COCOA-TIPS

UIView

Get subview by tag

UIView *subview = [[UIView alloc] init];
subview.tag = 1;
[self addSubview:subview];
[self viewWithTag:1]; // return subview

UIColor

Tile image to background

it's a bit weird this method belongs to UIColor not UIImage

UIImage *backgroundPattern = [UIImage imageNamed:@"backgroundPattern.png"];
view.backgroundColor = [UIColor colorWithPatternImage:backgroundPattern];

UIButton

Padding a UIButton's title via

button1.titleEdgeInsets = UIEdgeInsetsMake(0, 5, 0, 5);

increase tapable area of UIButton

UIImage *image = [UIImage imageNamed:@"button.png"];
UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
[button setImage:backImage forState:UIControlStateNormal];
[button addTarget:self.delegate action:@selector(buttonTapped) forControlEvents:UIControlEventTouchUpInside];
// u can set tapable area here, it won't strench image
backButton.frame = CGRectMake(8, 5, image.size.width + 10, image.size.height + 10);

UIImage

Generate animated images like GIF

UIImage *section1 = [UIImage imageNamed:@"image1.png"];
UIImage *section2 = [UIImage imageNamed:@"image2.png"];
UIImage *animatedImage = [UIImage animatedImageWithImages:@{section1, section2} duration:0.2];

// u can use `[UIImage animatedImageNamed:(NSString *)name duration:(NSTimeInterval)duration]` as well

Generate `UIImage` by url via

UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:MyURL]]];

Get first image from animated image

Suppose u use SDWebImage to download a bunch of GIFs, and put them to a scrollView, the app will become very slow, so it's better to just show first image as a preview.

// first u should check `animatedImage.images.count`
UIImage *firstImage = animatedImage.images[0];

Merging two images of different size via

UIImage *bottomImage = [UIImage imageNamed:@"bottom.png"]; //background image
UIImage *image       = [UIImage imageNamed:@"top.png"]; //foreground image

CGSize newSize = CGSizeMake(width, height);
UIGraphicsBeginImageContext( newSize );

// Use existing opacity as is
[bottomImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];

// Apply supplied opacity if applicable
[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height) blendMode:kCGBlendModeNormal alpha:0.8];

UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

UITableView

Disable selection highlighting

cell.selectionStyle = UITableViewCellSelectionStyleNone;

Set Selected row's text color via

cell.textLabel.highlightedTextColor = [UIColor redColor];

UILabel

sizeToFit will shrink label's additional area, set numberOfLines to 0 means unlimited number of lines(multiple line). via

NSArray

Filter array

NSArray *arr = @[@"hello", @"world", @"foo", @"bar"];
NSIndexSet *indexSet = [arr indexesOfObjectsPassingTest:^BOOL(id obj, NSUInteger idx, BOOL *stop){
	if ([obj rangeOfString:@"o"].location != NSNotFound) {
		return YES;
	}
	return NO;
}];
NSArray *filteredArr = [arr objectsAtIndexes:indexSet];
NSLog(@"filteredArr:%@", filteredArr);

Sort array via

NSArray *sortedArray;
sortedArray = [drinkDetails sortedArrayUsingComparator:^NSComparisonResult(id a, id b) {
    NSDate *first = [(Person*)a birthDate];
    NSDate *second = [(Person*)b birthDate];
    return [first compare:second];
}];

NSString

UIKit add some methods to NSString to make it easier to process certain tasks.

Calculate string's size

NSString *title = @"Foobar";
CGSize titleSize = [title sizeWithFont:[UIFont systemFontOfSize:14]];

Draw string

to reduce UIView's hierarchy, sometimes its convenience to draw all the content in drawRect method

NSString *title = @"Foobar";
CGPoint startPoint = CGPointMake(10, 10);
UIFont *font = [UIFont systemFontOfSize:14];

// draw the string in a single line
[title drawAtPoint:startPoint withFont:font];

// draw the string in a given area
CGRect rect = CGRectMake(0, 0, 150, 30);
[title drawInRect:rect withFont:font];

Check if contains certain substring

NSString *string = @"Hello World!";
NSLog(@"contains 'll'?: %i", [string rangeOfString:@"ll"].location != NSNotFound);

Trim string

NSString *string = @" this text has spaces before and after ";
NSString *trimmedString = [string stringByTrimmingCharactersInSet:
                                  [NSCharacterSet whitespaceCharacterSet]];

Replace string

NSString * myString = @"Hello,";
NSString * newString = [myString stringByReplacingOccurrencesOfString:@"," withString:@""];
NSLog(@"%@xx",newString);

