CODEWITHSUNDEEP
.netwinformsvisual-studio-2008visual-c++
Vishal Kotcherlakota
Vishal Kotcherlakota

Reputation: 1154

Why does Visual C++ Designer not work after I added a control to my form?

My wanted to turn on double buffering in a panel, but the only way we could get the DoubleBuffered property to turn on was to create a new class that inherited from System::Windows::Form::Panel, like so:

#include "stdafx.h"

public ref class CPPIConfig: public System::Windows::Forms::Panel
{
public: CPPIConfig()
        {
            this->DoubleBuffered = true;
        }
};

And our form looks like this, now:

#pragma once
#using <system.drawing.dll>
#include "CPPIConfig.h"

[...]

public ref class C3_User_Interface : public System::Windows::Forms::Form
    {
      [...]
      public: CPPIConfig^ pPPI;
      [...]
    }

void InitializeComponent(void)
    {
        [...]
        this->pPPI = (gcnew CPPIConfig());
        [...]
    }
[...]

It builds and runs, no problem. However, when I try to view the form in design mode now, I'm getting the following error:

C++ CodeDOM parser error: Line: 144, Column: 15 --- Unknown type 'CPPIConfig'. Please make sure that the assembly that contains this type is referenced. If this type is a part of your development project, make sure that the project has been successfully built.

My questions:

  1. Why does design mode not work, even if the code builds and runs? I've tried several clean builds, but that doesn't look to be the issue.
  2. Is there a way I can set DoubleBuffered to true without using this method?

Upvotes: 2

Views: 7839

Answers (5)

Steffen Buehler
Steffen Buehler

Reputation: 1

Here's what I experienced with this "C++ CodeDOM parser error:..." issue.

Suddenly, my VS2019 refused to load the designer for my Form1.h. I got exactly the same message as above. One year ago, there were no problems, but now I wanted to work on.

The surprising reason was that in the past I moved too many functions into another source file! Since I didn't want to have Form1.h too big, I replaced for instance

void Form1::foo()
{
}

by

void foo();

and created a foo.cpp with

#include "Form1.h"
void Form1::foo()
{
}

This now no longer works! One or two external functions are ok, but more than three cause the described effect.

So I put everything back into Form1.h and the issue was gone.

Upvotes: 0

Nabeel
Nabeel

Reputation: 67

I had an inherited class from Panel as well. In my case, I had placed this toolbox item in its own C# project with its own namespace. For reasons unknown, the designer worked at first implementation then broke after I attempted to use the inherited class in a second file.

To fix it, I changed the namespace of the C# project to match the consuming projects namespace, as well as explicitly specified it in the designer code:

Project1::InheritedPanel^

instead of simply

InheritedPanel^

Upvotes: 0

SavageFly
SavageFly

Reputation: 11

Try moving the control initializing below the suspendlayout. This allows the designer to render correctly without the CodeDOM parse error.

Original was something like 

#pragma region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
void InitializeComponent(void)
{
    this->lblMessage = (gcnew System::Windows::Forms::Label());
    this->SuspendLayout();
    // lblMessage
    this->lblMessage->Location = System::Drawing::Point(12, 230);
    //.....
}

New format

#pragma region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
void InitializeComponent(void)
{
    this->SuspendLayout();
    // lblMessage
    this->lblMessage = (gcnew System::Windows::Forms::Label());
    this->lblMessage->Location = System::Drawing::Point(12, 230);
    //.....
}

Upvotes: 1

Vishal Kotcherlakota
Vishal Kotcherlakota

Reputation: 1154

The big hangup here really stems from my mixture of managed vs. unmanaged code. I went to MSDN to read more about it, but the upshot is this: Visual Studio can't handle my CPPIConfig class within this context because it's unmanaged/native code.

From the answer provided for a similar question:

The Windows Forms Designer cannot reflect on mixed-mode EXEs. Make sure you compile with /clr:pure or move any class that require design time support (e.g. the components and controls on the form) to a class library project.

Reflection, as this MSDN page points out, is what the Design view is using to render the Form within the IDE. In a few words, this is what reflection is:

Reflection allows known data types to be inspected at runtime. Reflection allows the enumeration of data types in a given assembly, and the members of a given class or value type can be discovered. This is true regardless of whether the type was known or referenced at compile time. This makes reflection a useful feature for development and code management tools.

Ahh. This is starting to make sense.

There's two ways to fix this problem, as far as I can tell.

Use /clr:pure in your project properties. This changes the Common Language Runtime support for the project. From this MSDN page:

Pure assemblies (compiled with /clr:pure) can contain both native and managed data types, but only managed functions. Like mixed assemblies, pure assemblies allow interop with native DLLs through P/Invoke (see Using Explicit PInvoke in C++ (DllImport Attribute)), but C++ Interop features are not available. Moreover, pure assemblies cannot export functions that are callable from native functions because entry points in a pure assembly use the __clrcall calling convention.

Create a class library project. As the other answer suggested, if I move the files to a class library project and reference it that way, I wouldn't see this problem. As I understand it, it would make CPPIConfig managed code.

Ultimately, structural limitations make neither of those options viable, and in the interest of time, we've decided to forego double buffering on the panel for now. Oh well, at least I learned more about this environment!

Upvotes: 5

paulsm4
paulsm4

Reputation: 121881

If you Google for your error message, you'll find lots of hits:

C++ CodeDOM parser error:  Unknown type 'CPPIConfig'

Please post back if any of these help!

Upvotes: 0

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