如何在QT中更新窗口？

Question

Im working on a simple project in QtCreator where you input text into a line_edit which then gets printed after clicking a button. It works but I need to resize the window in order to see the updated/changed display.

So starting off with the main.cpp, I have left it as default after some tests:

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

That has the issue I was talking about above. I decided to add w.update(); and see if that fixed the issue, it did not. I thought maybe it was because the program was not looping, so I entered the code in a while(true) loop which also was to no avail.

The mainwindow.cpp file is as follows:

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    connect(ui->textBtn, SIGNAL(clicked(bool)), this, SLOT(setText()));
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::setText()
{
    QString temp = ui->inputText->text();
    ui->displayLabel->setText(temp);

}

MainWindow.hpp:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

public slots:
    void setText();

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

Is there a QObject or predifined function in QT that allows me to update the window or automatically updates the window after a detected user change?

Edit: The UI file might be of importance as well:

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>554</width>
    <height>463</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralWidget">
   <widget class="QLabel" name="displayLabel">
    <property name="geometry">
     <rect>
      <x>140</x>
      <y>150</y>
      <width>251</width>
      <height>91</height>
     </rect>
    </property>
    <property name="text">
     <string/>
    </property>
    <property name="scaledContents">
     <bool>true</bool>
    </property>
    <property name="wordWrap">
     <bool>true</bool>
    </property>
   </widget>
   <widget class="QWidget" name="layoutWidget">
    <property name="geometry">
     <rect>
      <x>130</x>
      <y>30</y>
      <width>251</width>
      <height>81</height>
     </rect>
    </property>
    <layout class="QVBoxLayout" name="verticalLayout">
     <item>
      <widget class="QLineEdit" name="inputText"/>
     </item>
     <item>
      <widget class="QPushButton" name="textBtn">
       <property name="text">
        <string>Display Text</string>
       </property>
      </widget>
     </item>
    </layout>
   </widget>
  </widget>
  <widget class="QMenuBar" name="menuBar">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>554</width>
     <height>22</height>
    </rect>
   </property>
  </widget>
  <widget class="QToolBar" name="mainToolBar">
   <attribute name="toolBarArea">
    <enum>TopToolBarArea</enum>
   </attribute>
   <attribute name="toolBarBreak">
    <bool>false</bool>
   </attribute>
  </widget>
  <widget class="QStatusBar" name="statusBar"/>
 </widget>
 <layoutdefault spacing="6" margin="11"/>
 <resources/>
 <connections/>
</ui>

Answer 1

The problem is not the update of the GUI but the QLabel does not change size, the initial size depends on the initial text, and if you set a text with larger size only part of the text will be displayed. To adjust the size of the label to the size of the text you must use adjustSize() :

void MainWindow::setText()
{
    QString temp = ui->inputText->text();
    ui->displayLabel->setText(temp);
    ui->displayLabel->adjustSize();
}

On the other hand in Qt5 it is advisable to use the new connection syntax since they have several advantages as indicated by the docs , in your case you must change your code to:

connect(ui->textBtn, &QPushButton::clicked, this, &MainWindow::setText);