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Range-based for loop for a QList

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  • T Offline
    T Offline
    tomy
    wrote on 13 May 2020, 10:21 last edited by
    #1

    Hello all,

    Please take a look at my project.

    ListAdd.h:

    #ifndef LISTADD_H
    #define LISTADD_H
    
    #include <QDialog>
    #include <QAbstractButton>
    
    class QPushButton;
    class QListWidget;
    class QComboBox;
    class QDialogButtonBox;
    
    class ListAdd : public QDialog
    {
        Q_OBJECT
    
    public:
        ListAdd(QWidget *parent = nullptr);
    
    private slots:
        void addData();
        void save();
    
    private:
        void load();
        void btnClicked(QAbstractButton*);
    
        QComboBox* combo = nullptr;
        QPushButton* add = nullptr;
        QListWidget* list = nullptr;
        QDialogButtonBox* dBtBox = nullptr;
    };
    #endif // LISTADD_H
    

    ListAdd.cpp:

    #include "listadd.h"
    #include <QListWidget>
    #include <QComboBox>
    #include <QPushButton>
    #include <QDialogButtonBox>
    #include <QHBoxLayout>
    #include <QVBoxLayout>
    #include <QSettings>
    #include <QMessageBox>
    #include <QVariant>
    
    ListAdd::ListAdd(QWidget *parent)
        : QDialog(parent)
    {
        combo = new QComboBox;
        combo->setEditable(true);
        add = new QPushButton(tr("&Add"));
        list = new QListWidget;
        list->setSelectionMode(QAbstractItemView::ExtendedSelection);
    
        dBtBox = new QDialogButtonBox(QDialogButtonBox::Ok |
                                      QDialogButtonBox::Cancel);
        dBtBox->setEnabled(true);
        dBtBox->addButton("Clear", QDialogButtonBox::ButtonRole::ActionRole);
        dBtBox->addButton("Remove", QDialogButtonBox::ButtonRole::ActionRole);
    
        QHBoxLayout* topLayout = new QHBoxLayout;
        topLayout->addWidget(combo);
        topLayout->addWidget(add);
    
        QVBoxLayout* mainLayout = new QVBoxLayout;
        mainLayout->addLayout(topLayout);
        mainLayout->addWidget(list);
        mainLayout->addWidget(dBtBox);
    
        setLayout(mainLayout);
    
        connect(add, &QPushButton::clicked, this, &ListAdd::addData);
        connect(dBtBox, &QDialogButtonBox::clicked, this, &ListAdd::btnClicked);
        load();
    }
    
    //*******************************************
    
    void ListAdd::addData()
    {
        if(combo->findText(combo->currentText()) < 0)
            combo->addItem(combo->currentText());
    
        list->addItem(combo->currentText());
    }
    
    //*************************************************************
    
    void ListAdd::save()
    {
        QSettings settings("Me", "CS Company");
        settings.clear();
    
        settings.setValue("text",combo->currentText());
    
        settings.beginWriteArray("combo");
        for (int i=0; i<combo->count();i++)
        {
           settings.setArrayIndex(i);
           settings.setValue("item", combo->itemText(i));
        }
        settings.endArray();
    
        settings.beginWriteArray("list");
        for (int i=0; i<list->count();i++)
        {
           settings.setArrayIndex(i);
           settings.setValue("item", list->item(i)->text());
        }
        settings.endArray();
    }
    
    //********************************************************
    
    void ListAdd::load()
    {
     QSettings settings("Me", "CS Company");
    
     combo->setCurrentText(settings.value("text", "").toString());
    
     int comboSize = settings.beginReadArray("combo");
     for (int i=0; i<comboSize;i++)
     {
        settings.setArrayIndex(i);
        combo->addItem(settings.value("item", "").toString());
     }
     settings.endArray();
    
     int listSize = settings.beginReadArray("list");
     for (int i=0; i<listSize;i++)
     {
        settings.setArrayIndex(i);
        list->addItem(settings.value("item", "").toString());
     }
     settings.endArray();
    }
    
    //********************************************************************
    
    void ListAdd::btnClicked(QAbstractButton* button)
    {
        if(button->text().contains("OK"))
        {
            save();
            QMessageBox::information(this, "Saved", "Your data is saved! Please re-open the application");
        }
    
        else if(button->text().contains("Cancel"))
        {
            QMessageBox::information(this, "Quit", "Your data is being lost");
            accept();
        }
    
        else if(button->text().contains("Clear"))
        {
            list->clear();
            combo->clear();
        }
    
        else if(button->text().contains("Remove")) {
            QList<QListWidgetItem*> items = list->selectedItems();
    
            for(auto& item : items)
            {
                list->removeItemWidget(item);
                delete item;
            }
        }
    }
    

    The question is about the else-if condition above, which is, why without delete item;, won't the item be removed from the list, please?

