C# 查看 RadioButtonList 是否具有选定值的最佳方法是什么？

What is the best way to see if a RadioButtonList has a selected value?

提问by John Bubriski

I am using:

我在用：

if (RadioButtonList_VolunteerType.SelectedItem != null)

or how about:

或者怎么样：

if (RadioButtonList_VolunteerType.Index >= 0)

or how about (per Andrew Hare's answer):

或者怎么样（根据 Andrew Hare 的回答）：

if (RadioButtonList_VolunteerType.Index > -1)

To those who may read this question, the following is not a valid method. As Keltex pointed out, the selected value could be an empty string.

对于可能阅读此问题的人，以下不是有效方法。正如 Keltex 指出的那样，选定的值可能是一个空字符串。

if (string.IsNullOrEmpty(RadioButtonList_VolunteerType.SelectedValue))

采纳答案by Martin Clarke

In terms of readability they all lack something for me. This seems like a good candidate for an extension method.

就可读性而言，它们对我来说都缺乏一些东西。这似乎是扩展方法的一个很好的候选者。

public static class MyExtenstionMethods 
{   
  public static bool HasSelectedValue(this RadioButtonList list) 
  {
    return list.SelectedItem != null;
  }
}


...

if (RadioButtonList_VolunteerType.HasSelectedValue)
{
 // do stuff
}

回答by Andrew Hare

Those are all valid and perfectly legitimate ways of checking for a selected value. Personally I find

这些都是检查选定值的有效且完全合法的方法。个人觉得

RadioButtonList_VolunteerType.SelectedIndex > -1

to be the clearest.

要最清楚。

回答by Keltex

I recommend:

我建议：

RadioButtonList_VolunteerType.SelectedIndex>=0. 

According to the Microsoft Documentation:

根据微软文档：

The lowest ordinal index of the selected items in the list. The default is -1, which indicates that nothing is selected.

列表中所选项目的最低序数索引。默认值为 -1，表示未选择任何内容。

string.IsNullOrEmpty(RadioButtonList_VolunteerType.SelectedValue) will not always workas you can have a ListItem with an empty value:

string.IsNullOrEmpty(RadioButtonList_VolunteerType.SelectedValue)并不总是有效，因为您可以拥有一个空值的 ListItem：

<asp:ListItem Value=''>This item has no value</asp:ListItem>

回答by Scotty.NET

The question revolves more around whether to check for null or check value of an int. Martin's great extension method could also be written:

问题更多地围绕是检查 null 还是检查 int 的值。Martin 伟大的扩展方法也可以写成：

public static bool HasSelectedValue(this ListControl list)
{
    return list.SelectedIndex >= 0;
}

The MSDN documentation for a ListControl states:

ListControl 的 MSDN 文档指出：

Default for SelectedItem is null.

Default for SelectedIndex is -1.

SelectedItem 的默认值为 null。

SelectedIndex 的默认值为 -1。

So either are valid ways and both work. The question is which is the best way. I'm guessing SelectedIndex as it is a value type operation rather than reference type operation. But I don't have anything to back that up with.

所以要么是有效的方法，要么都有效。问题是哪种方法最好。我猜 SelectedIndex 因为它是值类型操作而不是引用类型操作。但我没有任何支持。