String to a Class name

Hi,

I've got some classes to access different types of databases and I have a string variable that define the type of db I want to access. What I want to do if is pssible use the value of this variable to access the class. I have the following code now.

 switch (dbType)
 {
 case "MSSQL": return MSSQL.msSQLDataSet(sqlString);
 case "ACCESS": return ACCESS.msSQLDataSet(sqlString);
 case "ORACLE": return ORACLE.msSQLDataSet(sqlString);
 case "MYSQL": return MYSQL.msSQLDataSet(sqlString);
 default: return null;
 }

I want to do something like

 SomekindOfTransformation(dbType).msSQLDataSet(sqlString)

instead of using theswitch statement

Thanks,Hi Arty,

You can achieve it using Object.GetType and Type.InvokeMember. VisitObject.GetType andType.InvokeMember for complete details.

Here is a sample code:

using System;
using System.Reflection;
// This sample class has a field, constructor, method, and property.
class MyType
{
 Int32 myField;
 public MyType(ref Int32 x) {x *= 5;}
 public override String ToString() {return myField.ToString();}
 public Int32 MyProp
 {
 get {return myField;}
 set
 {
 if (value < 1)
 throw new ArgumentOutOfRangeException("value", value, "value must be > 0");
 myField = value;
 }
 }
}
class MyApp
{
 static void Main()
 {
 Type t = typeof(MyType);
 // Create an instance of a type.
 Object[] args = new Object[] {8};
 Console.WriteLine("The value of x before the constructor is called is {0}.", args[0]);
 Object obj = t.InvokeMember(null,
 BindingFlags.DeclaredOnly |
 BindingFlags.Public | BindingFlags.NonPublic |
 BindingFlags.Instance | BindingFlags.CreateInstance, null, null, args);
 Console.WriteLine("Type: " + obj.GetType().ToString());
 Console.WriteLine("The value of x after the constructor returns is {0}.", args[0]);
 // Read and write to a field.
 t.InvokeMember("myField",
 BindingFlags.DeclaredOnly |
 BindingFlags.Public | BindingFlags.NonPublic |
 BindingFlags.Instance | BindingFlags.SetField, null, obj, new Object[] {5});
 Int32 v = (Int32) t.InvokeMember("myField",
 BindingFlags.DeclaredOnly |
 BindingFlags.Public | BindingFlags.NonPublic |
 BindingFlags.Instance | BindingFlags.GetField, null, obj, null);
 Console.WriteLine("myField: " + v);
 // Call a method.
 String s = (String) t.InvokeMember("ToString",
 BindingFlags.DeclaredOnly |
 BindingFlags.Public | BindingFlags.NonPublic |
 BindingFlags.Instance | BindingFlags.InvokeMethod, null, obj, null);
 Console.WriteLine("ToString: " + s);
 // Read and write a property. First, attempt to assign an
 // invalid value; then assign a valid value; finally, get
 // the value.
 try
 {
 // Assign the value zero to MyProp. The Property Set
 // throws an exception, because zero is an invalid value.
 // InvokeMember catches the exception, and throws
 // TargetInvocationException. To discover the real cause
 // you must catch TargetInvocationException and examine
 // the inner exception.
 t.InvokeMember("MyProp",
 BindingFlags.DeclaredOnly |
 BindingFlags.Public | BindingFlags.NonPublic |
 BindingFlags.Instance | BindingFlags.SetProperty, null, obj, new Object[] {0});
 }
 catch (TargetInvocationException e)
 {
 // If the property assignment failed for some unexpected
 // reason, rethrow the TargetInvocationException.
 if (e.InnerException.GetType() !=
 typeof(ArgumentOutOfRangeException))
 throw;
 Console.WriteLine("An invalid value was assigned to MyProp.");
 }
 t.InvokeMember("MyProp",
 BindingFlags.DeclaredOnly |
 BindingFlags.Public | BindingFlags.NonPublic |
 BindingFlags.Instance | BindingFlags.SetProperty, null, obj, new Object[] {2});
 v = (Int32) t.InvokeMember("MyProp",
 BindingFlags.DeclaredOnly |
 BindingFlags.Public | BindingFlags.NonPublic |
 BindingFlags.Instance | BindingFlags.GetProperty, null, obj, null);
 Console.WriteLine("MyProp: " + v);
 }
}

Hope this helps,
Appan
Thank you Appana, that helped me a lot.

Structure vs class

in vb.net you can define a structure...what exactly is this, why would I want to use it and what is the advantage as opposed to a class?

Thanks!

Hi,

structure is a value type, while a class is a reference type. Types that developers use most often are value types (such as Integer), while most types in .NET Framework Base Class Library are reference types (classes)

Difference is that reference type is allocated from the managed heap (New operator you use to instantiate it returns the memory address of the object, this is what happens under the covers).E.g with reference types you are given a reference to the object on the managed heap. And reference types are subject to garbage collection.

Value types on the other hand are allocated on thread's stack, it has no pointer to instance, the variable is the instance itself. Therefore value types are lighter for the CLR than reference types (value types are not GC'd). But they also have limitations, and in scenarios where they are needed to treat like an object (which causes boxing and unboxing), they can also cause performance overhead.

Here's also a quick list to see their differences:
http://msdn2.microsoft.com/en-US/library/2hkbth2a(VS.80).aspx