Spotify's invocation grabber, with some magic tricks

gistfile3.m

// A
+(UIView*)flashAt:(CGRect)r in:(UIView*)parent color:(UIColor*)color;
{
	float duration = 0.5;
	UIView *flash = [[[UIView alloc] initWithFrame:r] autorelease];
	flash.backgroundColor = color;
	[parent addSubview:flash];
	[[flash invokeAfter:duration+0.1] removeFromSuperview];
		
	[UIView beginAnimations:@"SPFlash" context:NULL];
	[UIView setAnimationDuration:duration];
	flash.alpha = 0.0;
	[UIView commitAnimations];
	return flash;
}

// B
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
	
	// Force the animation to happen by calling this method again after a small
	// delay - see http://blog.instapaper.com/post/53568356
	[[self nextRunloop] delayedTableViewDidSelectRowAtIndexPath: indexPath];
}

// C
[[tableView invokeAfter:0.15] selectRowAtIndexPath:indexPath animated:YES scrollPosition:UITableViewScrollPositionNone];
[[tableView invokeAfter:0.30] deselectRowAtIndexPath:indexPath animated:YES];
[[tableView invokeAfter:0.45] selectRowAtIndexPath:indexPath animated:YES scrollPosition:UITableViewScrollPositionNone];

gistfile4.m

@interface MyClass : NSObject
-(BOOL)areTheNewViewersGoneYet:(Duck*)duck;
@end
...
MyClass *myInstance = [[MyClass alloc] init];
id invocationGrabber = [[[SPInvocationGrabber alloc] initWithTarget:myInstance] autorelease];


[invocationGrabber areTheNewViewersGoneYet:[Duck yellowDuck]]; // line 9


NSInvocation *invocationForAreTheNewViewersGoneYet = [invocationGrabber invocation];

main.m

#import <Cocoa/Cocoa.h>
#import "NSObject+SPInvocationGrabbing.h"

@interface Foo : NSObject {
    int a;
}
-(void)startIt;
-(void)theBackgroundStuff;
-(void)theForegroundStuff;
@end

@implementation Foo
-(void)startIt;
{
    NSLog(@"Starting out on the main thread...");
    a = 3;
    [[self inBackground] theBackgroundStuff];
}
-(void)theBackgroundStuff;
{
    NSLog(@"Woah, this is a background thread!");
    a += 6;
    [[self onMainAsync:YES] theForegroundStuff];
}
-(void)theForegroundStuff;
{
    NSLog(@"Hey presto: %d", a);
}
@end

int main() {
    NSAutoreleasePool *pool = [NSAutoreleasePool new];
    Foo *foo = [Foo new];
    [foo startIt];
    [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:1]];
    [pool release];
    return 0;
}

NSObject+SPInvocationGrabbing.h

#import <Foundation/Foundation.h>

@interface SPInvocationGrabber : NSObject {
    id _object;
    NSInvocation *_invocation;
    int frameCount;
    char **frameStrings;
    BOOL backgroundAfterForward;
    BOOL onMainAfterForward;
    BOOL waitUntilDone;
}
-(id)initWithObject:(id)obj;
-(id)initWithObject:(id)obj stacktraceSaving:(BOOL)saveStack;
@property (readonly, retain, nonatomic) id object;
@property (readonly, retain, nonatomic) NSInvocation *invocation;
@property BOOL backgroundAfterForward;
@property BOOL onMainAfterForward;
@property BOOL waitUntilDone;
-(void)invoke; // will release object and invocation
-(void)printBacktrace;
-(void)saveBacktrace;
@end

@interface NSObject (SPInvocationGrabbing)
-(id)grab;
-(id)invokeAfter:(NSTimeInterval)delta;
-(id)nextRunloop;
-(id)inBackground;
-(id)onMainAsync:(BOOL)async;
@end

NSObject+SPInvocationGrabbing.m

#import "NSObject+SPInvocationGrabbing.h"
#import <execinfo.h>

#pragma mark Invocation grabbing
@interface SPInvocationGrabber ()
@property (readwrite, retain, nonatomic) id object;
@property (readwrite, retain, nonatomic) NSInvocation *invocation;

@end

@implementation SPInvocationGrabber
- (id)initWithObject:(id)obj;
{
	return [self initWithObject:obj stacktraceSaving:YES];
}

-(id)initWithObject:(id)obj stacktraceSaving:(BOOL)saveStack;
{
	self.object = obj;

	if(saveStack)
		[self saveBacktrace];

	return self;
}
-(void)dealloc;
{
	free(frameStrings);
	self.object = nil;
	self.invocation = nil;
	[super dealloc];
}
@synthesize invocation = _invocation, object = _object;

@synthesize backgroundAfterForward, onMainAfterForward, waitUntilDone;
- (void)runInBackground;
{
	NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
	@try {
		[self invoke];
	}
	@finally {
		[pool drain];
	}
}


- (void)forwardInvocation:(NSInvocation *)anInvocation {
	[anInvocation retainArguments];
	anInvocation.target = _object;
	self.invocation = anInvocation;
	
	if(backgroundAfterForward)
		[NSThread detachNewThreadSelector:@selector(runInBackground) toTarget:self withObject:nil];
	else if(onMainAfterForward)
        [self performSelectorOnMainThread:@selector(invoke) withObject:nil waitUntilDone:waitUntilDone];
}
- (NSMethodSignature *)methodSignatureForSelector:(SEL)inSelector {
	NSMethodSignature *signature = [super methodSignatureForSelector:inSelector];
	if (signature == NULL)
		signature = [_object methodSignatureForSelector:inSelector];
    
	return signature;
}

- (void)invoke;
{

	@try {
		[_invocation invoke];
	}
	@catch (NSException * e) {
		NSLog(@"SPInvocationGrabber's target raised %@:\n\t%@\nInvocation was originally scheduled at:", e.name, e);
		[self printBacktrace];
		printf("\n");
		[e raise];
	}

	self.invocation = nil;
	self.object = nil;
}

-(void)saveBacktrace;
{
  void *backtraceFrames[128];
  frameCount = backtrace(&backtraceFrames[0], 128);
  frameStrings = backtrace_symbols(&backtraceFrames[0], frameCount);
}
-(void)printBacktrace;
{
	for(int x = 3; x < frameCount; x++) {
		if(frameStrings[x] == NULL) { break; }
		printf("%s\n", frameStrings[x]);
	}
}
@end

@implementation NSObject (SPInvocationGrabbing)
-(id)grab;
{
	return [[[SPInvocationGrabber alloc] initWithObject:self] autorelease];
}
-(id)invokeAfter:(NSTimeInterval)delta;
{
	id grabber = [self grab];
	[NSTimer scheduledTimerWithTimeInterval:delta target:grabber selector:@selector(invoke) userInfo:nil repeats:NO];
	return grabber;
}
- (id)nextRunloop;
{
	return [self invokeAfter:0];
}
-(id)inBackground;
{
    SPInvocationGrabber *grabber = [self grab];
	grabber.backgroundAfterForward = YES;
	return grabber;
}
-(id)onMainAsync:(BOOL)async;
{
    SPInvocationGrabber *grabber = [self grab];
	grabber.onMainAfterForward = YES;
    grabber.waitUntilDone = !async;
	return grabber;
}

@end