Java 到 C#:在泛型中扩展 [英] Java to C#: Extends in Generic

问题描述

我正在尝试将此 Java (Android) 代码转换为 c# (MonoDroid)，但我不明白

I am trying to convert this Java (Android) code to c# (MonoDroid) but I don't understand the <Item extends OverlayItem>

public class BalloonOverlayView<Item extends OverlayItem> extends FrameLayout

推荐答案

它正在向类型参数添加约束.它类似于 C# 中的 where 子句.

It's adding a constraint to the type parameter. It's analogous to the where clause in C#.

在 Java 中，您有:

In Java, you have:

public class BalloonOverlayView<Item extends OverlayItem> extends FrameLayout

其中 Item 是一个类型参数，它必须子类化或实现类型 OverlayItem.在 C# 中，这将被写为:

Where Item is a type parameter that must subclass or implement type OverlayItem. In C# this would be written as:

public class BalloonOverlayView<Item> : FrameLayout where Item : OverlayItem

您可以看到约束是如何移动到最后的，但其他方面类似.在 C# 中的常见做法是命名带有 前缀的类型参数T，所以我会推荐名称 TItem 像这样:

You can see how the constraint is moved to the end, but otherwise analogous. It is very much common practice in C# to name type parameters prefixed with a T, so I would recommend the name TItem like so:

public class BalloonOverlayView<TItem> : FrameLayout where TItem : OverlayItem

这有助于明确类型参数和普通类型之间非常重要的区别.

This helps make clear the pretty important distinction between type parameters and ordinary types.

关于何时想要使用这样的类型约束的讨论，我在之前的回答中详细介绍了这一点.

For a discussion on when you'd want to use type constraints like this, I go into this at length in a previous answer.

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