Java 使用带有 switch 语句的枚举

2022-01-19 00:00:00 enums switch-statement java

我查看了与此问题类似的 SO 上的各种问答，但没有找到解决方案.

I've looked at various Q&As on SO similar to this question but haven't found a solution.

我所拥有的是一个枚举，它代表查看电视指南的不同方式...

What I have is an enum which represents different ways to view a TV Guide...

在 NDroid Application 类中

In the NDroid Application class

static enum guideView {
    GUIDE_VIEW_SEVEN_DAY,
    GUIDE_VIEW_NOW_SHOWING,
    GUIDE_VIEW_ALL_TIMESLOTS
}

...当用户更改视图时，事件处理程序从 0-2 接收 int，我想做这样的事情...

...when the user changes the view an event handler receives an int from 0-2 and I'd like to do something like this...

在 Android Activity onClick(DialogInterface dialog, int which) 事件处理程序

In an Android Activity onClick(DialogInterface dialog, int which) event handler

// 'which' is an int from 0-2
switch (which) {
    case NDroid.guideView.GUIDE_VIEW_SEVEN_DAY:
    ...
    break;
}

我已经习惯了 C# 枚举和 select/case 语句，它们允许像上面这样的事情，我知道 Java 做的事情不同，但我就是无法理解我需要做什么.

I'm used to C# enums and select/case statements which would allow something like the above and I know Java does things differently but I just can't make sense of what I need to do.

我将不得不求助于 if 语句吗?可能只有 3 个选择，所以我可以做到，但我想知道如何使用 Java 中的 switch-case 来完成.

Am I going to have to resort to if statements? There will likely only ever be 3 choices so I could do it but I wondered how it could be done with switch-case in Java.

编辑 抱歉，我没有完全扩展该问题，因为我将其视为通用 Java 问题.我已经添加到问题中以进一步解释.

EDIT Sorry I didn't completely expand on the issue as I was looking at it as being a generic Java issue. I've added to the question to explain a bit further.

没有任何特定于 Android 的东西，这就是为什么我没有将其标记为 Android，但枚举是在 Application 类中定义的，而我不想切换的代码在活动.枚举是静态的，因为我需要从多个活动中访问它.

There isn't anything that's Android specific which is why I didn't tag it as Android but the enum is defined in the Application class and the code where I wan't the switch is in an Activity. The enum is static as I need to access it from multiple Activities.

推荐答案

您缺少的部分是将整数转换为类型安全的枚举.Java 不会自动执行此操作.有几种方法可以解决这个问题:

The part you're missing is converting from the integer to the type-safe enum. Java will not do it automatically. There's a couple of ways you can go about this:

  1. 使用静态最终 int 列表而不是类型安全的枚举并打开您收到的 int 值(这是 Java 5 之前的方法)
  2. 打开指定的 id 值(如 heneryville 所述) 或枚举值的序数值；即 guideView.GUIDE_VIEW_SEVEN_DAY.ordinal()

  3. 判断int值代表的枚举值，然后开启枚举值.

  1. Use a list of static final ints rather than a type-safe enum and switch on the int value you receive (this is the pre-Java 5 approach)
  2. Switch on either a specified id value (as described by heneryville) or the ordinal value of the enum values; i.e. guideView.GUIDE_VIEW_SEVEN_DAY.ordinal()

  3. Determine the enum value represented by the int value and then switch on the enum value.

enum GuideView {
    SEVEN_DAY,
    NOW_SHOWING,
    ALL_TIMESLOTS
}

// Working on the assumption that your int value is 
// the ordinal value of the items in your enum
public void onClick(DialogInterface dialog, int which) {
    // do your own bounds checking
    GuideView whichView = GuideView.values()[which];
    switch (whichView) {
        case SEVEN_DAY:
            ...
            break;
        case NOW_SHOWING:
            ...
            break;
    }
}

您可能会发现编写自定义 valueOf 实现更有用/更不容易出错，该实现将整数值作为参数来解析适当的枚举值并让您集中检查边界.

You may find it more helpful / less error prone to write a custom valueOf implementation that takes your integer values as an argument to resolve the appropriate enum value and lets you centralize your bounds checking.

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