C++/CLI - how to open a new form and back

问题:

I am creating an application where the front end has to be a Windows Form using C++/CLI. The form is used for login purpose.

In my form, I have a register button. On click of this button, a new form should open ( closing the login form ). I was able to achieve this by the following code:

Form^ rgForm = gcnew RegisterForm;
rgForm->Show();
this->Hide(); // using this->Close() was closing the application

Now I want to have a cancel button on the register form, whose click should open the login form again and close the register form. How do I achieve that?

( I am confused with the use of this->Hide(), does it mean that the form exists, we just did not show it, and so even after the register form visibility, the login form still exists? )

Update : Now current form handle is passed into register form constructor ( storing it as a private variable with the name loginForm in RegisterForm class ).

Following is the code for cancel button click:

// RegisterForm class constructor

RegisterForm(System::Windows::Forms::Form^ f)
{
    loginForm = f;
}

// Cancel button click

private: System::Void BtnCancel_Click(System::Object^  sender, System::EventArgs^  e) 
{
     loginForm->Show();
     this->Hide();
}

On cancel button click I am getting the exception : "object not set to instance".

Can someone please help me.

Thanks.

回答1:

Create a constructor for RegisterForm which accepts a System::Windows::Form ^ object, and pass this to it when you are instantiating it from within the login form class

Form^ rgForm = gcnew RegisterForm(this);
rgForm->Show();
this->Hide();

Assume the login form object is called otherform within the RegisterForm class. Once you're ready to bring it back, just call otherform->Show()

When you hide the form, it still exists, it is just not visible to the user.

EDIT: I got this to work just fine. Here are the modifications (not the full code) that I made to the form

Form2(Registration form)

Form2(System::Windows::Forms::Form ^ frm1)
    {
        otherform = frm1;
        InitializeComponent();

    }

private: System::Windows::Forms::Form ^ otherform;

private: System::Void Cancel_Click(System::Object^  sender, System::EventArgs^  e) {
             this->Hide();
             otherform->Show();

}

Form1(Login form)

#include "Form2.h"

private: System::Void Register_Click(System::Object^  sender, System::EventArgs^  e) {

             Form2 ^ frm2 = gcnew Form2(this);
             frm2->Show();
             this->Hide();
}

回答2:

Thereby , I would like to show my full code to help the others:-

Form2.h

#pragma once

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

namespace Form1 {



    /// <summary>
    /// Summary for Form2
    /// </summary>
    public ref class Form2 : public System::Windows::Forms::Form
    {



    private: System::Windows::Forms::Form ^ otherform;
    public:
        Form2(System::Windows::Forms::Form ^ o )
        {
            otherform = o;
            InitializeComponent();

            //
            //TODO: Add the constructor code here
            //
        }

    protected:
        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        ~Form2()
        {
            if (components)
            {
                delete components;
            }
        }
    private: System::Windows::Forms::Button^  button1;
    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->button1 = (gcnew System::Windows::Forms::Button());
            this->SuspendLayout();
            // 
            // button1
            // 
            this->button1->Location = System::Drawing::Point(147, 132);
            this->button1->Name = L"button1";
            this->button1->Size = System::Drawing::Size(102, 38);
            this->button1->TabIndex = 0;
            this->button1->Text = L"Menu";
            this->button1->UseVisualStyleBackColor = true;
            this->button1->Click += gcnew System::EventHandler(this, &Form2::button1_Click);
            // 
            // Form2
            // 
            this->AutoScaleDimensions = System::Drawing::SizeF(6, 13);
            this->AutoScaleMode = System::Windows::Forms::AutoScaleMode::Font;
            this->ClientSize = System::Drawing::Size(412, 295);
            this->Controls->Add(this->button1);
            this->Name = L"Form2";
            this->Text = L"Form2";
            this->Load += gcnew System::EventHandler(this, &Form2::Form2_Load);
            this->ResumeLayout(false);

        }
    #pragma endregion
    private: System::Void Form2_Load(System::Object^  sender, System::EventArgs^  e) {
             }
    private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) {
                 this->Hide();
             otherform->Show();

             }
    };






    ////////////////////////

}

回答3:

///////////////////////Form1.h
#pragma once
#include "stdafx.h"
#include "Form2.h"
namespace Form1 {

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
/// </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;
        }
    }
private: System::Windows::Forms::Button^  button1;
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->button1 = (gcnew System::Windows::Forms::Button());
        this->SuspendLayout();
        // 
        // button1
        // 
        this->button1->Location = System::Drawing::Point(140, 206);
        this->button1->Name = L"button1";
        this->button1->Size = System::Drawing::Size(75, 23);
        this->button1->TabIndex = 0;
        this->button1->Text = L"Login";
        this->button1->UseVisualStyleBackColor = true;
        this->button1->Click += gcnew System::EventHandler(this, &Form1::button1_Click);
        // 
        // Form1
        // 
        this->AutoScaleDimensions = System::Drawing::SizeF(6, 13);
        this->AutoScaleMode = System::Windows::Forms::AutoScaleMode::Font;
        this->ClientSize = System::Drawing::Size(377, 291);
        this->Controls->Add(this->button1);
        this->Name = L"Form1";
        this->Text = L"Form1";
        this->ResumeLayout(false);

    }
#pragma endregion
private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) {

         Form2 ^ frm2 = gcnew Form2(this);
         frm2->Show();
         this->Hide();


         }
};

}