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Since updating to 17.5.0 (as well as 17.5.1) I am unable to open winforms design files due to the following error:
Unable to cast object of type 'System.Data.SqlClient.SqlCommand' to type
'Microsoft.Data.SqlClient.SqlCommand'.
This only happens for forms using components from the System.Data.SqlClient namespace, such as SqlDataAdapter, SqlCommand, SqlConnection, etc. There really isn't any additional info provided in Visual Studio aside from that error message. The projects all target .NET Framework 4.8.
Nothing has changed with the code, and applications still compile and run as they did prior to the update. I'm not sure where to look to see what is causing this issue. The projects do not have a reference to Microsoft.Data.SqlClient in them so I'm not sure why it's trying to cast stuff to types in that assembly.
@cstauffer, Welcome to Microsoft Q&A, the error often means that there two different namespaces have the same class name. I recommend that you could use the class with the namespace like the following code:
System.Data.SqlClient.SqlConnection connection = new System.Data.SqlClient.SqlConnection();
System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand();
etc.
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(188.79999999999998, 54%, 28%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EJT%3C/text%3E%3C/svg%3E)
I have the same issue, have submitted a bug report:
https://developercommunity.visualstudio.com/t/Windows-Forms-designer-since-VS-175:-U/10303272
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Me too
@cstauffer, I also reproduced the problem. I also recommend that you could ask the Question in DC or follow other's submitted question.
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In my case, it appears that the old VS toolbox items for SqlCommand, SqlDataAdapter, etc. no longer appear to compile properly as part of the VS designer rendering code. I had to take them out of the .designer files and move the initialization code into the _Load event for the form. Once I did that, the designer would render the form again without errors.
Initially, the issue showed up as an error that it wouldn't render because it couldn't load Microsoft.Data.SqlClient version 3.0.0.0 (a DLL that I didn't use in my .NET 4.8 code, since that's something for .NET Core 3.0 or later), in case anyone is having that problem too.
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(51.2, 12%, 14%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3ETL%3C/text%3E%3C/svg%3E)
It is a strange issue with the designer. Everything still compiles and runs but you can no longer use the designer to edit the form. Here is a stack trace form the designer window:
at Microsoft.VSDesigner.Data.VS.SqlCommandDesigner.Initialize(IComponent component)
at System.ComponentModel.Design.DesignerHost.AddToContainerPostProcess(IComponent component, String name, IContainer containerToAddTo)
at System.ComponentModel.Design.DesignerHost.PerformAdd(IComponent component, String name)
at System.ComponentModel.Design.DesignerHost.System.ComponentModel.Design.IDesignerHost.CreateComponent(Type componentType, String name)
at System.ComponentModel.Design.Serialization.DesignerSerializationManager.CreateInstance(Type type, ICollection arguments, String name, Boolean addToContainer)
at System.ComponentModel.Design.Serialization.DesignerSerializationManager.System.ComponentModel.Design.Serialization.IDesignerSerializationManager.CreateInstance(Type type, ICollection arguments, String name, Boolean addToContainer)
at System.ComponentModel.Design.Serialization.ComponentCodeDomSerializer.DeserializeInstance(IDesignerSerializationManager manager, Type type, Object[] parameters, String name, Boolean addToContainer)
at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializeExpression(IDesignerSerializationManager manager, String name, CodeExpression expression)
at System.ComponentModel.Design.Serialization.CodeDomSerializer.DeserializeStatementToInstance(IDesignerSerializationManager manager, CodeStatement statement)
at System.ComponentModel.Design.Serialization.CodeDomSerializer.Deserialize(IDesignerSerializationManager manager, Object codeObject)
at System.ComponentModel.Design.Serialization.TypeCodeDomSerializer.DeserializeName(IDesignerSerializationManager manager, String name, CodeStatementCollection statements)
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(86.4, 84%, 18%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EKL%3C/text%3E%3C/svg%3E)
Even a fresh new project "Windows Forms" has the same problem.
When drag/drop a data component form the Toolbox like SqlCommand, SqlDataAdapter the message appears:
Failed to create component "SqlCommand"... System.InvalidCastException: Unable to cast object of type 'System.Data.SqlClient.SqlCommand' to type 'Microsoft.Data.SqlClient.Sqlcommand'