Why doesn't initializer work with properties returning list?

问题

Couldn't find an answer to this question. It must be obvious, but still.

I try to use initializer in this simplified example:

    MyNode newNode = new MyNode 
    {
        NodeName = "newNode",
        Children.Add(/*smth*/) // mistake is here
    };

where Children is a property for this class, which returns a list. And here I come across a mistake, which goes like 'Invalid initializer member declarator'.

What is wrong here, and how do you initialize such properties? Thanks a lot in advance!

回答1:

You can't call methods like that in object initializers - you can only set properties or fields, rather than call methods. However in this case you probably can still use object and collection initializer syntax:

MyNode newNode = new MyNode
{
    NodeName = "newNode",
    Children = { /* values */ }
};

Note that this won't try to assign a new value to Children, it will call Children.Add(...), like this:

var tmp = new MyNode();
tmp.NodeName = "newNode":
tmp.Children.Add(value1);
tmp.Children.Add(value2);
...
MyNode newNode = tmp;

回答2:

It is because the children property is not initialized

MyNode newNode = new MyNode 
    {
        NodeName = "newNode",
        Children = new List<T> (/*smth*/)
    };

回答3:

Because you're executing a method, not assigning a value

回答4:

The field initializer syntax can only be used for setting fields and properties, not for calling methods. If Children is List<T>, you might be able to accomplish it this way, by also including the list initializer syntax:

T myT = /* smth */

MyNode newNode = new MyNode 
{
    NodeName = "newNode",
    Children = new List<T> { myT }
};

回答5:

The following is not setting a value in the initialiser:

Children.Add(/*smth*/) // mistake is here

It's trying to access a member of a field (a not-yet-initialised one, too.)

回答6:

Initializers is just to initialize the properties, not other actions.

You are not trying to initialize the Children list, you are trying to add something to it.

Children = new List<smth>() is initializing it.

来源：https://stackoverflow.com/questions/6385803/why-doesnt-initializer-work-with-properties-returning-listt

标签

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initializer

Why doesn't initializer work with properties returning list<t>?