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