How to set form control property from function

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How do I set the value of the Text property of my label1 on Form1, from within a function in the main project cpp file?

I can do it within the event handler inside the class, but that would mean writing all my code within the header file (Form1.h). Surely that's not correct practice????

Within fnTest() the intellisense prompts to the WindowsForms::Form1::label1, so that seems to be recognised.

I'm guessing the answer is simple (probably almost embarrasingly so - a head-slapping moment!), but I've searched the net (& this site) trying to get an answer without success. Maybe I'm using the wrong search terminology. The examples I can find all show the code residing in the event handlers in the header file, which I can already get to work, but I don't like the idea of that for code portability.

Posting the code but it is the stock standard IDE generated code. All I've added is fnTest() & the code inside the Form1_Load() handler.

Thanks in advance,
Dave.

Form1.h

#pragma once

void fnTest(int);

namespace WindowsForms {

    using namespace System;
    using namespace System::ComponentModel;
    using namespace System::Collections;
    using namespace System::Windows::Forms;
    using namespace System::Data;
    using namespace System::Drawing;

    /// <summary>
    /// Summary for Form1
    ///
    /// WARNING: If you change the name of this class, you will need to change the
    ///          'Resource File Name' property for the managed resource compiler tool
    ///          associated with all .resx files this class depends on.  Otherwise,
    ///          the designers will not be able to interact properly with localized
    ///          resources associated with this form.
    /// </summary>
    public ref class Form1 : public System::Windows::Forms::Form
    {
    public:
        Form1(void)
        {
            InitializeComponent();
            //
            //TODO: Add the constructor code here
            //
        }

    protected:
        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        ~Form1()
        {
            if (components)
            {
                delete components;
            }
        }
    public: System::Windows::Forms::Label^  label1;
    protected:

    private:
        /// <summary>
        /// Required designer variable.
        /// </summary>
        System::ComponentModel::Container ^components;

#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->label1 = (gcnew System::Windows::Forms::Label());
            this->SuspendLayout();
            //
            // label1
            //
            this->label1->BorderStyle = System::Windows::Forms::BorderStyle::Fixed3D;
            this->label1->Location = System::Drawing::Point(34, 38);
            this->label1->Name = L"label1";
            this->label1->Size = System::Drawing::Size(100, 20);
            this->label1->TabIndex = 0;
            this->label1->Text = L"label1";
            this->label1->TextAlign = System::Drawing::ContentAlignment::MiddleCenter;
            //
            // Form1
            //
            this->AutoScaleDimensions = System::Drawing::SizeF(6, 13);
            this->AutoScaleMode = System::Windows::Forms::AutoScaleMode::Font;
            this->ClientSize = System::Drawing::Size(284, 264);
            this->Controls->Add(this->label1);
            this->Name = L"Form1";
            this->Text = L"Form1";
            this->Load += gcnew System::EventHandler(this, &Form1::Form1_Load);
            this->ResumeLayout(false);

        }
#pragma endregion
    private: System::Void Form1_Load(System::Object^  sender, System::EventArgs^  e) {
                 label1->Text = "10";
                 fnTest();
             }
    };
}

C++ Test WinForms.cpp

// C++ Test WinForms.cpp : main project file.

#include "stdafx.h"
#include "Form1.h"

using namespace WindowsForms;

[STAThreadAttribute]
int main(array<System::String ^> ^args)
{
    // Enabling Windows XP visual effects before any controls are created
    Application::EnableVisualStyles();
    Application::SetCompatibleTextRenderingDefault(false);

    // Create the main window and run it
    Application::Run(gcnew Form1());
    return 0;
}

void fnTest() {
    WindowsForms::Form1::label1->Text = "11"; // <- this is the line that fails to build

}

Posted 12-Mar-11 0:16am

DaveLock

Updated 12-Mar-11 14:19pm

Sergey Alexandrovich Kryukov

v2

Add a Solution

2 solutions

Solution 1

It chops the code for Form1.h

...