NSData

Encode a string to NSData and Decode back via

NSString *originStr = @"teststring";
NSData *data = [originStr dataUsingEncoding:NSUTF8StringEncoding];
NSString *str = [NSString stringWithUTF8String:[data bytes]];

Convert UIImage to NSData

UIImage *image = [UIImage imageNamed:@"image.jpg"];
NSData *data = UIImageJPEGRepresentation(image, 1.0);
// if u want to convert to png
NSData *data = UIImagePNGRepresentation(image);

NSDate

Convert timestamp to NSDate

[NSDate dateWithTimeIntervalSince1970:timeStamp];

// convert NSDate to timestamp
- (NSTimeInterval)timeIntervalSince1970

Grand Central Dispatch (GCD)

Perform a block after duration

// Xcode has builtin snippets for this `dispatch_after` 
double delayInSeconds = 2.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
	// do some stuff
});

Key Value Coding (KVC)

KVC can automatically convert `NSNumber` to primitive value like `NSInteger`

#import <Foundation/Foundation.h>
@interface People : NSObject
@property (nonatomic, assign) NSInteger age;
@end

@implementation People @end

People *people = [[People alloc] init];
[people setValue:@(18) forKey:@"age"];
NSLog(@"people.age:%i", people.age);

Miscellaneous

use `DLog` instead of `NSLog`

when not in debug mode, it won't print anything.

#ifdef DEBUG
#   define DLog(fmt, ...) NSLog((@"%s [Line %d] " fmt), __PRETTY_FUNCTION__, __LINE__, ##__VA_ARGS__)
#else
#   define DLog(...)
#endif
 
// ALog always displays output regardless of the DEBUG setting
#define ALog(fmt, ...) NSLog((@"%s [Line %d] " fmt), __PRETTY_FUNCTION__, __LINE__, ##__VA_ARGS__)

Invoke a method of the receiver even it is private.

// this method has no return value!
[self performSelector:@selector(privateMethod) withObject:someObject];

Use @property in category with `objc_setAssociatedObject` and `objc_getAssociatedObject`

#import <objc/runtime.h>

static char  ObjectTagKey;

@implementation UIView (ObjectTagAdditions)
@dynamic objectTag;

- (id)objectTag {
    return objc_getAssociatedObject(self, ObjectTagKey);
}

- (void)setObjectTag:(id)newObjectTag {
    objc_setAssociatedObject(self, ObjectTagKey, newObjectTag, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

Register a custom app opening URL scheme

edit info.plist, add "URL types" section, add "URL Schemes" sub section.

Get current app version

NSDictionary *infoDictionary = [[NSBundle mainBundle] infoDictionary];
NSString *version = [infoDictionary objectForKey:@"CFBundleShortVersionString"];

Create repeating and non-repeating timers

NSTimer *timer;

// set `repeats` to NO if u don't want it to be repeated 
timer = [NSTimer scheduledTimerWithTimeInterval:3.0 target:self 
   selector:@selector(updateActivityIndicator:) userInfo:nil repeats:YES];

// stop the timer
[timer invalidate];

Compare string version

if ([onlineVersion compare:currentAppVersion options:NSNumericSearch] == NSOrderedDescending) {
	newAppVersion = onlineVersion;
}

Write multiple line of macro via

#define MAAssert(expression, ...) \
	do { \
		if(!(expression)) { \
			NSString *__MAAssert_temp_string = [NSString stringWithFormat: @"Assertion failure: %s in %s on line %s:%d. %@", #expression, __func__, __FILE__, __LINE__, [NSString stringWithFormat: @"" __VA_ARGS__]]; \
			NSLog(@"%@", __MAAssert_temp_string); \
			__crashreporter_info__ = [__MAAssert_temp_string UTF8String]; \
			abort(); \
		} \
	} while(0)

If an object is designed to be able to write to disk, it must implement NSCoding protocol.
NSAssert is used more then NSException
Variable inside block are retained, so if the block is retained by self, u should use weakSelf inside this block.
u can use keychain to save secure data like username/password, thus even the app is uninstalled, the data is still there.
use forwardingTargetForSelector: to redirect unknown message to new target.
set name to nil and object to nil to spy all notifications.
NSCache is like NSMutableDictionary but with builtin memory management.
use stringByEvaluatingJavascriptFromString: to communicate with javascript.
use + (void)load if u want to perform some init work on a category.
nil is like black hole, u can send any message to it without exception, while NSNull is like empty NSObject.

STjason/cocoa-tips