Selector - a Selector is the name of a method. You're very familiar with these selectors: alloc, init, release, dictionaryWithObjectsAndKeys:, setObject:forKey:, etc. Note that the colon is part of the selector; it's how we identify that this method requires parameters. Also (though it's extremely rare), you can have selectors like this: doFoo:::. This is a method that takes three parameters, and you'd invoke it like [someObject doFoo:arg1 :arg2 :arg3]. There's no requirement that there be letters before each part of the selector components. As I said, this is extremely rare, and you will not find it used in the Cocoa frameworks. You can work with selectors directly in Cocoa. They have the type SEL: SEL aSelector = @selector(doSomething:) or SEL aSelector = NSSelectorFromString(@"doSomething:");
Message - a message is a selector and the arguments you are sending with it. If I say [dictionary setObject:obj forKey:key], then the "message" is the selector setObject:forKey: plus the arguments obj and key. Messages can be encapsulated in an NSInvocation object for later invocation. Messages are sent to a receiver. (ie, the object that "receives" the message).
Method - a method is a combination of a selector and an implementation (and accompanying metadata). The "implementation" is the actual block of code; it's a function pointer (an IMP). An actual method can be retrieved internally using a Method struct (retrievable from the runtime).
Method Signature - a method signature represents the data types returned by and accepted by a method. They can be represented at runtime via an NSMethodSignature and (in some cases) a raw char*.
Implementation - the actual executable code of a method. Its type at runtime is an IMP, and it's really just a function pointer. iOS 4.3 includes a new ability to turn a block into an IMP. This is really cool.
source: https://stackoverflow.com/questions/5608476/whats-the-difference-between-a-method-and-a-selector
未指定初始值的变量都会被初始化为nil
cannot call retain, release, autorelease, and retainCount
use @autoreleasepool to replace NSAutoareleasePool
naming convention： 特殊方法族： （alloc, copy, mutableCopy, new, init）以此为开头的方法表示调用者必须有被创建者的所有权， 其中init 必须为实例方法
不可explicitly call dealloc [super dealloc], because ARC will take care of memory release, but you can use free for null pointers
@autoreleasepool 可以嵌套使用
weak reference __weak
未加__weak，or __strong 为strong reference（reference count +1 when being referred to)
while weak reference will not affect the reference counts, and will be automatically set to nil when the referencing instance is released (opposite to strong reference which will still hold the instance)
lifetime qualifier
__weak, __strong, __autoreleasing, __unsafe_unretained
target : the receiver of an action message
action : the message a control send to the target(stored a SEL type)
- (void)capitalizeWord:(id)sender
- (IBAction)deleteRecord:(id)sender
- (void)action:(id)sender forEvent:(UIEvent *)event //UIKit
IBAction is a type qualifier the sender parameter identifies the control sending the action message
to set the target and action programmatically you need to definde the setAction and setTarget method to send messages to a control or to cell object
- (void)setTarget:(id)anObject;
- (void)setAction:(SEL)aSelector;
to use this methods
[aCell setTarget: myController]
[aControl setAction: @selector(deleteRecord)]
http://www.cocoachina.com/ios/20150731/12819.html
深入理解GCD https://justinyan.me/post/2420 Runloop https://juejin.im/post/5a352c6c5188251fbd33b345
https://www.jianshu.com/p/ea3f90cc744b
https://www.cnblogs.com/lbjventure/p/4343370.html
https://github.com/kisanzxy/YYModel YYModel 详解 https://www.jianshu.com/p/25e678fa43d3
###YYCatche详解 https://juejin.im/post/5a657a946fb9a01cb64ee761
https://www.devtalking.com/articles/you-should-to-know-property/
getter and setter . operation when instance variables are not explicitly declared, a variable start with "_" will autamatically be declared.
###ios开发必备知识点 https://www.jianshu.com/p/ea10e5a03c70