访问属性方法和类字段之间的区别(Objective-C) [英] Difference between accessing property methods and class fields (Objective-C)

问题描述

假设我有这段代码:

@interface Foo : NSObject {
    Bar *bar;
}

@property (retain, nonatomic) Bar *bar;

@end

使用这个字段/属性时，行之间有什么区别:

When using this field/property, is there any difference between lines:

[self.bar doStuff];

和

[bar doStuff];

?

在赋值时，property 方法会执行正确的保留，但是如上所述对属性的读取访问呢?有什么区别吗?

When doing assignment, property method will perform correct retaining, but what about the read access to the property, as described above? Is there any difference?

推荐答案

有很大的不同.[self.bar doStuff] 等价于 [[self bar] doStuff]

There is a big difference. [self.bar doStuff] is equivalent to [[self bar] doStuff]

[bar doStuff] 等价于 [self->bar doStuff]

前者使用accessor方法，后者只是直接访问实例变量bar.

The former uses the accessor method, the latter just accesses the instance variable bar directly.

如果您在 bar 属性上使用 @synthesize 指令，编译器将为您生成两个方法:

If you use the @synthesize directive on your bar property, the compiler will generate two methods for you:

- (void)setBar:(Bar*)b;
- (Bar*)bar;

另请注意，编译器生成的 setter 方法会保留您在 @property 声明中告诉它的 Bar 实例.

Also note, that the compiler generated setter method is retaining your Bar instance as you told it in the @property declaration.

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