UserControl中的ConfigurationManager连接字符串为null

本文介绍了UserControl中的ConfigurationManager连接字符串为null的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我有一个通过使用像这样一个数据层中获取数据的表格应用程序：

公开数据表的get（查询字符串，ArrayList的参数= NULL） {使用（iDB2Connection CN =新iDB2Connection（ConfigurationManager.ConnectionStrings [i系列]。的ToString（））） { //获取数据并返回它们} }

我有拿到形式数据和这工作得很好。

不过，我创建了一个用户控件它通过这种方法，当我跑我的项目，但其中包含的用户控件的形式，工作正常获取数据。抛出一个设计师异常

为了防止加载设计之前可能的数据丢失，以下错误的必须解决：

我发现错误位于从连接字符串的检索<的appSettings> 。

它抛出一个NullPointerException异常。

但只有在设计模式。当我不理它，一切工作正常，但是，我想知道如何解决这个

为什么我的<的appSettings> 空访问他们时，通过我的用户？

更新1

看来我的用户无法识别<的appSettings方式> 所有

当我把这段代码在我的用户Load事件，我得到一个nullreference为好。

私人无效SelectUser_Load（对象发件人，EventArgs五） { txtLocation.Text = ConfigurationManager.AppSettings [所在地]的ToString（）。 }

解决方案

我找到了解决办法，在的designMode用户控件已经执行中的Load事件的代码。 ，因为在app.config不使用的designMode它没有找到，因此无法加载。 所以我做了它周围的一个小检查，检查中的designMode与否：

布尔的designMode =（LicenseManager有。 UsageMode == LicenseUsageMode.Designtime）; 如果（的designMode） {线位置= ConfigurationManager.AppSettings [所在地]的ToString（）。 }

I have an application which gets data to the forms through a datalayer which uses something like this:

public DataTable get(String query, ArrayList parameters = null) { using (iDB2Connection cn = new iDB2Connection(ConfigurationManager.ConnectionStrings["iseries"].ToString())) { // get the data and return them } }

I have forms which get data and this works fine.

However, I created a UserControl which gets data through this method which works fine when I run my project, however, the form which contains the UserControl throws a designer exception.

"To prevent possible data loss before loading the designer, the following errors must be resolved: "

I found that the error is located at the retrieval of the connection string from the <appSettings>.

It throws a nullpointerexception.

But only in design mode. When I ignore it, everything works fine, however, I would like to know how to resolve this.

Why are my <appSettings> null when accessing them through my UserControl?

UPDATE 1

It seems my UserControl doesn't recognize the <appSettings> at all.

When I put this code in my UserControl Load event I get a nullreference as well.

private void SelectUser_Load(object sender, EventArgs e) { txtLocation.Text = ConfigurationManager.AppSettings["location"].ToString(); }

解决方案

I found the solution, in designmode the usercontrol already executes the code in the Load-event. Because the App.config isn't available in designmode it isn't found and therefore not loaded. So I made a little check around it to check if in designmode or not:

bool designMode = (LicenseManager.UsageMode == LicenseUsageMode.Designtime); if (designMode) { string location = ConfigurationManager.AppSettings["location"].ToString(); }