在 C# 中使用“对象”数据类型，它是否包含成员？

Question

I am a little confused as to the use of the keyword "object" using in C#. What can and can't it be used for. Can you access a member?

For example, I have made a small snippet of code to deserialize a JSON string.

public static object DeserializeString(string jsonstring)
{
    // Deserialize the data
    object testObject = JsonConvert.DeserializeObject<object>(jsonstring);
    return testObject;
}

When I use the deserializer to create an object I can not access any memebers. I know that this may be a silly question because I haven't defined a class with any members to want to access it. I am trying to avoid making dozens of classes.

Thanks in advance!

Answer 1

I am a little confused as to the use of the keyword "object" using in C#. What can and can't it be used for. Can you access a member?

C# is by default a statically typed language . That is, if you have an expression of a particular compile-time type you may access only the members of that type. This is a safety system; it is saying "I only have a guarantee that the members of this type are available, so prevent me from accessing any other members".

If you have an expression of type object then you may access the members of object -- ToString , GetType and so on.

If you want to turn off this safety system, use dynamic instead of object , and you can then call any member you like; if you call a member that does not exist, your program will crash. When you turn off a safety system the safety system is turned off and you become responsible for guaranteeing safety .

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CLARIFICATION: Commenter Brian correctly points out that in the specific case of JSON objects, the default behaviour of a bad dynamic member access is to produce null rather than crashing; of course, much of the time after producing null because a member is unexpectedly missing, the next thing that will happen is a null dereference crash, so there's actually not a whole lot of additional safety margin there, but there is at least some.

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My question to you was:

If you call GetType().ToString() on the object, what do you get?

The answer was Newtonsoft.Json.Linq.JObject . So in this case you can access the members of that type like this:

JObject jo = (JObject)testObject;

(Assuming you have using Newtonsoft.Json.Linq; in your directives.)

Again, your program will crash if the object is not actually of that type.

You can do a safe type test with:

if (testObject is JObject jo)
{
  var r = jo.Root;
  ...

I am trying to avoid making dozens of classes.

C# is a statically-typed language; it encourages creation of classes. Again, this is a safety system. Invest in its correct usage!