点语法和KVC方法比较

Dot Syntax and Key-Value Coding

(最后一个例子看似很简单)

Objective-C’s dot syntax and key-value coding are orthogonal technologies. You can use key-value coding whether or not you use the dot syntax, and you can use the dot syntax whether or not you use KVC. Both, though, make use of a “dot syntax.” In the case of key-value coding, the syntax is used to delimit elements in a key path. Remember that when you access a property using the dot syntax, you invoke the receiver’s standard accessor methods.

You can use key-value coding methods to access a property, for example, given a class defined as follows:

@interface MyClass

@property NSString *stringProperty;

@property NSInteger integerProperty;

@property MyClass *linkedInstance;

@end

you could access the properties in an instance using KVC:

MyClass *myInstance = [[MyClass alloc] init];

NSString *string = [myInstance valueForKey:@"stringProperty"];

[myInstance setValue:@2 forKey:@"integerProperty"];

To illustrate the difference between the properties dot syntax and KVC key paths, consider the following.

MyClass *anotherInstance = [[MyClass alloc] init];

myInstance.linkedInstance = anotherInstance;

myInstance.linkedInstance.integerProperty = 2;

This has the same result as:

MyClass *anotherInstance = [[MyClass alloc] init];

myInstance.linkedInstance = anotherInstance;

[myInstance setValue:@2 forKeyPath:@"linkedInstance.integerProperty"];