How to shrink a QMainWindow when its central widget is shrinked

[franky]

Hi all,

Please take a look at these files:

List.h:

#ifndef LIST_H
#define LIST_H
 
#include <QMainWindow>
#include "task.h"
#include <QVector>
 
class QLabel;
class QPushButton;
class QHBoxLayout;
class QVBoxLayout;
 
class List : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit List(QWidget *parent = nullptr);
    void updateStatus();
    ~List();
 
public slots:
    void addTask();
    void removeTask(Task*);
    void taskStatusChanged();
 
private:
    QVector<Task*> mTasks;
    QLabel* statusLabel;
    QPushButton* addTaskButtun;
    QHBoxLayout* hBox;
    QVBoxLayout* vBox;
};
 
#endif // LIST_H

#ifndef LIST_H
#define LIST_H

#include <QMainWindow>
#include "task.h"
#include <QVector>

class QLabel;
class QPushButton;
class QHBoxLayout;
class QVBoxLayout;

class List : public QMainWindow
{
    Q_OBJECT

public:
    explicit List(QWidget *parent = nullptr);
    void updateStatus();
    ~List();

public slots:
    void addTask();
    void removeTask(Task*);
    void taskStatusChanged();

private:
    QVector<Task*> mTasks;
    QLabel* statusLabel;
    QPushButton* addTaskButtun;
    QHBoxLayout* hBox;
    QVBoxLayout* vBox;
};

#endif // LIST_H

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List.cpp:

#include "list.h"
#include <QPushButton>
#include <QLabel>
#include <QHBoxLayout>
#include <QVBoxLayout>
#include <QString>
#include <QInputDialog>
#include <QLineEdit>
 
List::List(QWidget *parent)
    : QMainWindow(parent), mTasks()
{
    statusLabel = new QLabel(tr("Status: 0 todo / 0 done"));
    addTaskButtun = new QPushButton(tr("Add task"));
 
    hBox = new QHBoxLayout;
    hBox->addWidget(statusLabel);
    hBox->addStretch();
    hBox->addWidget(addTaskButtun);
 
    vBox = new QVBoxLayout;
    vBox->addLayout(hBox);
    vBox->addStretch();
 
    QWidget *widget = new QWidget;
    widget->setLayout(vBox);
    setCentralWidget(widget);
 
    connect(addTaskButtun, &QPushButton::clicked, this, &List::addTask);
    updateStatus();
}
 
//************************************************
 
void List::addTask() {
   bool ok;
   QString name = QInputDialog::getText(this, tr("Add Task"), tr("Task name"),
                                       QLineEdit::Normal, tr("Untitled task"), &ok);
 
   if(ok && !name.isEmpty()) {
       Task* task = new Task(name);
       connect(task, &Task::removed, this, &List::removeTask);
       connect(task, &Task::statusChanged, this, &List::taskStatusChanged);
       mTasks.append(task);
       vBox->addWidget(task);
       updateStatus();
   }
}
 
//*********************************************
 
void List::removeTask(Task* task) {
   mTasks.removeOne(task);
   vBox->removeWidget(task);
   delete task;
   updateStatus();
}
 
//**************************************
 
void List::taskStatusChanged() {
    updateStatus();
}
 
//************************************
 
void List::updateStatus() {
    int completedCount = 0;
 
    for(auto t: mTasks)
        if(t->isCompleted())
            completedCount++;
 
    int todoCount = mTasks.size() - completedCount;
    statusLabel->setText(QString("Statuse: %1 todo / %2 completed")
                                .arg(todoCount) .arg(completedCount));
}
 
//*****************************
 
List::~List()
{
    delete vBox;
}

#include "list.h"
#include <QPushButton>
#include <QLabel>
#include <QHBoxLayout>
#include <QVBoxLayout>
#include <QString>
#include <QInputDialog>
#include <QLineEdit>

