c# | get/set变量总是返回null

Question

这是public static类中的代码:

public static string _json { get; set; }
public static string Json
{
get { return _json; }
set { 
_json = Json;
Console.WriteLine("Json variable was modified. Now it's value is: " + _json);
}
}

为什么设置Json = "{}";会导致NullReference异常?

Answer 1

_json = Json;将再次调用getter，返回(旧的)后台字段值。所以你当前的代码类似于这样:

public static string get_Json() => _json;
public void set_Json(string value) => 
{
var newValue = get_Json(); // here _json just returns the old value
// you don´t use the provided value here
_json = newValue; 
}

您需要使用value-关键字:

public static string Json
{
get { return _json; }
set { 
_json = value;
Console.WriteLine("Json variable was modified. Now it's value is: " + _json);
}
}

Answer 2

Setter应该分配"value"变量，如

set {
json = value;
Console.Write...
}