Code Contracts 关于方法Contract.Requires<T>()

class Program
{
static void Main(string[] args)
{
A a = new A();
try
{
a.PutA(Console.ReadLine());
}
catch (Exception e)
{
Console.WriteLine(e);
}
}
}

[ContractClass(typeof(AContract))]
public interface IA
{
int ErrorInt { get; set; }
void PutA(string str);
}

[ContractClassFor(typeof(IA))]
sealed class AContract:IA
{
public int ErrorInt { get; set; }

public void PutA(string str)
{
//Console.WriteLine(nameof(AContract));
Contract.Requires<ArgumentNullException>(!String.IsNullOrEmpty(str),"str");
//Contract.Requires(str != null);
//Contract.Ensures(str!=null);
//Contract.EnsuresOnThrow<ArgumentNullException>(str == null);
//Contract.Requires<ArgumentNullException>(ErrorInt == 0,nameof(ErrorInt));
}
}

a.PutA(Console.ReadLine());