什么是c＃/ VB.net的Benifit / Advantage优势属性 - Setters的私有访问修饰符

Question

Below is the class with a property.

public class abc
    {
        public int MyProperty { get; private set; }
    }

Confusion - What's the benefit of typing private access modifier in setter ?

Answer 1

Simply, it's a property that the class itself is allowed to set, but external objects can only read. Perhaps MyProperty changes as a side effect to a method, perhaps it is only set once (in a constructor). The main point is the source of change with MyProperty has to come from within abc (or a nested class of abc ), not from something outside that holds a reference to it.

As for why you might use it, perhaps outside code cannot be trusted to set this value. The class isn't strictly immutable , it can change, but the only code trusted to do it exists inside the class (or a nested class). The outside world can simply read.

Answer 2

private修饰符允许属性在公共，受保护或内部访问的上下文中是只读的，同时赋予类型本身设置属性的能力（即，在私有访问的上下文中）。

Answer 3

There are a couple reasons to use private set.

1) If you are not using a backing field at all and want a read-only automatic property:

public class abc
    {
        public int MyProperty { get; private set; }
    }

2) If you want to do extra work when you modify the variable inside your class and want to capture that in a single location:

private string _name = string.Empty;
public string Name 
{ 
    get { return _name; }
    private set 
    {
        TextInfo txtInfo = Thread.CurrentThread.CurrentCulture.TextInfo;
        _name = txtInfo.ToTitleCase(value);
    }
}

In general, though, it's a matter of personal preference. Far as I know, there are no performance reasons to use one over the other.

Answer 4

This is done to make your property read-only so that the external world is not allowed to change the value of the property and only the class implementing the property can change the property value being the owner of the property. As an example of how a class tracks its instance count and the instance count only can be increased/decreased from inside the class and the external world should not be allowed to change the instance count property eg:

public class Customer
{    
    public Customer()
    {
        InstanceCount++;
    }

    //Helps retrieving the total number of Customers
    public int InstanceCount { get; private set; } //Count should not be increased by the clients of this class rather should be increased in the constructor only
}

Another benefit in some situations is, after giving a private set to your property you can give a Set method for changing the property value from external world when you want to do some calculations or validations on the value received (which is not a best practice to do inside the Set property accessors), and then change the value of the property as follows:

public class Customer
{
    public string City { get; private set; }

    public bool SetCity(string customerCity)
    {
        //validate that the customerCity is a valid USA city or else throw some business rule exception, and then call below code
        City = customerCity
    }
}

Answer 5

私有setter允许只在内部设置属性，而getter仍公开公开属性值。