为什么初始化程序不能处理返回列表的属性<t> ?

Question

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!

Answer 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;

Answer 2

It is because the children property is not initialized

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

Answer 3

因为你正在执行一个方法，而不是赋值

Answer 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 }
};

Answer 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.)

Answer 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.