List::List(QWidget *parent)
    : QMainWindow(parent), mTasks()
{
    statusLabel = new QLabel(tr("Status: 0 todo / 0 done"));
    addTaskButtun = new QPushButton(tr("Add task"));

    hBox = new QHBoxLayout;
    hBox->addWidget(statusLabel);
    hBox->addStretch();
    hBox->addWidget(addTaskButtun);

    vBox = new QVBoxLayout;
    vBox->addLayout(hBox);
    vBox->addStretch();

    QWidget *widget = new QWidget;
    widget->setLayout(vBox);
    setCentralWidget(widget);

    connect(addTaskButtun, &QPushButton::clicked, this, &List::addTask);
    updateStatus();
}

//************************************************

void List::addTask() {
   bool ok;
   QString name = QInputDialog::getText(this, tr("Add Task"), tr("Task name"),
                                       QLineEdit::Normal, tr("Untitled task"), &ok);

   if(ok && !name.isEmpty()) {
       Task* task = new Task(name);
       connect(task, &Task::removed, this, &List::removeTask);
       connect(task, &Task::statusChanged, this, &List::taskStatusChanged);
       mTasks.append(task);
       vBox->addWidget(task);
       updateStatus();
   }
}

//*********************************************

void List::removeTask(Task* task) {
   mTasks.removeOne(task);
   vBox->removeWidget(task);
   delete task;
   updateStatus();
}

//**************************************

void List::taskStatusChanged() {
    updateStatus();
}

//************************************

void List::updateStatus() {
    int completedCount = 0;

    for(auto t: mTasks)
        if(t->isCompleted())
            completedCount++;

    int todoCount = mTasks.size() - completedCount;
    statusLabel->setText(QString("Statuse: %1 todo / %2 completed")
                                .arg(todoCount) .arg(completedCount));
}

//*****************************

List::~List()
{
    delete vBox;
}

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Task.h:

#ifndef TASK_H
#define TASK_H
 
#include <QWidget>
#include <QString>
 
class QCheckBox;
class QPushButton;
class QHBoxLayout;
 
class Task : public QWidget
{
    Q_OBJECT
 
public:
    explicit Task(const QString&, QWidget* parent = nullptr);
 
    void setName(const QString&);
    QString name() const;
    bool isCompleted() const;
 
    ~Task();
 
public slots:
    void rename();
 
signals:
   void removed(Task*);
   void statusChanged(Task*);
 
private slots:
   void checked(bool);
 
private:
   QCheckBox* checkbox;
   QPushButton* editButton;
   QPushButton* removeButton;
   QHBoxLayout* hBox;
};
 
#endif // TASK_H

#ifndef TASK_H
#define TASK_H

#include <QWidget>
#include <QString>

class QCheckBox;
class QPushButton;
class QHBoxLayout;

class Task : public QWidget
{
    Q_OBJECT

public:
    explicit Task(const QString&, QWidget* parent = nullptr);

    void setName(const QString&);
    QString name() const;
    bool isCompleted() const;

    ~Task();

public slots:
    void rename();

signals:
   void removed(Task*);
   void statusChanged(Task*);

private slots:
   void checked(bool);

private:
   QCheckBox* checkbox;
   QPushButton* editButton;
   QPushButton* removeButton;
   QHBoxLayout* hBox;
};

#endif // TASK_H

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Task.cpp:

#include "task.h"
#include "list.h"
#include <QInputDialog>
#include <QWidget>
#include <QHBoxLayout>
#include <QPushButton>
#include <QCheckBox>
 
Task::Task(const QString& name, QWidget* parent) : QWidget (parent)
{
    checkbox = new QCheckBox;
    editButton = new QPushButton(tr("Edit"));
    removeButton = new QPushButton(tr("Remove"));
 
    hBox = new QHBoxLayout;
    hBox->addWidget(checkbox);
    hBox->addStretch();
    hBox->addWidget(editButton);
    hBox->addWidget(removeButton);
 
    setLayout(hBox);
 
    setName(name);
 
    connect(editButton, &QPushButton::clicked, this, &Task::rename);
    connect(removeButton, &QPushButton::clicked, [this]()->void {
        emit removed(this);
            });
    connect(checkbox, &QCheckBox::toggled, this, &Task::checked);
};
 
