WinForms Designer Exception

Question

A WinForms form that includes a UserControl throws an exception when I attempt to display it in design mode, but runs properly when the program is ran or debugged.

The designer says:

The variable 'fpInfoA' is either undeclared or was never assigned.
ResearchTool fMain.Designer.cs Line:282 Column:1 Call Stack
at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.Error(IDesignerSerializationManager manager, String exceptionText, String helpLink) at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializeExpression(IDesignerSerializationManager manager, String name, CodeExpression expression) at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializeExpression(IDesignerSerializationManager manager, String name, CodeExpression expression) at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializeStatement(IDesignerSerializationManager manager, CodeStatement statement)

However, it looks like the variable is assigned as I would expect in InitializeComponent

private void InitializeComponent()
{
    // ... (Order of statements is same as in actual code) ...
    this.tpFpA = new System.Windows.Forms.TabPage();
    this.fpInfoA = new ResearchTool.FPInfo();
    // ...
    this.tpFpA.Controls.Add(this.fpInfoA); // THIS LINE BLOWS UP IN DESIGN MODE
}

Thoughts on how to track down this issue? For example, is there a way to debug initialization of the designer?

Answer 1

One workaround in case you can't fix the issue, would be to surround the offending bits of code with checks for DesignMode.

As in:

private void InitializeComponent()
{
    ...
    if(!DesignMode)
    {
        this.fpInfoA = new ResearchTool.FPInfo();
    }
    ...
}

This can also speed it up a little bit if it's doing things that aren't needed in design mode and that are quite slow, like connecting to databases or similar.