grayscale.png", bundlePath];

data = [NSPurgeableData dataWithContentsOfFile:imagePath];

[cache setObject:data forKey:key];

NSLog(@"Retrieved resource(%@) and added to cache", key);

} else

NSLog(@"Just retrieved resource(%@)", key);

self.myImageView.image = [UIImage imageWithData:data];

regularLogo = YES;

}

} @end