我刚刚在Jeffrey Richter的书(CLR通过C#4.0,第257页)发现我的代码,并误解了为什么它的工作原理.
public sealed class Classroom
{
private List<String> m_students = new List<String>();
public List<String> Students { get { return m_students; } }
public Classroom() { }
}
class Program
{
static void Main(string[] args)
{
Classroom classroom = new Classroom {
Students = { "Jeff","Kristin" }
};
foreach (var student in classroom.Students)
Console.WriteLine(student);
}
}
结果：
Jeff Kristin
正如你所看到的,我们有一个名为“学生”的访问器属性,它只有getter(不是setter！),而是在’Main’函数中,当我们要初始化’classroom’变量时,我们初始化’Students’字段“课堂”类型：
Classroom classroom = new Classroom {
Students = { "Jeff","Kristin" }
};
我一直以为,当表达式(int i = 1)的“左侧”中的变量,然后编译器应该访问setter函数,并且在“right-side”(int x = i 2)到getter函数时.
为什么在杰弗里的代码中这么有趣的行为(可能只是对我来说,对不起,如果是这样).
解决方法
从C#5规范的7.6.10.2部分：
A member initializer that specifies a collection initializer after the equals sign is an initialization of an embedded collection. Instead of assigning a new collection to the field or property,the elements given in the initializer are added to the collection referenced by the field or property. The field or property must be of a collection type that satisfies the requirements specified in §7.6.10.3.
所以这段代码：
Classroom classroom = new Classroom {
Students = { "Jeff","Kristin" }
};
相当于：
Classroom tmp = new Classroom();
tmp.Students.Add("Jeff");
tmp.Students.Add("Kristin");
Classroom classroom = tmp;
基本上,对象初始化器中的=与独立赋值语句不完全相同.
编辑：这段代码
Classroom classroom = new Classroom {
Students = new List<string> { "Jeff","Kristin" }
};
将无法编译,因为这将尝试为学生调用setter.
