C# 将列表转换为字典

Question

I'm trying to convert a List<Ctrl> to a Dictionary<string, Ctrl> using Ctrl.Name as the key. I've referenced this page to attempt to achieve this: Microsoft's Enumerable.ToDictionary Method page

Hence, my code looks like this:

Dictionary<string, Ctrl> oActionControls;

oActionControls = (from ctrl in _ctrls.Items
                   where ctrl.CtrlTypeCode == "BUTTON"
                   orderby ctrl.TabIndex
                   select ctrl).ToList().ToDictionary<string, Ctrl>(a => a, b => b.Name);

I get an error on ToDictionary<string, Ctrl>(a => a, b => b.Name) which reads: Instance argument: cannot convert from 'System.Collections.Generic.List<AppData.Ctrl>' to 'System.Collections.Generic.IEnumerable'

Argument 3: cannot convert from 'lambda expression' to 'System.Collections.Generic.IEqualityComparer<AppData.Ctrl>'

Argument 2: cannot convert from 'lambda expression' to 'System.Func<string,AppData.Ctrl>'

'System.Collections.Generic.List<AppData.Ctrl>' does not contain a definition for 'ToDictionary' and the best extension method overload 'System.Linq.Enumerable.ToDictionary<TSource,TKey>(System.Collections.Generic.IEnumerable, System.Func<TSource,TKey>, System.Collections.Generic.IEqualityComparer)' has some invalid arguments

Not entirely sure what I'm doing wrong here. Also, it seems strange to me that a Dictionary is declared in the order <key, value> and the ToDictionary constructor takes the lambda functions in the order <value, key> .

How do I fix this? I'm a bit lost. Thanks.

Edit: Added to list, and included all the compiletime errors.

Edit 2: Removed the type arguments for ToDictionary. I've also removed the ToList() call which is superflous, so that the code reads:

oActionControls = (from ctrl in _ctrls.Items
                   where ctrl.CtrlTypeCode == "BUTTON"
                   orderby ctrl.TabIndex
                   select ctrl).ToDictionary(a => a.Name);

which works correctly.

Answer 1

Assuming you have a List<Ctrl> , you could create the dictionary simply by calling .ToDictionary() with a key selector parameter (see MS docs ):

Dictionary<string, Ctrl> actionControls = ctrls.ToDictionary(ctrl => ctrl.Name);

Make sure you have a using System.Linq; statement.

Also - a dictionary does not have an order, so you could remove the order by clause from the query.

Verifyable example:

var ctrls = new List<Ctrl>
{
    new Ctrl { CtrlTypeCode = "1", Name = "My value 1" },
    new Ctrl { CtrlTypeCode = "2", Name = "My value 2" },
    new Ctrl { CtrlTypeCode = "3", Name = "My value 3" },
};
Dictionary<string, Ctrl> actionControls = ctrls.ToDictionary(ctrl => ctrl.Name);

Answer 2

    public class Class2
    {
        public string name;
        public int age;
    }

    List<Class2> list = new List<Class2>();
    Class2 c1 = new Class2();
    c1.name = "Tom";
    c1.age = 15;
    Class2 c2 = new Class2();
    c2.name = "Ada";
    c2.age = 17;
    list.Add(c1);
    list.Add(c2);
    Dictionary<string, Class2> dict = new Dictionary<string, Class2>();
    dict = list.ToDictionary(b => b.name);