String as variable name

Question

is it possible in C# to use a String like a variable name ?
I have got a:

String x = "matrix1_2";
Microsoft.VisualBasic.PowerPacks.RectangleShape y = ???;

??? - there should be the name of variable...matrix1_2

I think you are confusing the name and the value of a variable. Or I'm confused. — kenny, Feb 07 '12 at 20:04
It's *possible* using reflection, but it's not a good idea, usually. What do you want to achieve? There's probably a better way. — Blorgbeard, Feb 07 '12 at 20:06
possible dupe http://stackoverflow.com/questions/4629/c-sharp-eval-equivalent — MikeM, Feb 07 '12 at 20:06

score 14 · Accepted Answer · answered Feb 07 '12 at 20:06

14

No, you can't, and it makes no sense honestly to have a feature like that.

If you need to dynamically assign some data with key and value, you could use an dictionary:

Dictionary<string, RectangleShape> shapes = new Dictionary<string, RectangleShape>();
shapes.Add("matrix1_2", new RectangleShape( ... ));

Then you can simply read the "variable" like

shapes["matrix1_2"]

answered Feb 07 '12 at 20:06

Denis Biondic

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Got it...I love you!...t need this!...Thanks so much! – hradecek Feb 07 '12 at 20:14
@hradecek If you feel your question has been answered you can "accept" it by clicking on the check sign to the left of the answer. – ispiro Feb 07 '12 at 20:57

score 2 · Answer 2 · answered Feb 07 '12 at 20:05

2

This is not possible.

You can't have dynamic variable names in C#, VB.NET or any .NET language. There is no support for such a feature.

answered Feb 07 '12 at 20:05

Oded

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Roslyn supports variable access like this, but other than that, this is correct. – McKay Feb 07 '12 at 20:06
@McKay - Roslyn is a very different matter. It is **not** C#. – Oded Feb 07 '12 at 20:07
@Oded, it's certainly not the best way to do it I don't think but if he knows what assembly the variable resides in he ought to be able to use reflection, right? – Brandon Moore Feb 07 '12 at 20:08
@BrandonMoore - reflection is not the same as declaring a variable name in runtime. – Oded Feb 07 '12 at 20:08
@Oded Roslyn is a different matter, but it is available in C# (CTP) – McKay Feb 07 '12 at 20:08
1

@Oded I didn't think he wanted to declare variable at runtime, but just access them by name at runtime. Maybe I'm misunderstanding the question though... – Brandon Moore Feb 07 '12 at 20:11
@Oded Right, that would solve his problem were it possible. It looks like what is actually has right now though is a variable that holds variable names... so maybe reflection is a possibility though it would require a workaround to account for the fact that reflection doesn't access method variables (as StriplingWarrior just pointed out on my answer). – Brandon Moore Feb 07 '12 at 20:17
1

@BrandonMoore - He probably just needs a collection but doesn't know how to express that. – Oded Feb 07 '12 at 20:18

score 2 · Answer 3 · answered Feb 07 '12 at 20:06

No it is not. If "matrix1_2" is a local variable, then you can't do it as the variable might not even exist after the compiler is through, if it is actually an instance field, then reflection may help:

object value = obj.GetType().GetField(fieldName).GetValue(obj);

score 0 · Answer 4 · answered Jan 24 '14 at 06:29

You can get a field value from a dynamic type in this manner (using C# in a Silverlight 5 project).

Type itemType = item.GetType();
try
{
    PropertyInfo field = itemType.GetProperty(fieldName);
    object val = field.GetValue(item, null);
}
catch (Exception ex)
{
    // field doesn't exist, do something else
}

*Where "item" is a dynamic type generated at runtime (but doesn't have to be) and "fieldName" is a string for the property name you are looking for.

score 0 · Answer 5 · answered Feb 07 '12 at 20:06

0

Seems like a bad idea. Try with enums or own datatypes /classes

answered Feb 07 '12 at 20:06

chrs

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Brandon Moore · Answer 6 · 2012-02-07T20:24:51.447

0

You could with reflection, but I suspect in this case theere is a better design you could implement that would be better than using reflection. If you provide a little more info probably one of us could help you with that.

Declare a dictionary variable:

Dictionary<string, RectangleShape> rectangleDictionary = new Dictionary<string, RectangleShape>();

Then, where you would normallay write "matrix1_2 = somevalue;", instead write:

rectangleDictionary.add("matrix1_2", somevalue)

Then you'll be able to work with the variable name:

rectangleDictionary["matrix1_2"] = someothervalue;
rectangleDictionary["matrix1_2"].someproperty = something;

Microsoft.VisualBasic.PowerPacks.RectangleShape y = rectangleDictionary["matrix1_2"];

edited Feb 07 '12 at 20:24

answered Feb 07 '12 at 20:06

Brandon Moore

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Probably there is a way to do what you want by using a Dictionary<> object to store the keys and values in. – Brandon Moore Feb 07 '12 at 20:08
Reflection does not allow access to variables within a method: only methods, fields, types, and properties. – StriplingWarrior Feb 07 '12 at 20:08
@StriplingWarrior That certainly does complicate the matter, though that could probably be worked around... definitely not worth working around though as I'm sure there are better options for his problem. – Brandon Moore Feb 07 '12 at 20:19

score 0 · Answer 7 · answered Feb 07 '12 at 20:36

0

Does "matrix1_2" exist already? In other words, when you say y = ??? are you trying to access an existing variable or create one.

To my knowledge, there is no way to create a new "named" instance at run-time. However, you can retrieve the names of existing fields and select them using System.Reflection.

String x = "matrix1_2";
Microsoft.VisualBasic.PowerPacks.RectangleShape y;
Type type = typeof(MyType); // Get type pointer
FieldInfo[] fields = type.GetFields();
foreach (var field in fields)
{
        if (field.Name == "matrix1_2")
        {
            y = field;
        }
}

MyType above is the name of whatever class matrix1_2 lives in.

answered Feb 07 '12 at 20:36

Justin

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What if matrix1_2 isn't in a class, it's just a variable in the method? – McKay Feb 07 '12 at 20:47
@McKay - I do not believe that variable names are preserved inside a method. Once you compile down to CIL bytecode they are referenced by position (eg. V_0, V_1, V_2, etc) and whatever name you gave them is lost. So, even if you were able to dynamically create a new local variable, it would take some deep magic to refer to it in your C# programs. You might be able to use [AOP](http://en.wikipedia.org/wiki/Aspect-oriented_programming) (perhaps with [PostSharp](http://www.sharpcrafters.com/) – Justin Feb 20 '12 at 18:34
That is precisely my point. He wants to access a theoretically arbitrary variable. If it's a field, this code will work, if it's a property, other code will work, if it's a parameter, other code could work. You don't have a very generalized solution. – McKay Feb 21 '12 at 14:50

score -1 · Answer 8 · edited Jan 07 '22 at 19:59

-1

You can use a string in Control.Find function like below statement.

ComboBox comboBoxElement  = (ComboBox)this.Controls.Find("comboBoxNameThatYouSearch", true)[0];

edited Jan 07 '22 at 19:59

Paul Roub

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answered Jan 07 '22 at 19:53

erdemu

1

Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Jan 07 '22 at 20:34

String as variable name

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