Codethink

It’s been a bit quiet on the coding-front lately, so I thought I’d share a small handful of various utilities that I’ve developed over the past few weeks. None of them are particularly revolutionary, but they can certainly prove useful in the right situations. Anyways, in no particular order, I give you:

ScreenCaptureView

This bit of code allows you to easily capture the contents of any arbitrary UIView:

//  ScreenCaptureView.h
#import <UIKit/UIKit.h>

@interface ScreenCaptureView : UIView {
}

@property(retain) UIImage* currentScreen;
@property(assign) float frameRate;

@end


//  ScreenCaptureView.m
#import "ScreenCaptureView.h"
#import <QuartzCore/QuartzCore.h>

@implementation ScreenCaptureView

@synthesize currentScreen, frameRate;

- (id)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
        self.contentMode = UIViewContentModeRedraw;
        self.frameRate = 20.0f;//20 frames per seconds
    }
    return self;
}

- (void) drawRect:(CGRect)rect {
    CGContextRef context =  UIGraphicsGetCurrentContext();
    [self.layer renderInContext:context];
    CGImageRef cgImage = CGBitmapContextCreateImage(context);
    UIImage* background = [UIImage imageWithCGImage: cgImage];
    CGImageRelease(cgImage);
    self.currentScreen = background;
    
    [self performSelector:@selector(setNeedsDisplay) withObject:nil afterDelay:(1.0 / self.frameRate)];   //redraw at the specified framerate
}

- (void)dealloc {
    [super dealloc];
}
@end

The ‘ScreenCaptureView‘ class automatically captures its current contents (including any nested subviews) to a UIImage which it exposes through the ‘currentScreen‘ property. You can use this functionality to do things like generate screenshots of your application for use in help/tutorial (or promotional) content, and you can even pass the data as frames to an `AVCaptureSession` to create a live video of your app in action.

Update: An enhanced version of this class that includes the ability to record video is now available.

MultiplexingDelegate

For those rare cases when you want multiple delegate objects to be notified of a change/event in some object:

//  MultiplexingDelegate.h
#import <Foundation/Foundation.h>

@interface MultiplexingDelegate : NSObject {
    NSMutableArray* delegates;
}

- (void) addDelegate: (id) theDelegate;
- (void) removeDelegate: (id) theDelegate;
- (void) sendSelectorToDelegates: (SEL)selector withObject: (id)param1 andSecondObject: (id)param2
@end

//  MultiplexingDelegate.m
@implementation MultiplexingDelegate
- (id) init {
    if ((self = [super init])) {
        delegates = [[NSMutableArray alloc] initWithCapacity: 16];
    }
}

- (void) dealloc {
    [delegates release];
    [super dealloc]
}

- (void) addDelegate: (id) theDelegate {
    @synchronized(delegates) {
        if (theDelegate && ! [delegates containsObject: theDelegate]) {
            [delegates addObject: theDelegate];
        }
    }
}

- (void) removeDelegate: (id) theDelegate {
    @synchronized(delegates) {
        if (theDelegate && [delegates containsObject: theDelegate]) {
            [delegates removeObject: theDelegate];
        }
    }
}

- (void) sendSelectorToDelegates: (SEL)selector withObject: (id)param1 andSecondObject: (id)param2 {
    @synchronized(delegates) {
        for (id theDelegate in delegates) {
            if (param2) {
                [theDelegate performSelector:selector withObject:param1 withObject:param2];
            }
            else if (param1) {
                [theDelegate performSelector:selector withObject:param1];
            }
            else {
                [theDelegate performSelector:selector];
            }
        }
    }
}
@end

The ‘MultiplexingDelegate` class provides a generic starting point for creating delegates that conform to various protocols and support the multiplexing of events to any number of attached listeners. To use it you just need to create a new subclass of ‘MultiplexingDelegate‘ that implements whatever protocol you are interested in. For instance, here is a partial example of a multiplexing UISearchBarDelegate implementation:

//  MultiplexingSearchBarDelegate.h
#import <UIKit/UIKit.h>
#import "MultiplexingDelegate.h"

@interface MultiplexingSearchBarDelegate : MultiplexingDelegate<UISearchBarDelegate> {
}
@end

//  MultiplexingSearchBarDelegate.m
@implementation MultiplexingSearchBarDelegate
//add UISearchBarDelegate methods here, following a pattern like this:
- (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText {
    [self sendSelectorToDelegates: @selector(searchBar:textDidChange:) withObject: searchBar andSecondObject: searchText];
}

//or alternately/equivalently, a pattern like this:
- (BOOL)searchBar:(UISearchBar *)searchBar shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text {
    @synchronized(delegates) {
        for (id<UISearchBarDelegate> theDelegate in delegates) {
            [theDelegate searchBar:searchBar shouldChangeTextInRange: range replacementText: text];
        }
    }
}
@end

To use the ‘MultiplexingSearchBarDelegate‘ class you would create a single instance and add it as the delegate of your UISearchBar. Then you just register every other object that you want to receive UISearchBar events with the ‘MultiplexingSearchBarDelegate‘ (by using the ‘addDelegate:‘ method), and they will all receive event notifications from the UISearchBar. Simple, but powerful.

