ios - 延迟加载弱实例变量

Question

我想延迟加载一个实例变量 - 但如果它是从类外部设置的，我不想强​​烈指向它。

这可能吗？

例如：

@interface MyClass

@property (nonatomic,weak) LazyLoadedObject lazyObject;
@end

@implemetation MyClass

-(LazyLoadedObject *)lazyObject
{
  if (_lazyObject== nil)
  {
    //create a object and strongly point to it
    _lazyObject = [LazyLoadedObject new]
  }
  return _lazyObject;
}
@end

Answer 1

如果需要，为您的私有创建另一个属性，您将对其有很强的参考。

@property (nonatomic, weak) id lazyObject;
@property (nonatomic, strong) id privateLazyObject;

然后像这样实现getter：

- (id)lazyObject {
    // If contains value, return that, otherwise redirect to private strong value.
    return self->_lazyObject ?: self.privateLazyObject;
}

- (id)privateLazyObject {
    // Standard lazy getter
    if ( ! self->_privateLazyObject) {
        self.privateLazyObject = ...; // Strong ownership
    }
    return self->_privateLazyObject;
}

因此，当您设置 public 时lazyObject，请取消您的 private ：

- (void)setLazyObject:(id)lazyObject {
    self->_lazyObject = lazyObject; // Weak ownership
    self.privateLazyObject = nil; // Release any existing strong one.
}

Answer 2

制作该属性strong，因为您想“强烈指向它”。