调用方法调用的独特方法 [英] Unique way of invoking a method call

问题描述

我试图理解为什么等号后需要以下方法调用(MKPinAnnotationView *).

I am trying to understand why the following method call needs (MKPinAnnotationView *) after the equal sign.

此方法的定义可以在MKMapView.h标头中找到.

This method's definition can be found in the MKMapView.h header.

/ Used by the delegate to acquire an already allocated annotation view, in lieu of allocating a new one.
- (MKAnnotationView *)dequeueReusableAnnotationViewWithIdentifier:(NSString *)identifier;

当我查看此方法的示例调用时，会看到以下语法:

When I look at the sample calls for this method I see the following syntax:

MKPinAnnotationView *view = (MKPinAnnotationView*)[mapView dequeueReusableAnnotationViewWithIdentifier:kPinIdentifier];

如果该方法返回MKAnnotationView对象；为什么我不能编写以下方法调用:

If the method returns MKAnnotationView object; why can I not write the following method call:

MKPinAnnotationView *view = [mapView dequeueReusableAnnotationViewWithIdentifier:kPinIdentifier];

如果在等号的左边，我有一个MKAnnotationView对象，那么等号之后和方法调用之前(MKPinAnnotationView *)的作用是什么?

If to the left of the equal sign I have an MKAnnotationView object, what is the purpose of the (MKPinAnnotationView*) after the equal sign and before the method call?

此外，强制使用等号后的(MKPinAnnotationView *)块的方法定义是什么?

Also, what is it on the method's definition that is enforcing the use of the (MKPinAnnotationView*) piece after the equal sign?

幸运的是，该代码使用特殊的语法，但是由于我从未见过这种类型的方法调用，因此我的头想知道在方法调用和初始化程序方面是否缺少其他内容.

Fortunately the code works with the special syntax, but since I have never seen this type of method call, my head is wondering if I am missing something else when it comes to method calls and initializers.

推荐答案

这是类型转换.该方法返回MKAnnotationView *，但是调用方将其强制转换为MKPinAnnotationView *.调用者假定这些是兼容类型.例如，MKPinAnnotationView可能是MKAnnotationView的子类.

It's a type cast. The method returns a MKAnnotationView *, but the caller is casting it to a MKPinAnnotationView *. The caller is assuming these are compatible types. For example maybe MKPinAnnotationView is a subclass of MKAnnotationView.

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