您需要一个带有构造函数的只读属性，让您为该属性设置值吗？

Question

How is a read-only property with a constructor that lets you set the values:

public class Customer
{
    private int m_id = -1;

    public Customer(int id)
    {
         m_id = id;
    }

    public int ID
    {
        get
        {
            return m_id;
        }
    }
}

different from a normal get, set property like the following?

public class Customer
{
    private int m_id = -1;

    public int ID
    {
        get
        {
            return m_id;
        }
        set
        {
            m_id = value;
        }
    }

Answer 1

The read-only property does not allow other classes within the program to set the property value. The traditional property does.

In this case, the class is forcing the programmer to provide an int ID in the constructor. Having a public property would nearly negate this requirement as the programmer could alter the value of ID at any time.

Answer 2

Members variables set within the object constructor can be declared using the readonly keyword. This allows the variable to act as a constant (eg attempting to change it will generate a compile-time error) but still allow you to set it to a different value for each object instance. This is a bit of syntactic sugar that can help prevent your coders from accidentally modifying values that are not meant to be modified.