不要忘记NSWindowController和NSViewController会释放它们所控制的NIB文件的顶级对象。

如果手动加载NIB文件，则在使用完该NIB的顶级对象后，需要负责释放它们。

在dealloc中清理。

这是最容易忘记的事情之一——尤其是在以150英里/小时的速度编码时。总是，总是，总是清理dealloc中的属性/成员变量。

我喜欢使用Objc 2属性-新的点表示法-所以这使得清理变得无痛。通常很简单:

- (void)dealloc
{
    self.someAttribute = NULL;
    [super dealloc];
}

这将为您处理发布，并将属性设置为NULL(我认为这是防御性编程——以防dealloc中的另一个方法再次访问成员变量——很少，但也可能发生)。

在10.5中打开GC后，就不再需要这么多了——但是你可能仍然需要清理你创建的其他资源，你可以在finalize方法中做这件事。

#import "MyClass.h"

@interface MyClass ()
- (void) someMethod;
- (void) someOtherMethod;
@end

@implementation MyClass

简单但经常被遗忘。根据规格:

一般来说，方法各不相同 具有相同选择器的类 (相同的名字)也必须共享 相同的返回值和参数类型。这 约束是由编译器施加的 允许动态绑定。

在这种情况下，所有相同的命名选择器，即使在不同的类中，也会被认为具有相同的返回/参数类型。这里有一个简单的例子。

@interface FooInt:NSObject{}
-(int) print;
@end

@implementation FooInt
-(int) print{
    return 5;
}
@end

@interface FooFloat:NSObject{}
-(float) print;
@end

@implementation FooFloat
-(float) print{
    return 3.3;
}
@end

int main (int argc, const char * argv[]) {

    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];    
    id f1=[[FooFloat alloc]init];
    //prints 0, runtime considers [f1 print] to return int, as f1's type is "id" and FooInt precedes FooBar
    NSLog(@"%f",[f1 print]);

    FooFloat* f2=[[FooFloat alloc]init];
    //prints 3.3 expectedly as the static type is FooFloat
    NSLog(@"%f",[f2 print]);

    [f1 release];
    [f2 release]
    [pool drain];

    return 0;
}   

功能性更强。

Objective-C是面向对象的语言，但是Cocoa框架是函数式风格的，并且在很多情况下是函数式设计的。

There is separation of mutability. Use immutable classes as primary, and mutable object as secondary. For instance, use NSArray primarily, and use NSMutableArray only when you need. There is pure functions. Not so many, buy many of framework APIs are designed like pure function. Look at functions such as CGRectMake() or CGAffineTransformMake(). Obviously pointer form looks more efficient. However indirect argument with pointers can't offer side-effect-free. Design structures purely as much as possible. Separate even state objects. Use -copy instead of -retain when passing a value to other object. Because shared state can influence mutation to value in other object silently. So can't be side-effect-free. If you have a value from external from object, copy it. So it's also important designing shared state as minimal as possible.

但是也不要害怕使用不纯函数。

There is lazy evaluation. See something like -[UIViewController view] property. The view won't be created when the object is created. It'll be created when caller reading view property at first time. UIImage will not be loaded until it actually being drawn. There are many implementation like this design. This kind of designs are very helpful for resource management, but if you don't know the concept of lazy evaluation, it's not easy to understand behavior of them. There is closure. Use C-blocks as much as possible. This will simplify your life greatly. But read once more about block-memory-management before using it. There is semi-auto GC. NSAutoreleasePool. Use -autorelease primary. Use manual -retain/-release secondary when you really need. (ex: memory optimization, explicit resource deletion)

IBOutlets

从历史上看，outlet的内存管理一直很差。 当前的最佳实践是将outlet声明为属性:

@interface MyClass :NSObject {
    NSTextField *textField;
}
@property (nonatomic, retain) IBOutlet NSTextField *textField;
@end

使用属性使内存管理语义清晰;如果使用实例变量综合，它还提供了一致的模式。