dev tips

横竖屏:
UIInterfaceOrientation orientation = [[UIApplication sharedApplication] statusBarOrientation];
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java里的toString()相当于NSObject的-(NSString*)description;
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addSubView时没置顶：
    //CGAffineTransform myTransform = CGAffineTransformMakeTranslation(0.0, -20.0);
    //[self.navigationController.view setTransform:myTransform];
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notification机制：
注册：[[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(someFunction)
                                                     name:@"notificationIdentifier"
                                                   object:nil];
发送：[[NSNotificationCenter defaultCenter] postNotificationName:@"notificationIdentifier"  object:nil]];
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NSObject的Observer机制
可以对任何一个NSObject的某个属性注册一个Observer：
[someNSObject addObserver:self
                           forKeyPath:@"someProperty"
                              options:(NSKeyValueObservingOptionNew)
                              context:NULL];
当someNSObject的someProperty值发生变化时，会自动调用当前类的
- (void)observeValueForKeyPath:(NSString *)keyPath
  ofObject:(id)object
                        change:(NSDictionary *)change
                       context:(void *)context{}
其中改变后的新值会放在change里面。也可以用NSKeyValueObservingOptionOld使改变前的值放在change里。两者或运算则新值、旧值都放change里
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遍历Documents目录：

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *directoryPath = [paths objectAtIndex:0];

    NSArray *fileNames = [[NSFileManager defaultManager] contentsOfDirectoryAtPath:directoryPath error:nil];
    NSMutableArray *filePaths = [NSMutableArray arrayWithCapacity:[fileNames count]];
    for (NSString * fileName in fileNames) {
    }

后台下载：

downloadRequest = [[ASIHTTPRequest requestWithURL:task.url] retain];
    [downloadRequest setShouldContinueWhenAppEntersBackground:YES];
    [downloadRequest setShouldAttemptPersistentConnection:YES];
    [downloadRequest setDownloadProgressDelegate:self];
    [downloadRequest setNumberOfTimesToRetryOnTimeout:2];
    [downloadRequest setAllowResumeForFileDownloads:YES];
    NSString *savePath = [[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"] 
                          stringByAppendingPathComponent:task.title];
    [downloadRequest setTemporaryFileDownloadPath:[savePath stringByAppendingPathExtension:@"download"]];
    [downloadRequest setDownloadDestinationPath:savePath];
    
    [downloadRequest setDelegate:self];
    [downloadRequest startAsynchronous];

SynthesizeSingleton

#define SYNTHESIZE_SINGLETON_FOR_CLASS(classname) \
 \
static classname *shared##classname = nil; \
 \
+ (classname *)shared##classname \
{ \
	@synchronized(self) \
	{ \
		if (shared##classname == nil) \
		{ \
			shared##classname = [[self alloc] init]; \
		} \
	} \
	 \
	return shared##classname; \
} \
 \
+ (id)allocWithZone:(NSZone *)zone \
{ \
	@synchronized(self) \
	{ \
		if (shared##classname == nil) \
		{ \
			shared##classname = [super allocWithZone:zone]; \
			return shared##classname; \
		} \
	} \
	 \
	return nil; \
} \
 \
- (id)copyWithZone:(NSZone *)zone \
{ \
	return self; \
} \
 \
- (id)retain \
{ \
	return self; \
} \
 \
- (NSUInteger)retainCount \
{ \
	return NSUIntegerMax; \
} \
 \
- (oneway void)release \
{ \
} \
 \
- (id)autorelease \
{ \
	return self; \
}