名称“__o”在当前上下文中不存在 [英] The name '__o' does not exist in the current context

问题描述

我刚刚安装了Visual Studio 2015并打开了我正在开发的asp .net项目。我收到许多错误（完全相同）如下：

I just installed Visual Studio 2015 and opened my asp .net project that I was working on. I'm receiving many errors (all exactly the same) as below:

错误CS0103当前名称__o不存在上下文

Error CS0103 The name '__o' does not exist in the current context

实际上，我没有任何名为__o的变量，代码的工作方式类似于charm（错误无效）我是我不能看到当我的代码真的有一个错误，因为它在这个列表中的某个地方，我应该检查整个列表。

Well actually I don't have any variables named __o and the code works like a charm (error is invalid) but what bothers me is that I'm not able to see when my code really has a error as it goes somewhere in this list and I should check the whole list.

推荐答案

我发现如果我选择 Build Only 而不是 Build + IntelliSense 的错误（与intellisense相关）将会消失。

I found out that if I choose Build Only instead of Build + IntelliSense the errors (that are related to intellisense) will go away.

更新1：原因

Update 1: The Reason

发生这种情况的原因是这样的代码：

The reason that this is happening is that for codes like this:

<% if (true) { %>
    <%=1%>
<% } %>
<%=2%>

为了在设计时在<％=％>块中提供智能感知，ASP.NET生成赋值给临时的__o变量和语言（VB或C＃），然后提供变量的智能感知。这在页面编译器看到第一个<％= ...％>块时完成。但是这里，块是在if里面，所以后如果关闭，变量超出范围。我们最终生成这样的东西：

In order to provide intellisense in <%= %> blocks at design time, ASP.NET generates assignment to a temporary __o variable and language (VB or C#) then provide the intellisense for the variable. That is done when page compiler sees the first <%= ... %> block. But here, the block is inside the if, so after the if closes, the variable goes out of scope. We end up generating something like this:

if (true) { 
    object @__o;
    @__o = 1;
}
@__o = 2;

解决方法是在页面的早期添加一个虚表达式。例如。 <％=％>。这将不会呈现任何东西，并且它将确保在任何潜在的if（或其他范围界定）语句之前，在Render方法中将__o声明为顶级。

The workaround is to add a dummy expression early in the page. E.g. <%="" %>. This will not render anything, and it will make sure that __o is declared top level in the Render method, before any potential if (or other scoping) statement.

Update 2：摆脱此错误，而不会失去其他intelliSense错误

点击错误列表面板左上角的过滤器按钮， CS0103 ，其中包含错误代码：当前上下文中不存在__o名称，这些错误将不再显示，您仍然可以有其他IntelliSense错误和警告：

Click on the filter button on the top left corner of the error list panel and uncheck the CS0103 which the error code for the: The name '__o' does not exist in the current context and these errors will not be shown anymore and you can still have other intelliSense errors and warnings:

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