Dynamic allocation of Object type

Mark

Dear All,

I have a program which can read Data from more than one type of source - i.e. a File or XML feed. I have a listview with a list of sources and the source to retrieve from.

Is it possible to assign the type of object created without using an IF statement?

Here is some code detail. I have an Interface (IData) which has a method ReadData. Two classes - XMLData and CSVFileData implement this interface.

Then in a click button event on my Form I have:

Type t = typeof(CSVFileData);

messageQueue = Control.LoadData(t, listViewDataSource.SelectedItems[0].SubItems[1].Text);

This sends the Type t, and source path (either filename or url) into the static control class.

In the Control.LoadData method I run:

object o = Activator.CreateInstance(TypeObj);

//check that it implements the IData Interface

IData dataReader = o as IData;

if (dataReader != null)

{

messages = dataReader.ReadData(Source);

}

I have everything in place to do everything dynamically. The only thing that I would like to get rid of is the need to say:

(pseudocode)

if (listboxValue="CSV") {

Type t = typeof(CSVFileData);

} else {

Type t = typeof(XMLData);

}

How can I assign the Type (CSVFileData) more dynamically?

I thought about adding an extra field to the listview to hold the Type, but I'm not sure how you'd convert the string literal to a type.

I am very new to C# so I hope the above makes sense. Any help/pointers would be greatly appreciated!

6 Replies

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Alan19y ago
This is the overload I'm talking about:

http://msdn2.microsoft.com/en-us/library/w3f99sx1.aspx

It works fine as long as you pass it a string which contains the fully qualified name of a type.
Mark19y ago
Ahh, no what I mean is that there doesn't seem to be an overload for Type that accepts a parameter as in your example:

Type t = Type.GetType(listboxValue);

I can only get it to work with an object instance, ie:

Object obj = new Object();

MessageBox.Show(obj.GetType().ToString());

which returns System.Object as you'd expect.

Did you mean that I would be able to convert the string value held in the listview to a type to be used by:

Activator.CreateInstance(Type);

and if so, how do I do it. That is what I want to achieve as I don't have an object instance until runtime (ie. I don't know which data source the user will select). Sorry for the confusion!

Thanks

Andrew
Alan19y ago
It is in fact a static method of the Type class, Andrew, and so you don't need an instance to use it :)
Mark19y ago
When I try to do this, there doesn't appear to be an overload for GetType that takes an argument in the way you showed. It needs an instance of an object before it will return a type, which is no good as I don't have an object instance yet. All I get back if I try to get the Type of the Text property of the ListView SubItem is System.String.

Have I misunderstood how this works or the way I should be using it?

Many Thanks
Andrew
Mark19y ago
Thanks very much for the help Alan, I will give it a try!
Alan19y ago
Well, you could replace the 'if' statement with

Type t = Type.GetType(listboxValue);

where listboxValue contains the name of the type as a string. However, the problem here is that you have to supply it with the fully qualified name of the type or else it won't work:

http://msdn2.microsoft.com/en-us/library/w3f99sx1.aspx

You'd therefore need to save the fully qualified name to the ListBox or code a method which mapped an abbreviated name to the fully qualified name and then use that:

Type t = Type.GetType(GetFullName(listboxValue));