C# LINQ：使用 Lambda 表达式获取 CheckBoxList 的所有选定值
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LINQ: Get all selected values of a CheckBoxList using a Lambda expression
提问by p.campbell
Consider a scenario where you want to retrieve a Listor IEnumerableof the values of all the selected checkboxes in an <asp:CheckBoxList>.
考虑要检索的场景List或IEnumerable在所有选中的复选框的值<asp:CheckBoxList>。
Here's the current implementation:
这是当前的实现：
IEnumerable<int> allChecked = (from item in chkBoxList.Items.Cast<ListItem>()
where item.Selected
select int.Parse(item.Value));
Question: How would you improve this LINQ query using a lambda expression or lambda syntax?
问题：您将如何使用 lambda 表达式或 lambda 语法改进此 LINQ 查询？
采纳答案by Andrew Hare
You areusing lambda expressions - they are just concealed by your use of C#'s query operators.
您正在使用 lambda 表达式 - 它们只是被您使用 C# 的查询运算符所隐藏。
Consider that this:
考虑一下：
IEnumerable<int> allChecked = (from item in chkBoxList.Items.Cast<ListItem>()
where item.Selected
select int.Parse(item.Value));
Gets compiled to this:
编译成这样：
IEnumerable<int> allChecked = chkBoxList.Items.Cast<ListItem>()
.Where(i => i.Selected)
.Select(i => int.Parse(i.Value));
As you can see you are already using two lambda expressions (they are the parameters to the Whereand Selectmethods) and you didn't even know it! This query is fine and I wouldn't change it at all.
正如您所看到的，您已经在使用两个 lambda 表达式（它们是Where和Select方法的参数），而您甚至都不知道！这个查询很好，我根本不会改变它。
回答by Jon Skeet
I would improve the query expression by making the call to Cast<T>implicit:
我将通过调用Cast<T>隐式来改进查询表达式：
IEnumerable<int> allChecked = from ListItem item in chkBoxList.Items
where item.Selected
select int.Parse(item.Value);
When you specify the type of a range variable, the compiler inserts a call to Cast<T>for you.
当您指定范围变量的类型时，编译器会Cast<T>为您插入对 的调用。
Other than that, I entirely agree with Andrew.
除此之外，我完全同意安德鲁。
EDIT: For GONeale:
编辑：对于GONeale：
IEnumerable<int> allChecked = chkBoxList.Items
.Cast<ListItem>()
.Where(item => item.Selected)
.Select(item => int.Parse(item.Value));
