Creating Objects

這件事困擾我一點時間了，ObjC沒有一個Constructor的概念
而在Create Objects這件事上既有用過自己寫的-init，還return instancetype，大概這個，也有用過一些Class Method，就是明確知道是+id類型的，Slides總結(jié)了

• alloc init來創(chuàng)建

NSMutableArray *cards = [[NSMutableArray alloc]init]

• Class Method來創(chuàng)建

NSString *moltuae = [NSString stringWithFormat:@“%d”, 42];NSString *a = @"hello world";//不過一般應(yīng)該都用這個吧

• 也有init 和 Class Method共存的狀況

[NSString stringWithFormat:...] same as [[NSString alloc] initWithFormat:...]

老爺爺推薦alloc/init

• 利用objects的方法創(chuàng)建新的objects

NSString’s - (NSString *)stringByAppendingString:(NSString *)otherString; NSArray’s - (NSString *)componentsJoinedByString:(NSString *)separator; NSString’s & NSArray’s - (id)mutableCopy;//這個很有意思，將一個immutable的object變成一個mutable的新的object

• 這種則不是在創(chuàng)建object，雖然傳遞出object

NSArray’s - (id)lastObject; NSArray’s - (id)objectAtIndex:(int)index;

除非NSArray不存在才會創(chuàng)建出NSArray，但是也是nil吧

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nil

nil很好用，只需注意struct狀況

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id

id是一個很特殊很特殊的pointer， It means “pointer to an object of unknown/unspecified” type.

所以其實之前寫的

NSString *a = [NS....];

能被完全寫成

id a = [NS....];

id很有用，但是有危險。
因為給的信息很通用，則complier難以察覺出語法上的問題。
但是運行的時候可能就崩潰！

Really all object pointers (e.g. NSString *) are treated like id at runtime.
But at compile time, if you type something NSString * instead of id, the compiler can help you.

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Introspection

如果出現(xiàn)id,可以使用一下方法來保護自己：

isKindOfClass (inheritance included) isMemberOfClass (no inheritance) respondsToSelector Class testing methods take a Class You get a Class by sending the class method class to a class (not the instance method class). 這里可以這樣做，感覺就是把NSString class生成為一個class，然后再來測試，因為classes也是objects，老爺爺怕大家迷茫，讓大家記住這個用法就好了if ([obj isKindOfClass:[NSString class]]) {  NSString *s = [(NSString *)obj stringByAppendingString:@”xyzzy”]; }

以下
這里的第一個shoot是沒有參數(shù)的
第二個shootAt有一個參數(shù)，對于obj使用了target

Method有多個參數(shù)需要寫成addCard:AtTop:類似

if ([obj respondsToSelector:@selector(shoot)]) {[obj shoot]; } else if ([obj respondsToSelector:@selector(shootAt:)]) {[obj shootAt:target]; } SEL is the Objective-C “type” for a selector SEL shootSelector = @selector(shoot); SEL shootAtSelector = @selector(shootAt:); SEL moveToSelector = @selector(moveTo:withPenColor:);

個人感覺這里的code將會有很大的用處，不過我目前還是暫時都不知了的狀態(tài)

If you have a SEL, you can also ask an object to perform it ...Using the performSelector: or performSelector:withObject: methods in NSObject [obj performSelector:shootSelector]; [obj performSelector:shootAtSelector withObject:coordinate];Using makeObjectsPerformSelector: methods in NSArray [array makeObjectsPerformSelector:shootSelector]; // cool, huh? [array makeObjectsPerformSelector:shootAtSelector withObject:target]; // target is an id  In UIButton, - (void)addTarget:(id)anObject action:(SEL)action ...; [button addTarget:self action:@selector(digitPressed:) ...];

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Foundations

+----Primitive Data Types ---+-----Foundation Data Structures--------+ | int | NSNumber - generic | | double | NSString | | float | NSArray | | struct | NSSet | | struct | NSDictionary | | ... | ... | +----------------------------+---------------------------------------+

大概就是這樣....
還有很多的Mutable版本，NSDate還有NSData...

再舉了一些常用的Class Method

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Colors & Fonts

因為木有例子存在，一直都聽的磕磕碰碰，充滿了困意

讓我假裝直到每個有關(guān)的幾件事吧

UIColor

• 可以設(shè)置alpha，我喜歡，透明度
• 可以用RGB，HSB，甚至圖片patten來定義color
• [UIColor greenColor]有此種
• [UIColor lightTextColor]也有此種

Fonts

UIFont *font = [UIFont preferredFontForTextStyle:UIFontTextStyleBody];//用到user's contents里+ (UIFont *)systemFontOfSize:(CGFloat)pointSize; + (UIFont *)boldSystemFontOfSize:(CGFloat)pointSize;//用到button之類的

困意不斷，我決定把NSMutableString以及這些相關(guān)的在demo時候再來復(fù)習(xí)/學(xué)習(xí)....
就是這么一個愛貪有趣的人....

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