Getter without body, Setter with

问题:

I have a property which is currently automatic.

public string MyProperty { get; set; }

However, I now need it to perform some action every time it changes, so I want to add logic to the setter. So I want to do something like:

public string MyProperty {
    get;
    set { PerformSomeAction(); }
}

However, this doesn't build... MyProperty.get' must declare a body because it is not marked abstract, extern, or partial

I can't just have the getter return MyProperty as it will cause an infinite loop.

Is there a way of doing this, or do I have to declare a private variable to refer to? I'd rather not as MyProperty is used through out the code both in this class and outside it

回答1:

You need to use a property with backing field:

private string mMyProperty;
public string MyProperty
{
    get { return mMyProperty; }
    set
    {
        mMyProperty = value;
        PerformSomeAction();
    }
}

回答2:

You can´t implement one without the other, as when using the one it refers to a (hidden) backing-field which is auto-generated in the case of an autogenerated property. However when you implement one you have to set this backing-field in both ways.

The auto-way is just a shortcut for this:

private string _property;
public string MyProperty
{
    get { return _property; }
    set { _property = value; }
}

So if you´d omit the hidden field in one of the methods (this is what getters and setters are actually) how should this method know how to store/get the value?

回答3:

You need to either provide a body for both the getter and setter, or neither.

So if you define either one, it's no longer an auto property.

So you have to do:

Either

public string MyProperty {
    get;
    set;
}// Automatic property, no implementation

OR

public string MyProperty
{
    get { return mMyProperty; }
    set
    {
        mMyProperty = value;
        PerformSomeAction();
    }
}

回答4:

If you are doing something in the setter then you will have to explicitly declare the variable. E.g.

private string _myProperty;
public string MyProperty {
    get { return _myProperty; };
    set 
    {
        _myProperty = value; 
        PerformSomeAction(); 
    }
}

or - in the setter you can pass value to the function and do what you want to it there... assuming you want to change/check the value in the function PerformSomeAction()

回答5:

This is similar to the question C# getter and setter shorthand.

When you manually specify a setter, it won't use the automatic property mechanism for the getter, which is why the error message acts like it's missing. You'll need to write your own getter when you specify the setter.