//*************************************
 
void Task::setName(const QString& name) {
    checkbox->setText(name);
}
 
//********************************************
 
QString Task::name() const {
    return checkbox->text();
}
 
//*****************************
 
bool Task::isCompleted() const {
    return checkbox->isChecked();
}
 
//****************************************
 
void Task::rename() {
    bool ok;
    QString value = QInputDialog::getText(this, tr("Edit task"), tr("Task name"),
                                          QLineEdit::Normal, this->name(), &ok);
    if(ok && !value.isEmpty())
        setName(value);
}
 
//************************************
 
void Task::checked(bool checked) {
    QFont font(checkbox->font());
    font.setStrikeOut(checked);
    checkbox->setFont(font);
 
    emit statusChanged(this);
}
 
//**************************************************
 
Task::~Task() {
    delete hBox;
}

#include "task.h"
#include "list.h"
#include <QInputDialog>
#include <QWidget>
#include <QHBoxLayout>
#include <QPushButton>
#include <QCheckBox>

Task::Task(const QString& name, QWidget* parent) : QWidget (parent)
{
    checkbox = new QCheckBox;
    editButton = new QPushButton(tr("Edit"));
    removeButton = new QPushButton(tr("Remove"));

    hBox = new QHBoxLayout;
    hBox->addWidget(checkbox);
    hBox->addStretch();
    hBox->addWidget(editButton);
    hBox->addWidget(removeButton);

    setLayout(hBox);

    setName(name);

    connect(editButton, &QPushButton::clicked, this, &Task::rename);
    connect(removeButton, &QPushButton::clicked, [this]()->void {
        emit removed(this);
            });
    connect(checkbox, &QCheckBox::toggled, this, &Task::checked);
};

//*************************************

void Task::setName(const QString& name) {
    checkbox->setText(name);
}

//********************************************

QString Task::name() const {
    return checkbox->text();
}

//*****************************

bool Task::isCompleted() const {
    return checkbox->isChecked();
}

//****************************************

void Task::rename() {
    bool ok;
    QString value = QInputDialog::getText(this, tr("Edit task"), tr("Task name"),
                                          QLineEdit::Normal, this->name(), &ok);
    if(ok && !value.isEmpty())
        setName(value);
}

//************************************

void Task::checked(bool checked) {
    QFont font(checkbox->font());
    font.setStrikeOut(checked);
    checkbox->setFont(font);

    emit statusChanged(this);
}

//**************************************************

Task::~Task() {
    delete hBox;
}

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When I add tasks "untitled task 1" to "untitled task 3", image number 1 below:

3.jpg

then remove "untitled task 2", the frame/window doesn't shrink and the space for that task is just vacant, image number 2. I like it to decrease and fit the remained tasks, like image number 3. When a task is added, the window increases in size, so when one is removed, it should decrease in size too.

I tested the followings one by one in void List::updateStatus() {, but none worked as expected!

What should be used instead, please?

this->sizeHint();
this->update();
this->resize(sizeHint());
this->adjustSize();

this->sizeHint();
this->update();
this->resize(sizeHint());
this->adjustSize();

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[d_stranz]

I think it is because in the List constructor, you add stretch to the vbox layout. The Task widgets you add go below that, so when you remove one, the stretch just expands to fill the empty space in between the hbox and the first remaining task.

Try not using the stretch at all. If that doesn't work, try using QBoxLayout::insertWidget() instead of addWidget() (which appends the new widget to the end of the layout, thus "trapping" the stretch between it and the start of the layout). In this case, your code would look something like this (assuming you still add the stretch during construction):

vbox->insertWidget( vbox->count() - 1, task );

vbox->insertWidget( vbox->count() - 1, task );

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I don't know if this will solve the non-shrink problem, but at least you won't have a gap when you remove a task because the stretch will always be at the end of the layout.

[franky]

Neither worked unfortunately!

Without vBox->addStretch();, shrink won't be applied but merely we have a sparsely populated area, after removing some tasks:

3.png

And when I keep vBox->addStretch();, and use vBox->insertWidget(vBox->count() - 1, task); instead of vBox->addWidget(task);, we will have this, once again:

3.png

[d_stranz]

Yes, your second screen shot is what I expected to see.

What you will probably have to do is implement a resize() on your List window when you remove a Task. In that slot, get the size of the List window -before- removing the Task, get the size of the Task itself, remove it, then resize the List height to be the original height minus the Task height.

[franky]

Good, thanks. There's always a way in programming!

I added the slot in List, but I think inside it, vBox should be resized, not? (And not the central widget of QMainWindow)

[d_stranz]

The QMainWindow is in charge of resizing its contents. I am pretty sure it asks the layout for the central widget for its size hint and adds the frame, menu bars, toolbars, status bars sizes as appropriate. So if the vbox layout never shrinks, it will return a size hint that includes the empty space.

But try it out to resize the vbox. If it works, it works. Riht now, I don't see any method in the QVBoxLayout class (or its base classes) that allows you to directly set the size.

[franky]

Thanks.

I was actually much dealt with height() and width() in the List.cpp file, but these two both belong to the central widget and hence, I couldn't make the job done using them.
How to access the height/width of the base class (QMainWindow) which is indeed in charge of the overall size, please, so that we can modify it when a remove is accomplished?

[d_stranz]

Your List class is derived from QMainWindow, isn't it? If your slots to add / remove new Task widgets are in the List class, then you can just call "height()" in those slots and you will get the height of the List widget. You then just call resize() after you compute the new height.

You don't want to change the height using the pointer to the central widget because QMainWindow (List) and the layout won't let it happen.

[franky]

Your List class is derived from QMainWindow, isn't it? If your slots to add / remove new Task widgets are in the List class, then you can just call "height()" in those slots and you will get the height of the List widget. You then just call resize() after you compute the new height.

I added resize(height() - 100, width()) to removeTask, (-100, just to test):

void List::removeTask(Task* task) {
   mTasks.removeOne(task);
   vBox->removeWidget(task);
   delete task;
   updateStatus();
 
   resize(height() - 100, width());
}

void List::removeTask(Task* task) {
   mTasks.removeOne(task);
   vBox->removeWidget(task);
   delete task;
   updateStatus();

   resize(height() - 100, width());
}

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When I hover the mouse on height(), this message is shown:
inline int QWidget::height() const , so that QWidget in our example is List, right?

So in that slot, when we use resize via a smaller height, the widget List must resize normally, and since this slot is called each time we remove a Task, therefore List is expected to shrink that way.

But it doesn't work as expected!

[d_stranz]

But it doesn't work as expected!

Well, what does happen? Anything? Nothing?

You should probably call "task->deleteLater()" instead of "delete task". You are in the middle of a slot, and control needs to return to the event loop so that Qt can clean up properly and take whatever other action is needed to redraw the UI. deleteLater() will delete the widget when the event loop runs.

[franky]

Very good, thanks for the precious info. I use the function this way:

void List::removeTask(Task* task) {
   mTasks.removeOne(task);
   vBox->removeWidget(task);
   task->deleteLater();
   updateStatus();
 
   resize(height() - 100, width());
}

void List::removeTask(Task* task) {
   mTasks.removeOne(task);
   vBox->removeWidget(task);
   task->deleteLater();
   updateStatus();

   resize(height() - 100, width());
}

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After entering 5 tasks:

3.PNG

And then deleting the first four ones, I got this! It's actually the way I meant I doesn't work.

4.PNG