NSString+JavaAPI

There’s no getting around it, the standard NSString API just kind of sucks. Wouldn’t it be great if NSString supported an API that was more like what Java provides through its String class? Well now it can:

//  NSString+JavaAPI.h
#import <Foundation/Foundation.h>

@interface NSString (NSString_JavaAPI)
- (int) compareTo: (NSString*) comp;
- (int) compareToIgnoreCase: (NSString*) comp;
- (bool) contains: (NSString*) substring;
- (bool) endsWith: (NSString*) substring;
- (bool) startsWith: (NSString*) substring;
- (int) indexOf: (NSString*) substring;
- (int) indexOf:(NSString *)substring startingFrom: (int) index;
- (int) lastIndexOf: (NSString*) substring;
- (int) lastIndexOf:(NSString *)substring startingFrom: (int) index;
- (NSString*) substringFromIndex:(int)from toIndex: (int) to;
- (NSString*) trim;
- (NSArray*) split: (NSString*) token;
- (NSString*) replace: (NSString*) target withString: (NSString*) replacement;
- (NSArray*) split: (NSString*) token limit: (int) maxResults;
@end

//  NSString+JavaAPI.m
#import "NSString+JavaAPI.h"

@implementation NSString (NSString_JavaAPI)
- (int) compareTo: (NSString*) comp {
    NSComparisonResult result = [self compare:comp];
    if (result == NSOrderedSame) {
        return 0;
    }
    return result == NSOrderedAscending ? -1 : 1;
}

- (int) compareToIgnoreCase: (NSString*) comp {
    return [[self lowercaseString] compareTo:[comp lowercaseString]];
}

- (bool) contains: (NSString*) substring {
    NSRange range = [self rangeOfString:substring];
    return range.location != NSNotFound;
}

- (bool) endsWith: (NSString*) substring {
    NSRange range = [self rangeOfString:substring];
    return range.location == [self length] - [substring length];
}

- (bool) startsWith: (NSString*) substring {
    NSRange range = [self rangeOfString:substring];
    return range.location == 0;
}

- (int) indexOf: (NSString*) substring {
    NSRange range = [self rangeOfString:substring];
    return range.location == NSNotFound ? -1 : range.location;
}

- (int) indexOf:(NSString *)substring startingFrom: (int) index {
    NSString* test = [self substringFromIndex:index];
    return [test indexOf:substring];
}

- (int) lastIndexOf: (NSString*) substring {
    if (! [self contains:substring]) {
        return -1;
    }
    int matchIndex = 0;
    NSString* test = self;
    while ([test contains:substring]) {
        if (matchIndex > 0) {
            matchIndex += [substring length];
        }
        matchIndex += [test indexOf:substring];
        test = [test substringFromIndex: [test indexOf:substring] + [substring length]];
    }
    
    return matchIndex;
}

- (int) lastIndexOf:(NSString *)substring startingFrom: (int) index {
    NSString* test = [self substringFromIndex:index];
    return [test lastIndexOf:substring];
}

- (NSString*) substringFromIndex:(int)from toIndex: (int) to {
    NSRange range;
    range.location = from;
    range.length = to - from;
    return [self substringWithRange: range];
}

- (NSString*) trim {
    return [self stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
}

- (NSArray*) split: (NSString*) token {
    return [self split:token limit:0];
}

- (NSArray*) split: (NSString*) token limit: (int) maxResults {
    NSMutableArray* result = [NSMutableArray arrayWithCapacity: 8];
    NSString* buffer = self;
    while ([buffer contains:token]) {
        if (maxResults > 0 && [result count] == maxResults - 1) {
            break;
        }
        int matchIndex = [buffer indexOf:token];
        NSString* nextPart = [buffer substringFromIndex:0 toIndex:matchIndex];
        buffer = [buffer substringFromIndex:matchIndex + [token length]];
        if (nextPart) {
            [result addObject:nextPart];
        }
    }
    if ([buffer length] > 0) {
        [result addObject:buffer];
    }
    
    return result;
}

- (NSString*) replace: (NSString*) target withString: (NSString*) replacement {
    return [self stringByReplacingOccurrencesOfString:target withString:replacement];
}
@end

Note that this isn’t the complete Java String API (and also that `split()` does not support regular-expressions as it does in Java). It is just a subset consisting of the most useful Java API functions that do not have convenient analogs in the standard NSString API. Still, it makes a lot of common string manipulations a lot more straightforward than they otherwise would be.