C# programatically using a string as object name when instantiating an object

Question

This is a contrived example, but lets say I have declared objects:

CustomObj fooObj;
CustomObj barObj;
CustomObj bazObj;

And I have an string array:

string[] stringarray = new string[] {"foo","bar","baz"};

How can I programatically access and instantiate those objects using the string array, iterating using something like a foreach:

foreach (string i in stringarray) {
    `i`Obj = new CustomObj(i);
}

Hope the idea I'm trying to get across is clear. Is this possible in C#?

Thanks in advance.

Answer 1

You need to be clear in your mind about the difference between an object and a variable. Objects themselves don't have names. Variable names are decided at compile-time. You can't access variables via an execution-time-determined name except via reflection.

It sounds like you really just want a Dictionary<string, CustomObj>:

Dictionary<string, CustomObj> map = new Dictionary<string, CustomObj>();

foreach (string name in stringArray)
{
    map[name] = new CustomObj(name);
}

You can then access the objects using the indexer to the dictionary.

If you're really trying to set the values of variables based on their name at execution time, you'll have to use reflection (see Type.GetField). Note that this won't work for local variables.

Answer 2

You can't.

You can place them into a dictionary:

Dictionary<String, CustomObj> objs = new Dictionary<String, CustomObj>();

foreach (string i in stringarray)
{
    objs[i] = new CustomObj(i);
}

But that's about as good as it gets.

If you store the objects in fields in your class, like this:

public class SomeClass
{
    private CustomObj fooObj;
    private CustomObj barObj;
    private CustomObj bazObj;
}

Then you can reach them through reflection. Let me know if that's the route you want to take.

Answer 3

This is possible using reflection if the variables are class member variables, but it's hideously slow for anything more than very specialized applications. I think if you detail what you're trying to do, we can better offer suggestions. There's very rarely a case where you should access a variable like you're doing.

Answer 4

One option is the totally dynamic route, as per this article, where you specify a code block in a string and then compile/run it from within your program

Answer 5

Another option, less flexible, but simpler is via Activator.CreateInstance - where you ask for a new object to be created - it won't assign to dynamic variables, but is that needed?

Answer 6

I think what he's asking is what i want to do too:

I need to concat some strings based upon the url of the video playing in a media element. Then get the button with the same name and change its state.

in javascrpit you do like this:

var b = "button"; var i = "1"; var name = b + i;

getElementbyID(name).visibility = true;

c# lets me concat the string i need, but i cant get the visualstatemanager to find the object using the value of the string variable.

What am i not getting about C#? I could write dozens of singular functions that all work for each button object, but i'm used to writing a loop that iterates through each element finding the corect one, not knowing the onject i want upfront, which C# seems to want.

any hints?

Answer 7

you can use a find function:

    public static Control FindControl(string controlId, Control container)
    {
        if (container.ID == controlId)
            return container;

        foreach (Control control in container.Controls)
        {
            Control c = FindControl(controlId, control);
            if (c != null)
                return c;
        }
        return null;
    }

and then you will get your control, based on index like this: TextBox firstname = (TextBox) FindControl(string.Concat("TextBox", index.ToString()), this); I hope this helps.

Answer 8

@jotte: Thanks alot for that function. I used it and it works! Except that you need to change container.ID by container.Name

Then you just need to use something like (this example is for checkbox, but any type of variable could work):

string Test = "cbACn" + i.ToString(); CheckBox cbTest = (CheckBox)FindControl(Test, gbACSCAT); if (cbTest != null) { cbTest.Checked = true; }