lecture 4 : More Objective-C

Creating Objects

这件事困扰我一点时间了，ObjC没有一个Constructor的概念
而在Create Objects这件事上既有用过自己写的-init，还return instancetype，大概这个，也有用过一些Class Method，就是明确知道是+id类型的，Slides总结了

• alloc init来创建

NSMutableArray *cards = [[NSMutableArray alloc]init]

• Class Method来创建

NSString *moltuae = [NSString stringWithFormat:@“%d”, 42];NSString *a = @"hello world";//不过一般应该都用这个吧

• 也有init 和 Class Method共存的状况

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

老爷爷推荐alloc/init

• 利用objects的方法创建新的objects

NSString’s - (NSString *)stringByAppendingString:(NSString *)otherString; NSArray’s - (NSString *)componentsJoinedByString:(NSString *)separator; NSString’s & NSArray’s - (id)mutableCopy;//这个很有意思，将一个immutable的object变成一个mutable的新的object

• 这种则不是在创建object，虽然传递出object

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

除非NSArray不存在才会创建出NSArray，但是也是nil吧

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nil

nil很好用，只需注意struct状况

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id

id是一个很特殊很特殊的pointer， It means “pointer to an object of unknown/unspecified” type.

所以其实之前写的

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

能被完全写成

id a = [NS....];

id很有用，但是有危险。
因为给的信息很通用，则complier难以察觉出语法上的问题。
但是运行的时候可能就崩溃！

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

如果出现id,可以使用一下方法来保护自己：

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). 这里可以这样做，感觉就是把NSString class生成为一个class，然后再来测试，因为classes也是objects，老爷爷怕大家迷茫，让大家记住这个用法就好了if ([obj isKindOfClass:[NSString class]]) {  NSString *s = [(NSString *)obj stringByAppendingString:@”xyzzy”]; }

以下
这里的第一个shoot是没有参数的
第二个shootAt有一个参数，对于obj使用了target

Method有多个参数需要写成addCard:AtTop:类似

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:);

个人感觉这里的code将会有很大的用处，不过我目前还是暂时都不知了的状态

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 | | ... | ... | +----------------------------+---------------------------------------+

大概就是这样....
还有很多的Mutable版本，NSDate还有NSData...

再举了一些常用的Class Method

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Colors & Fonts

因为木有例子存在，一直都听的磕磕碰碰，充满了困意

让我假装直到每个有关的几件事吧

UIColor

• 可以设置alpha，我喜欢，透明度
• 可以用RGB，HSB，甚至图片patten来定义color
• [UIColor greenColor]有此种
• [UIColor lightTextColor]也有此种

Fonts

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

困意不断，我决定把NSMutableString以及这些相关的在demo时候再来复习/学习....
就是这么一个爱贪有趣的人....

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