在应用程序中跨类共享方法的最佳实践是什么？

Question

我仍然在尝试在面向对象的世界中应该如何做事情，我想我的问题是我不知道如何最好地利用封装。具体地说，我在项目中的几个类中使用了大量的小代码。例如：

+ (NSString *)getFormattedDate;
+ (NSString *)getResultsFilePath;
+ (NSError *)removeFileFromCache:(NSString *)fileName;

这些都是我在多个类中使用的3-5行方法。我的标准做法是将这些代码片段放到一个Utility.inc文件中，并在需要时调用它们。这在面向对象的世界中合适吗?或者每个类都应该是自包含的？如果合适的话，你会把代码放到一个单例中，还是只放在一个常规的类文件中，并在你想要使用这些方法的每个类中放入[Utilities alloc init]？

Answer 1

谢谢你的回答。我不确定这是不是正确的方法，但这就是我在刚刚提交的项目中所做的。

我创建了两个类，一个用于Utility方法，另一个用于全局变量。Utilities类中的方法都是类方法，因为它们对文件和常量或全局变量进行操作。然后我为全局变量创建了一个单例。我的所有全局常量都在.pch文件中。另外，在.pch文件中，我放入了以下两行代码，以便实用程序和全局变量随处可用。

 // File for utilities like file delete, find Documents file
    #import "Utilities.h" 
    #import "Globals.h"

访问这些方法很简单。下面是调用这两种方法为电子邮件生成HTML标头的示例。

NSString *gameNameHeader = [NSString stringWithFormat:@"<p>&nbsp</p><h1>%@ Results</h1><h2>%@%@</h2>",GAME_NAME_TITLE,[Utilities formattedClientName], [Utilities formattedDate]];

如果任何人都可以使用它，这是我当前版本的代码。(抱歉的格式-我似乎不能让维基合作。)

@interface Utilities : NSObject {


}

+ (NSString *)formattedDate;
+ (NSString *)formattedClientName;

+ (NSString *)cachedResultsFilePath;
+ (NSString *)cachedResultsFileContents;
+ (NSString *)resultsFileName;
+ (NSError *)removeFileFromCache:(NSString *)fileName;

+ (NSString *)applicationCachesDirectory;
+ (NSString *)applicationDocumentsDirectory;
+ (NSString *)applicationLibraryDirectory;

+ (NSError *)copyCachedResultsToFile;
@end



    #import "Utilities.h"
@implementation Utilities {

    }

+ (NSString *)formattedDate {
    NSDateFormatter* dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd"];
    NSString *todaysDate = [dateFormatter stringFromDate:[NSDate date]];
    return todaysDate;
}

+ (NSString *)formattedClientName {
    NSString *client = [NSString stringWithFormat:@" "]; 
    if( [Globals sharedInstance].currentClient ) client = [NSString stringWithFormat:@" %@ ",[Globals sharedInstance].currentClient];
    return client;
}

+ (NSString *)cachedResultsFilePath {
    NSString *resultsFilePath = [[self applicationCachesDirectory] stringByAppendingPathComponent:@"Results.txt"];
    return resultsFilePath;
}

+ (NSString *)cachedResultsFileContents {
    NSStringEncoding encoding; NSError* error = nil;
    NSString *resultsText = [NSString stringWithContentsOfFile:[self cachedResultsFilePath] usedEncoding:&encoding error:&error];
    return resultsText;
}

+ (NSString *)resultsFileName {
    return [NSString stringWithFormat:@"%@ Results%@%@.html",GAME_NAME_TITLE,[self formattedClientName],[self formattedDate] ];

}

+ (NSError *)removeFileFromCache:(NSString *)fileName {
    NSError *error = nil;
    NSFileManager *localFileManager=[[NSFileManager alloc] init];
    NSString *fullPath = [NSString stringWithFormat:@"%@/%@", [self applicationCachesDirectory],fileName];
    [localFileManager removeItemAtPath: fullPath error:&error ];
    return error;
}

+ (NSString *)applicationCachesDirectory {
    return [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
}

+ (NSString *)applicationDocumentsDirectory {
    return [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
}

+ (NSString *)applicationLibraryDirectory {

    return [NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES) lastObject];
}

+ (NSError *)copyCachedResultsToFile {
    // Grab the header and footer and put it around the cached data
    NSStringEncoding encoding; NSError *error = nil;
    NSString *htmlHeaderTextPath = [[NSBundle mainBundle] pathForResource:@"HTML_header" ofType:@"html" ]; 
    NSString *htmlHeaderText = [NSString stringWithContentsOfFile:htmlHeaderTextPath usedEncoding:&encoding error:&error];

    NSString *cachedResultsText = [NSString stringWithContentsOfFile:[self cachedResultsFilePath] usedEncoding:&encoding error:&error];
    // Write the results to a file if there are any
    if (cachedResultsText) {
        NSString *htmlFooterTextPath = [[NSBundle mainBundle] pathForResource:@"HTML_footer" ofType:@"html" ]; 
        NSString *htmlFooterText = [NSString stringWithContentsOfFile:htmlFooterTextPath usedEncoding:&encoding error:&error];

        NSString *gameNameHeader = [NSString stringWithFormat:@"<h1>%@ Results for%@%@</h1>",GAME_NAME_TITLE,[self formattedClientName],[self formattedDate] ];
        NSString *tempStringP1 = [htmlHeaderText stringByAppendingString:gameNameHeader];
        NSString *tempStringP2 = [tempStringP1 stringByAppendingString:cachedResultsText];

        NSString *formattedTextForPrinting = [tempStringP2 stringByAppendingString:htmlFooterText];
        NSString *resultsFilePath = [ [Utilities applicationDocumentsDirectory] stringByAppendingPathComponent:[self resultsFileName] ];
        if ( !([[NSFileManager defaultManager] fileExistsAtPath:resultsFilePath]) ) {
            if (! ([[NSFileManager defaultManager] createFileAtPath:resultsFilePath contents:nil attributes:nil]) ) {
                NSLog(@"Error was code: %d - message: %s", errno, strerror(errno));
            }
        }
        NSFileHandle *fileHandler = [NSFileHandle fileHandleForUpdatingAtPath:resultsFilePath];
        [fileHandler writeData:[formattedTextForPrinting dataUsingEncoding:NSUTF8StringEncoding]];
        [fileHandler closeFile];

    }
     return error;
}
@end

单例中的全局变量。可能不是线程安全的，但我现在并不关心。

@interface Globals : NSObject {


}
@property (nonatomic, strong) NSString *currentClient;
@property (nonatomic, strong) NSString *showmePict;
@property BOOL checkBoxes;

+ (Globals *)sharedInstance;

- (void)resetClient;

@end

@实现全局变量{

}

static Globals *singleton = nil;
@synthesize currentClient = _currentClient;
@synthesize showmePict = _showmePict;
@synthesize checkBoxes = _checkBoxes;

+(Globals *) sharedInstance {

    NSLog (@"sharedInstance of Globals called.");

    if (nil != singleton) return singleton;
    static dispatch_once_t pred;        // lock
    dispatch_once(&pred, ^{             // this code is at most once
        singleton = [[Globals alloc] init];
    });

    return singleton;

}

- (void)resetClient {
    self.currentClient = nil;
}


@end

Answer 2

研究一下如何使用Categories。对于您给出的示例，这些都是与某个特定类的对象相关的方法，这些对象恰好在您自己的几个类中使用。类别将允许您将这些常用方法放在与公共因素相关联的位置。

Answer 3

创建一个utitity singelton，它将只创建一个类，然后被其他类使用。