5 Useful

Objective-c

tips & patterns

By @ErikRalston

#1: Singleton

A design pattern where a class can have only one instance

Gist example of a Singleton Implementation

@interface Singleton : NSObject
 
+ (Singleton*)shared;
 
@end

Singleton implementation

@implementation Settings

+ (Singleton *)shared
{
    static Singleton *instance = nil;
    if(!instance)
        instance = [[super allocWithZone:nil] init];
    return instance;
}

+ (id)allocWithZone:(NSZone *)zone
{
    return [self shared];
}
 
@end

#2: Typedef your blocks!

A block of code bound to a variable

The syntax for declaration and usage is very hairy:

// Declaring block inline, every time@property (nonatomic,assign) (void (^)(void)) voidBlockProperty;
// Declaring a block once
typedef void (^VoidBlock)();

// Clean declarations forevermore
@property (nonatomic,assign) VoidBlock voidBlockProperty;

put them in a header file!

Gist example of a Blocks.h file

Be sure to include #ifndef!

#ifndef Blocks_h
#define Blocks_h
 
#import <Foundation/Foundation.h>
 
typedef void (^VoidBlock)();
 
typedef BOOL (^ReturnBoolBlock)();
 
typedef void (^DictionaryBlock)(NSDictionary *dictionary);
 
typedef void (^TableCellIndexPathBlock)(UITableViewCell *cell,NSIndexPath *indexPath);
 
#endif

#3: Operation queues

Queues of tasks, consumed by a particular thread

A lot of components in your app, including UIViews and instances of NSManagedObjectContext, should only be accessed by the thread that created them

Operation Queues to work asynchronously, but keep important work on the main thread

Simple Operation Handling

NSOperationQueue* otherQueue = [[NSOperationQueue alloc] init];
 
[queue addOperationWithBlock:^{
    
    // Do work off the main thread here
}];
 
NSOperationQueue* queue = [NSOperationQueue mainQueue];
 
[queue addOperationWithBlock:^{
    
    // Do work back on the main thread here
    
}];

Complex operation handling

Example complete gist of nested queuing

#4: Caching data in the sandbox

Good for storing bulky files that don't belong in CoreData

Gist of example file cache class

+(NSString *)cachesDirectoryName
{
    static NSString *cachePath = nil;
    if(!cachePath) {
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
        cachePath = [paths objectAtIndex:0];
    }
    
    return cachePath;
}

saving to the cache

+(NSString *)pathForName:(NSString *)name
{
    NSString *cachePath = [SimpleFilesCache cachesDirectoryName];

    NSString *path = [cachePath stringByAppendingPathComponent:name];

    return path;
}

+(void)saveToCacheDirectory:(NSData *)data withName:(NSString *)name
{
    NSString *path = [SimpleFilesCache pathForName:name];

    [data writeToFile:path atomically:YES];
}

Reading the cache

+(NSData *)cachedDataWithName:(NSString *)name
{
    NSString *path = [SimpleFilesCache pathForName:name];

    BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:path];

    if(fileExists) {
        
        NSData *data = [NSData dataWithContentsOfFile:path];

        return data;
        
    } else {
        return nil;
    }
}

#5: automatic documentation

Appledoc offers automated generation of documentation

(Like Doxygen, Sandcastle, etc)

All you need to do is format your comments correctly on protocols, classes, and methods

Installing is easy using brew!

 brew install appledoc

running appledoc

Always run from the project code directory

(Do not try to document your Cocoapods)

Command-line documentation generator

  appledocs      --project-name Flex      --project-company Flex      --output ../appledocs/      .

appledocs results

Default behavior is to install into XCode Documentation System

Possible to get same docs as HTML

appledocs result

Integrated docs with the IDE