    A 1 Reply Last reply 13 May 2020, 13:28
    0
    • C Offline
      C Offline
      Christian Ehrlicher
      Lifetime Qt Champion
      wrote on 13 May 2020, 10:27 last edited by
      #2

      @tomy said in Range-based for loop for a QList:

      The question is about the else-if condition above, which is, why without delete item;, won't the item be removed from the list, please?

      It's perfectly written in the documentation.

      Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
      Visit the Qt Academy at https://academy.qt.io/catalog

      T 1 Reply Last reply 13 May 2020, 10:56
      3
      • C Christian Ehrlicher
        13 May 2020, 10:27

        @tomy said in Range-based for loop for a QList:

        The question is about the else-if condition above, which is, why without delete item;, won't the item be removed from the list, please?

        It's perfectly written in the documentation.

        T Offline
        T Offline
        tomy
        wrote on 13 May 2020, 10:56 last edited by tomy
        #3

        @Christian-Ehrlicher

        What does "entirely" there mean?

        And the mysterious thing is that the first time I used:

        for(QListWidgetItem* item: items)
        

        And it used to work (remove the row from the list) without "delete", but not now.

        And one rather side-question, please. I think except for some rare situations like above that we manually need to delete a pointer, with the parent-child relationship, we needn't have to use a destructor in the projects. Right?

        jsulmJ B 2 Replies Last reply 13 May 2020, 11:01
        0
        • T tomy
          13 May 2020, 10:56

          @Christian-Ehrlicher

          What does "entirely" there mean?

          And the mysterious thing is that the first time I used:

          for(QListWidgetItem* item: items)
          

          And it used to work (remove the row from the list) without "delete", but not now.

          And one rather side-question, please. I think except for some rare situations like above that we manually need to delete a pointer, with the parent-child relationship, we needn't have to use a destructor in the projects. Right?

          jsulmJ Offline
          jsulmJ Offline
          jsulm
          Lifetime Qt Champion
          wrote on 13 May 2020, 11:01 last edited by
          #4

          @tomy Did you read this from the link:

          To remove an item (row) from the list entirely, either delete the item or use takeItem().
          

          ?

          https://forum.qt.io/topic/113070/qt-code-of-conduct

          1 Reply Last reply
          1
          • T tomy
            13 May 2020, 10:56

            @Christian-Ehrlicher

            What does "entirely" there mean?

            And the mysterious thing is that the first time I used:

            for(QListWidgetItem* item: items)
            

            And it used to work (remove the row from the list) without "delete", but not now.

            And one rather side-question, please. I think except for some rare situations like above that we manually need to delete a pointer, with the parent-child relationship, we needn't have to use a destructor in the projects. Right?

            B Offline
            B Offline
            Bonnie
            wrote on 13 May 2020, 11:04 last edited by Bonnie
            #5

            @tomy I think you must have used a different function.
            removeItemWidget does not remove a item.
            It removes the widget set by setItemWidget.
            If there's no widget set, it does nothing.
            But even you remove a item with takeItem, you still need to delete it manually.

            1 Reply Last reply
            1
            • T tomy
              13 May 2020, 10:21

              Hello all,

              Please take a look at my project.

