Do you know how to create ‘N’ number of instance of class in C#? In my article about the OOP and C# interview question I have asked one of the question (question number 3). Before reading this article you may want to read about the singleton pattern here.
Creating N instance of class
What is the best way to create ‘N’ number of instance of a class. Please check the code below to find the answer.
public class NumberedInstance
{
private static int instanceNumber;
private NumberedInstance()
{
}
public static NumberedInstance GetInstance()
{
if(instanceNumber < 5)
{
instanceNumber++;
return new NumberedInstance();
}
else
{
throw new ArgumentOutOfRangeException("Only five instance of the class are allowed");
}
}
}As you can see in the above C# code I have created a simple class with private constructor. I can access the public static method named GetInstace(), to get the instance. If the number of instances are more then 5 we will get an exception.
In the above class I have created a class with private constructor. And a static field to keep the number of counts of the instances created.If the count exceeds any specified number an exception is thrown.
Create instance of class for each assembly
If I want to extend this example with an instance for each assembly. I have to write the code as shown below
public class NumberedInstance
{
private static IDictionary<string, NumberedInstance> assemblyInstance= new Dictionary<string, NumberedInstance>();
private NumberedInstance()
{
}
public static NumberedInstance GetInstance(string assemblyName)
{
if(!assemblyInstance.Keys.Contains(assemblyName))
{
NumberedInstance instance = new NumberedInstance();
assemblyInstance.Add(new KeyValuePair<string, NumberedInstance>(assemblyName, instance));
return instance;
}
else
{
return assemblyInstance[assemblyName];
}
}
}
In the above code I have used a dictionary to keep records of all the instances created for the assemblies. If the dictionary already contains the instance. The same instance is returned otherwise a new instance is returned and stored in the dictionary.
In this article I have discussed the ways to create the n instance of a class in C#. And their usage examples.