Value cannot be null. Parameter name: existingConnection

Lakshmanan B 81

Hi,

I am quite new to Visual Studio development and I am working on a hobby project using WPF application with C#. I currently exploring User Control in WPF application. So, I have a project named "wpfLearnMainWin" say parent project (that has app.xaml and mainWindow.xaml), and an other project named "wpfLearnUserCon" say child project. This child project has several user controls such as "newItem.xaml", "settings.xaml", "about.xaml", "info.xaml".

In the mainWIndow.xaml, I have used a "Tab Control" where each tabs takes us to "new item", "about", "settings" and "info". So, in the mainwindow, if I click "settings", it should load the "settings.xaml" user control in the settings section. I have dragged and dropped the "settings" user control into the mainwindow under the settings tab section.

But, here I am facing an issue and the issue is "Value cannot be null. Parameter name: existingConnection".

In the mainWindow.xaml code, this particular line has this blue curly lines and shows

User's image

The error is attached below.
User's image In fact, in the designer window it shows an "x" mark like the image below.

User's image

Can someone help me with this regard? TIA

Viorel 118.2K Reputation points

2024-04-19T13:46:33.8033333+00:00

Probably the RlcpDeviceManagerView has an issue. (For example: the constructor cannot be executed). Show some details about the Settings.
Hui Liu-MSFT 48,571 Reputation points Microsoft Vendor

2024-04-22T02:42:58.6233333+00:00

Hi,@Lakshman Balasubramanian. Welcome to Microsoft Q&A. Could you show a minimal, reproducible example without private information so I can reproduce the issue? If your question is more complete and clear, you may get a more accurate solution.
Lakshmanan B 81 Reputation points

2024-04-22T10:46:41.0966667+00:00

Hi, thanks for your response. As Viorel in the above reply mentioned, The constructor is failing to execute because of the following reason. When I debugged traced back to code, it lead me to one of the constructor in the Data.cs where in the base contructor I am called GetDBConnection() which must return true but unfortunately it returns null. Here in Data.cs, I am trying to establish an SQL data. For some reason the SQL data is not created and it throws an exception.

Exception thrown: 'System.Data.SqlServerCe.SqlCeException' in System.Data.SqlServerCe.dll
Exception thrown: 'System.ArgumentNullException' in EntityFramework.dll

I believe this might be the reason that is stopping me from executing the application.

The sample code to connect to the DB is here:

GetDBConnection() {
string dbfile = sampleData.sdf;
string dbpath = Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData);

dbpath = Path.Combine(dbpath, "SampleFolder");

if(Directory.Exists(dbpath) == false)

{

Directory.CreateDirectory(dbpath);

DirectoryInfo info = new DirectoryInfo(dbpath);

DirectorySecurity security = info.GetAccessControl();

security.AddAccessRule(

new FileSystemAccessRule(Environment.UserName,

FileSystemRights.FullControl,

InheritanceFlags.ContainerInherit | InheritanceFlags.ObjectInherit,

PropagationFlags.InheritOnly,

AccessControlType.Allow));

info.SetAccessControl(security);

}

dbpath = Path.Combine(dbpath, dbfile);

m_dbpath = dbpath;

m_ConnectionString = string.Format("Data Source='{0}';Password=password", dbpath);

Console.WriteLine(m_ConnectionString);

if(File.Exists(m_dbpath) == false)

{

SqlCeEngine eng = new SqlCeEngine(m_ConnectionString);

eng.CreateDatabase();

}

SqlCeConnection ceconn = new SqlCeConnection(m_ConnectionString);

ceconn.Open();

}
Hui Liu-MSFT 48,571 Reputation points Microsoft Vendor

2024-04-23T09:53:45.87+00:00

The exception indicates that there is a problem establishing a connection to the database, and it's likely happening within the GetDBConnection() method.

You could try to do following check.

Database File Existence: Ensure that the SQL database file (sampleData.sdf) exists at the specified path (dbpath). You can check this by verifying the existence of the file using File.Exists() method.

Database Engine Initialization: Make sure that the SQL database engine is properly initialized. The code snippet you provided attempts to create the database file if it doesn't exist, but ensure that this operation is successful.

Connection String: Double-check the connection string (m_ConnectionString) to ensure it's correctly formatted and pointing to the correct database file.

Database Permissions: Ensure that the application has sufficient permissions to access and modify the database file. The code snippet sets appropriate permissions using FileSystemAccessRule, but double-check to ensure it's correctly applied.

Exception Handling: Wrap the database connection code in a try-catch block to handle any exceptions gracefully. Log the exception details to identify the specific cause of the connection failure.

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Value cannot be null. Parameter name: existingConnection

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