Question

来自MapBox的Route-Me我看到iVars的实现方式如下：

@implementation RMMapView
{
    BOOL _delegateHasBeforeMapMove;
    BOOL _delegateHasAfterMapMove;
    BOOL _delegateHasBeforeMapZoom;
    BOOL _delegateHasAfterMapZoom;
    BOOL _delegateHasMapViewRegionDidChange;
    BOOL _delegateHasDoubleTapOnMap;
    BOOL _delegateHasSingleTapOnMap;
    BOOL _delegateHasSingleTapTwoFingersOnMap;
    BOOL _delegateHasLongSingleTapOnMap;
    BOOL _delegateHasTapOnAnnotation;
    BOOL _delegateHasDoubleTapOnAnnotation;
    BOOL _delegateHasTapOnLabelForAnnotation;
    BOOL _delegateHasDoubleTapOnLabelForAnnotation;
    BOOL _delegateHasShouldDragMarker;
    BOOL _delegateHasDidDragMarker;
    BOOL _delegateHasDidEndDragMarker;
    BOOL _delegateHasLayerForAnnotation;
    BOOL _delegateHasWillHideLayerForAnnotation;
    BOOL _delegateHasDidHideLayerForAnnotation;

    BOOL _constrainMovement;
    RMProjectedRect _constrainingProjectedBounds;

    float _lastZoom;
    CGPoint _lastContentOffset, _accumulatedDelta;
    BOOL _mapScrollViewIsZooming;
}

也就是说，它是在.m文件而不是.h文件中声明的。如果我对这个RMMapView进行子类化，我看不到这些iVars。有没有办法让它在子类中可见，而不是在世界上？

我打算保留原始代码，因此选择子类并从那里修改行为。但也许只是直接更改文件并通过git从主存储库更新代码是一种更好的方法吗？

Answer 1

在Objective-C中（与其他OO语言一样），大多数开发人员认为实例变量是定义类的实现细节。不应该由其他类直接访问它们。

在这种情况下，实例中声明了实例变量，这是RMMapView的作者不希望将变量暴露给外部代码的强烈暗示。

Answer 2

如果您确实希望子类可以看到实例变量，则需要在@interface中声明它们，而不是@implementation。

@interface RMMapView : NSObject
{
@protected
    BOOL _delegateHasBeforeMapMove;
    BOOL _delegateHasAfterMapMove;
    BOOL _delegateHasBeforeMapZoom;
    BOOL _delegateHasAfterMapZoom;
    BOOL _delegateHasMapViewRegionDidChange;
    BOOL _delegateHasDoubleTapOnMap;
    BOOL _delegateHasSingleTapOnMap;
    BOOL _delegateHasSingleTapTwoFingersOnMap;
    BOOL _delegateHasLongSingleTapOnMap;
    BOOL _delegateHasTapOnAnnotation;
    BOOL _delegateHasDoubleTapOnAnnotation;
    BOOL _delegateHasTapOnLabelForAnnotation;
    BOOL _delegateHasDoubleTapOnLabelForAnnotation;
    BOOL _delegateHasShouldDragMarker;
    BOOL _delegateHasDidDragMarker;
    BOOL _delegateHasDidEndDragMarker;
    BOOL _delegateHasLayerForAnnotation;
    BOOL _delegateHasWillHideLayerForAnnotation;
    BOOL _delegateHasDidHideLayerForAnnotation;

    BOOL _constrainMovement;
    RMProjectedRect _constrainingProjectedBounds;

    float _lastZoom;
    CGPoint _lastContentOffset, _accumulatedDelta;
    BOOL _mapScrollViewIsZooming;
}

顶部的@protected限定了可见性，它也可以是@public或@private。 @protected是默认设置，但最好明确地将其显示为显示您故意希望这些ivars对子类可见。

IVar的Objective-C继承

2 个答案: