QWidget Problem !!

[Fatla]

Now , I'm @ QT Design then I create a normal widget ,add ctrls into it.
I make the previous step 4 times . So now I've 4 .UIs that have there own ctrls into it .
To Each UI, I create its (.h + .cpp ) to implement my own slots .
Well now I open ,using QT Design ,the 1st .ui I 've made & Drag & Drop Widget into it , which is located into Container Section .
The Problem : is how to make other .UIs open into the widget I created @ the 1st .ui I 've made .


The standard way that shows each .UI separately, wrks fine by :

// CustomSlot2 implements the slots inside the 2nd .UI
CustomSlot2* widget = new CustomSlot2();   
 widget->setAttribute(Qt::WA_DeleteOnClose);
  widget->show();

// CustomSlot2 implements the slots inside the 2nd .UI
CustomSlot2* widget = new CustomSlot2();   
 widget->setAttribute(Qt::WA_DeleteOnClose);
  widget->show();

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CustomSlot2 Constructor's Code is :

CustomSlot2::CustomSlot2(QWidget *parent): QWidget(parent)
 {
    formTwo.setupUi(this);
 
 }

CustomSlot2::CustomSlot2(QWidget *parent): QWidget(parent)
 {
    formTwo.setupUi(this);

 }

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So far so Good . However , by making this approach there's a flicker when you Open & Hide/Close Windows .

The MainWindow's header file generated by "make" :

class Ui_MainForm
{
public:
    QPushButton *btnProcess;
    QLineEdit *txtInput;
    QLineEdit *txtResult;
    QPushButton *btnNext;
    QWidget *widget;
//........................ etc

class Ui_MainForm
{
public:
    QPushButton *btnProcess;
    QLineEdit *txtInput;
    QLineEdit *txtResult;
    QPushButton *btnNext;
    QWidget *widget;
//........................ etc

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Thanks .