C# – How to get value from the object but its type is unreachable

creflection

For instance, in my current class, there is a hashtable,

Hashtable t = GetHashable(); //get from somewhere.

var b = t["key"];

the type of b is hidden from my current class, it is unreachable, not a public class type.

but i want to get a value from b, for example b has a field call "ID",
i need to get the ID from b.

is there anyway i can get it, reflection ???

Best Answer

If you don't know the type, then you'll need reflection:

object b = t["key"];
Type typeB = b.GetType();

// If ID is a property
object value = typeB.GetProperty("ID").GetValue(b, null);

// If ID is a field
object value = typeB.GetField("ID").GetValue(b);

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Use LINQ:

Dictionary<string, int> myDict = new Dictionary<string, int>();
myDict.Add("one", 1);
myDict.Add("four", 4);
myDict.Add("two", 2);
myDict.Add("three", 3);

var sortedDict = from entry in myDict orderby entry.Value ascending select entry;

This would also allow for great flexibility in that you can select the top 10, 20 10%, etc. Or if you are using your word frequency index for type-ahead, you could also include StartsWith clause as well.

C# – How to get the index of the current iteration of a foreach loop

Ian Mercer posted a similar solution as this on Phil Haack's blog:

foreach (var item in Model.Select((value, i) => new { i, value }))
{
    var value = item.value;
    var index = item.i;
}

This gets you the item (item.value) and its index (item.i) by using this overload of LINQ's Select:

the second parameter of the function [inside Select] represents the index of the source element.

The new { i, value } is creating a new anonymous object.

Heap allocations can be avoided by using ValueTuple if you're using C# 7.0 or later:

foreach (var item in Model.Select((value, i) => ( value, i )))
{
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}

You can also eliminate the item. by using automatic destructuring:

<ol>
foreach ((MyType value, Int32 i) in Model.Select((value, i) => ( value, i )))
{
    <li id="item_@i">@value</li>
}
</ol>

Best Answer

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