我看到的苹果提供的示例将App委托视为一个全局数据存储，一种数据管理器。这是错误的。创建一个单例，并在App委托中实例化它，但不要将App委托用作应用程序级事件处理以外的任何东西。我衷心赞同这篇博客文章中的建议。这条线索暴露了我。

使用NSAssert和朋友。 我一直使用nil作为有效对象…特别是发送消息给nil在Obj-C中是完全有效的。 然而，如果我真的想确定一个变量的状态，我使用NSAssert和NSParameterAssert，这有助于轻松跟踪问题。

黄金法则:如果你分配了，那么你就释放了!

更新:除非你正在使用ARC

声明属性

对于所有属性，您通常应该使用Objective-C 2.0声明属性特性。如果它们不是公共的，将它们添加到类扩展中。使用声明的属性使内存管理语义立即清晰，并使您更容易检查dealloc方法——如果您将属性声明分组在一起，您可以快速扫描它们并与dealloc方法的实现进行比较。

在不将属性标记为“nonatomic”之前，您应该仔细考虑一下。正如《Objective C编程语言指南》所指出的，属性在默认情况下是原子的，并且会产生相当大的开销。此外，简单地将所有属性都设置为原子化并不能使应用程序具有线程安全性。当然，还要注意，如果你没有指定“nonatomic”，并且实现你自己的访问方法(而不是合成它们)，你必须以原子的方式实现它们。

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)

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;
}