C# Language Code Contracts Defining Contracts on Interface
Example
[ContractClass(typeof(ValidationContract))]
interface IValidation
{
string CustomerID{get;set;}
string Password{get;set;}
}
[ContractClassFor(typeof(IValidation))]
sealed class ValidationContract:IValidation
{
string IValidation.CustomerID
{
[Pure]
get
{
return Contract.Result<string>();
}
set
{
Contract.Requires<ArgumentNullException>(!string.IsNullOrEmpty(value), "Customer ID cannot be null!!");
}
}
string IValidation.Password
{
[Pure]
get
{
return Contract.Result<string>();
}
set
{
Contract.Requires<ArgumentNullException>(!string.IsNullOrEmpty(value), "Password cannot be null!!");
}
}
}
class Validation:IValidation
{
public string GetCustomerPassword(string customerID)
{
Contract.Requires(!string.IsNullOrEmpty(customerID),"Customer ID cannot be Null");
Contract.Requires<ArgumentNullException>(!string.IsNullOrEmpty(customerID), "Exception!!");
Contract.Ensures(Contract.Result<string>() != null);
string password="AAA@1234";
if (customerID!=null)
{
return password;
}
else
{
return null;
}
}
private string m_custID, m_PWD;
public string CustomerID
{
get
{
return m_custID;
}
set
{
m_custID = value;
}
}
public string Password
{
get
{
return m_PWD;
}
set
{
m_PWD = value;
}
}
}
In the above code, we have defined an interface called IValidation with an attribute [ContractClass]. This attribute takes an address of a class where we have implemented a contract for an Interface. The class ValidationContract makes use of properties defined in the interface and checks for the null values using Contract.Requires<T>. T is an exception class.
We have also marked the get accessor with an attribute [Pure]. The pure attribute ensures that the method or a property does not change the instance state of a class in which IValidation interface is implemented.
