Custom setter and getter

简单的是最容易忽略的。

不是最好，但你必须理解的写法

@property (nonatomic, retain) UILabel *someLabel;

-(UILabel *)someLabel
{
    return _someLabel;
}

- (void)setSomeLabel:(UILabel *)someLabel
{
    if (someLabel != _someLabel) {
        [_someLabel release];
        _someLabel = [someLabel retain];
    }
}

如果你自定义了setter，推荐使用release释放对象

可能引起crash：

- (void)delloc
{
    self.someLabel = nil;
    [super delloc];
}

推荐：

- (void)delloc
{
    [_someLabel release];
    _someLabel = nil; 
    [super delloc];
}

在Apple官方文档中并不推荐在init和delloc中用Accessor方法，原因Apple也没有解释。

Don’t Use Accessor Methods in Initializer Methods and dealloc.
The only places you shouldn’t use accessor methods to set an instance variable are in initializer methods and dealloc.

stackoverflow中有人提到self.variable = nil可以避免悬挂指针引起的crash，但是如果setter是自定义的，那么[variable release]是更合适的选择。

Typically, you would either use self.variable = nil which has the benefit that it also sets the variable to nil (avoiding crashes due to dangling pointers), or [variable release] which is the fastest and may be more appropriate in a dealloc method if your setter has custom logic.

参考

• Objective-C Custom Setter
• Advanced Memory Management Programming Guide
• Why shouldn't I use the getter to release a property in objective-c?