@property和setters and getters

Question

如果我创建一个@property并合成它,并创建一个getter和setter,如下所示:

#import <UIKit/UIKit.h>
{
    NSString * property;
}

@property NSString * property;

--------------------------------

@implementation

@synthesize property = _property

-(void)setProperty(NSString *) property
{
    _property = property;
}

-(NSString *)property
{
    return _property = @"something";
}

我是否正确地假设这个电话

-(NSString *)returnValue
{
    return self.property; // I know that this automatically calls the built in getter function that comes with synthesizing a property, but am I correct in assuming that I have overridden the getter with my getter? Or must I explicitly call my self-defined getter?
}

这个电话是一样的吗？

-(NSString *)returnValue
{
    return property; // does this call the getter function or the instance variable?
}

这个电话是一样的吗？

-(NSString *)returnValue
{
    return _property; // is this the same as the first example above?
}

Answer 1

您的代码存在许多问题,尤其是您无意中定义了两个不同的实例变量:property和_property.

Objective-C属性语法只是普通旧方法和实例变量的简写.您应该首先实现没有属性的示例:只使用常规实例变量和方法:

@interface MyClass {
    NSString* _myProperty;
}
- (NSString*)myProperty;
- (void)setMyProperty:(NSString*)value;

- (NSString*)someOtherMethod;
@end

@implementation MyClass

- (NSString*)myProperty {
    return [_myProperty stringByAppendingString:@" Tricky."];
}

- (void)setMyProperty:(NSString*)value {
    _myProperty = value; // Assuming ARC is enabled.
}

- (NSString*)someOtherMethod {
    return [self myProperty];
}

@end

要将此代码转换为使用属性,只需使用属性myProperty声明替换方法声明.

@interface MyClass {
    NSString* _myProperty;
}
@property (nonatomic, retain) NSString* myProperty

- (NSString*)someOtherMethod;
@end

...

实现保持不变,并且工作原理相同.

您可以选择在实现中合成属性,这允许您删除_myProperty实例变量声明和通用属性setter:

@interface MyClass
@property (nonatomic, retain) NSString* myProperty;
- (NSString*)someOtherMethod;
@end

@implementation MyClass
@synthesize myProperty = _myProperty; // setter and ivar are created automatically

- (NSString*)myProperty {
    return [_myProperty stringByAppendingString:@" Tricky."];
}

- (NSString*)someOtherMethod {
    return [self myProperty];
}

这些示例中的每一个在操作方式上都是相同的,属性语法只是简写,允许您编写较少的实际代码.

Answer 2

return self.property - 将调用您被覆盖的吸气剂.

return _property; - 直接访问属性的实例变量,不调用getter.

return property; - 实例变量.

编辑:我应该强调你将有两个不同的NSString变量 - property和_property.我假设你在这里测试边界而不是提供实际的生产代码.