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....