#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->label1 = (gcnew System::Windows::Forms::Label());
this->SuspendLayout();
//
// label1
//
this->label1->BorderStyle = System::Windows::Forms::BorderStyle::Fixed3D;
this->label1->Location = System::Drawing::Point(34, 38);
this->label1->Name = L"label1";
this->label1->Size = System::Drawing::Size(100, 20);
this->label1->TabIndex = 0;
this->label1->Text = L"label1";
this->label1->TextAlign = System::Drawing::ContentAlignment::MiddleCenter;
//
// Form1
//
this->AutoScaleDimensions = System::Drawing::SizeF(6, 13);
this->AutoScaleMode = System::Windows::Forms::AutoScaleMode::Font;
this->ClientSize = System::Drawing::Size(284, 264);
this->Controls->Add(this->label1);
this->Name = L"Form1";
this->Text = L"Form1";
this->Load += gcnew System::EventHandler(this, &Form1::Form1_Load);
this->ResumeLayout(false);
}
#pragma endregion
private: System::Void Form1_Load(System::Object^ sender, System::EventArgs^ e) {
label1->Text = "10";
fnTest();
}
};
}

Posted 12-Mar-11 0:29am

DaveLock

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Espen Harlinn · Accepted Answer · 2011-03-12T00:33:00

You need to access an instance object of your Form1 class - you can do something like this:

1. Add the following to your Form1 class definition - leaving label1 as a public field is usually not considered a good idea.

public:
 void SetLabel1Text(String^ txt)
 {
   label1->Text = txt;
 }

2. Access your new method through an instance reference to an object of type Form1

Form1^ mainForm = gcnew Form1();
mainForm->SetLabel1Text( L"Some text" );
// This should also work as long as label1 is public:
//   mainForm->label1->Text = L"Some text";
Application::Run(mainForm);

C++

private: System::Void Form1_Load(System::Object^   sender, System::EventArgs^ e) 
{
 label1->Text = "10"; // <-- works because Form1_Load a non-static member function of the Form1 class
 fnTest(); // <-- this method is not part of your class and needs access to an instance of your Form1 class
}

Update
This works like a charm (You should only have one message loop - Application::Run - in your program):

// SampleWinforms.cpp : main project file.

#include "stdafx.h"
#include "Form1.h"

using namespace SampleWinforms;

[STAThreadAttribute]
int main(array<System::String ^> ^args)
{
    // Enabling Windows XP visual effects before any controls are created
    Application::EnableVisualStyles();
    Application::SetCompatibleTextRenderingDefault(false);

    // Create the main window and run it
    Form1^ mainForm = gcnew Form1();
    mainForm->label1->Text = L"Some Text";
    Application::Run(mainForm);
    return 0;
}

I've added a button "button1" and assigned the following event handler

private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) 
{
 Form1^ newForm = gcnew Form1();
 newForm->label1->Text = L"Some Text On New Form";
 newForm->Show();
}

This lets me create a new window and modify the label before showing it.

Update 2
To change the Text property of label1 on the current form:

private: System::Void button2_Click(System::Object^  sender, System::EventArgs^  e) 
{ 
 label1->Text = L"Some Text On the Current Form"; 
}

Assuming that there will only be a single instance of Form1, the following adds a static property Instance enabling you to write something like Form::Instance->label1->Text = L"Simple singleton";.
Since Form::Instance is static it will allow you to access the form, as long as it exists, from any code that includes the "form1.h"

C++

public ref class Form1 : public System::Windows::Forms::Form
 {
private:
  typedef System::Windows::Forms::Form base;

  static Form1^ instance;
public:
  Form1(void)
  {
   InitializeComponent();
   instance = this;
  }

  property static Form1^ Instance
  {
   Form1^ get()
   {
    return instance;
   }
  }

protected:
  virtual void OnFormClosed(FormClosedEventArgs^ e) override
  {
   base::OnFormClosed(e);
   instance = nullptr; 
  }
// Rest of definition
}

Regards
Espen Harlinn