c# 对象 obj 的值为 {}.什么是“{}"? [英] c# Object obj's value is {}. What is "{}"?

问题描述

我正在使用一些运行 sql 查询的旧代码作为参考.

I'm using some old code that runs a sql query as a reference.

在某些时候，它会变成这样:

At some point, it gets to something like:

sqlDataAdapter.Fill(dataSet);
DataRow dataRow = dataSet.Tables[0].Rows[0];
Object obj = dataRow[fieldName];

旧代码:

string output;
if (!string.IsNullOrEmpty(obj.ToString())) { output = obj.ToString(); }
else { output = "Not Available"; }

我将它们更改为:

output = obj as string ?? "Not Available"

但有时，它坏了.正如我怀疑的那样，当条目是 int 时，它正在发生中断.在这些情况下转换为 int 解决了这个问题.

But sometimes, it broke. As I suspected, it was happening breaking when the entry was an int. Casting as an int in those cases solved that problem.

然后当obj[fieldName] 类型为int 的没有 条目时出现了另一个问题.当我逐步调试调试器时，我惊讶地发现 obj 不是 null.在 VS 中，鼠标悬停显示它有一个值 {}.

Then another problem arose when there was no entry for obj[fieldName] of type int. When I stepped through the debugger, I was surprised to find that obj wasn't null. In VS, mousing over revealed it had a value {}.

{} 到底是什么?我如何对其进行布尔测试?

What the heck is {}? How do I make a boolean test of it?

(在旧代码中，它出现 .ToString() 在这种情况下返回 "" 并按预期工作.)

(In the old code, it appears .ToString() returns "" in this case and works as expected.)

推荐答案

{ 和 } 是左括号和右括号，是对象开始和结束的符号.因此，一个没有特殊属性的空对象被简写为 {}.调试器使用这种表示法来帮助您直观地区分空对象、空字符串和 null.

{ and } are opening and closing braces and symbolic of the start and finish of an object. Hence an empty object with no special properties is depicted in shorthand as {}. The debugger uses this notation to help you visually distinguish between an empty object, an empty string and null.

如果您将鼠标悬停在 obj[fieldName] 上并且没有 fieldName 的条目，则调试器不会关心它，它会显示 <代码>对象.您必须使用立即窗口或手表/快速手表.调试器只会看到您将鼠标悬停在 obj 上，并假设您指的是数组本身，而不是指定索引处的数组内容.

If you hover over obj[fieldName] and there is no entry for fieldName, the debugger won't care about that, it'll show the value of obj. You'll have to use the immediate window or a watch/quickwatch. The debugger will only see you hovering over obj and assume you're referring to the array itself, not the contents of the array at the specified index.

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