非常简单的C＃程序生成一个`NullReferenceException是未处理的'错误 [英] Very simple C# program generates a `NullReferenceException was unhandled` error

问题描述

我有一个简单的WinForm，我用来尝试帮助我与ADO.NET。
它有一个datagridview

I have a simple WinForm that I'm using to try to help me with ADO.NET. It has a datagridview

我添加了一个紧凑的sql服务器数据库到项目 experiment.sdf

I have added a compact sql server database to the project called experiment.sdf

在App.config文件中我添加了以下内容。我使用一个以前的项目应用程序文件，以此为基础，所以也许这里有一个错误：

In the App.config file I have added the following. I used a previous project app file to base this on so maybe there's an error in here?:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<configSections>
</configSections>
<connectionStrings>
  <add name="DatabaseDGVexperiments.Properties.Settings.DatabaseDGVexperimentsConnStg"
      connectionString="Data Source=|DataDirectory|\experiment.sdf"
      providerName="Microsoft.SqlServerCe.Client.3.5" />
</connectionStrings>
</configuration>

我已经添加了对配置库的引用。

I've added a reference to the configuration library.

后面的代码如下：

  SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["DatabaseDGVexperimentsConnStg"].ConnectionString);

当它命中行 SqlConnection conn = ... 我得到一个错误 NullReferenceException未处理。如何解决此问题？

When it hits the line SqlConnection conn = ... I get an error NullReferenceException was unhandled. How do I fix this?

推荐答案

更改：

name="DatabaseDGVexperiments.Properties.Settings.DatabaseDGVexperimentsConnStg"

name="DatabaseDGVexperimentsConnStg"

或更改：

ConfigurationManager.ConnectionStrings["DatabaseDGVexperimentsConnStg"]

到：

ConfigurationManager.ConnectionStrings["DatabaseDGVexperiments.Properties.Settings.DatabaseDGVexperimentsConnStg"]

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