              ListAdd.h:

              #ifndef LISTADD_H
              #define LISTADD_H
              
              #include <QDialog>
              #include <QAbstractButton>
              
              class QPushButton;
              class QListWidget;
              class QComboBox;
              class QDialogButtonBox;
              
              class ListAdd : public QDialog
              {
                  Q_OBJECT
              
              public:
                  ListAdd(QWidget *parent = nullptr);
              
              private slots:
                  void addData();
                  void save();
              
              private:
                  void load();
                  void btnClicked(QAbstractButton*);
              
                  QComboBox* combo = nullptr;
                  QPushButton* add = nullptr;
                  QListWidget* list = nullptr;
                  QDialogButtonBox* dBtBox = nullptr;
              };
              #endif // LISTADD_H
              

              ListAdd.cpp:

              #include "listadd.h"
              #include <QListWidget>
              #include <QComboBox>
              #include <QPushButton>
              #include <QDialogButtonBox>
              #include <QHBoxLayout>
              #include <QVBoxLayout>
              #include <QSettings>
              #include <QMessageBox>
              #include <QVariant>
              
              ListAdd::ListAdd(QWidget *parent)
                  : QDialog(parent)
              {
                  combo = new QComboBox;
                  combo->setEditable(true);
                  add = new QPushButton(tr("&Add"));
                  list = new QListWidget;
                  list->setSelectionMode(QAbstractItemView::ExtendedSelection);
              
                  dBtBox = new QDialogButtonBox(QDialogButtonBox::Ok |
                                                QDialogButtonBox::Cancel);
                  dBtBox->setEnabled(true);
                  dBtBox->addButton("Clear", QDialogButtonBox::ButtonRole::ActionRole);
                  dBtBox->addButton("Remove", QDialogButtonBox::ButtonRole::ActionRole);
              
                  QHBoxLayout* topLayout = new QHBoxLayout;
                  topLayout->addWidget(combo);
                  topLayout->addWidget(add);
              
                  QVBoxLayout* mainLayout = new QVBoxLayout;
                  mainLayout->addLayout(topLayout);
                  mainLayout->addWidget(list);
                  mainLayout->addWidget(dBtBox);
              
                  setLayout(mainLayout);
              
                  connect(add, &QPushButton::clicked, this, &ListAdd::addData);
                  connect(dBtBox, &QDialogButtonBox::clicked, this, &ListAdd::btnClicked);
                  load();
              }
              
              //*******************************************
              
              void ListAdd::addData()
              {
                  if(combo->findText(combo->currentText()) < 0)
                      combo->addItem(combo->currentText());
              
                  list->addItem(combo->currentText());
              }
              
              //*************************************************************
              
              void ListAdd::save()
              {
                  QSettings settings("Me", "CS Company");
                  settings.clear();
              
                  settings.setValue("text",combo->currentText());
              
                  settings.beginWriteArray("combo");
                  for (int i=0; i<combo->count();i++)
                  {
                     settings.setArrayIndex(i);
                     settings.setValue("item", combo->itemText(i));
                  }
                  settings.endArray();
              
                  settings.beginWriteArray("list");
                  for (int i=0; i<list->count();i++)
                  {
                     settings.setArrayIndex(i);
                     settings.setValue("item", list->item(i)->text());
                  }
                  settings.endArray();
              }
              
              //********************************************************
              
              void ListAdd::load()
              {
               QSettings settings("Me", "CS Company");
              
               combo->setCurrentText(settings.value("text", "").toString());
              
               int comboSize = settings.beginReadArray("combo");
               for (int i=0; i<comboSize;i++)
               {
                  settings.setArrayIndex(i);
                  combo->addItem(settings.value("item", "").toString());
               }
               settings.endArray();
              
               int listSize = settings.beginReadArray("list");
               for (int i=0; i<listSize;i++)
               {
                  settings.setArrayIndex(i);
                  list->addItem(settings.value("item", "").toString());
               }
               settings.endArray();
              }
              
              //********************************************************************
              
              void ListAdd::btnClicked(QAbstractButton* button)
              {
                  if(button->text().contains("OK"))
                  {
                      save();
                      QMessageBox::information(this, "Saved", "Your data is saved! Please re-open the application");
                  }
              
                  else if(button->text().contains("Cancel"))
                  {
                      QMessageBox::information(this, "Quit", "Your data is being lost");
                      accept();
                  }
              
                  else if(button->text().contains("Clear"))
                  {
                      list->clear();
                      combo->clear();
                  }
              
                  else if(button->text().contains("Remove")) {
                      QList<QListWidgetItem*> items = list->selectedItems();
              
                      for(auto& item : items)
                      {
                          list->removeItemWidget(item);
                          delete item;
                      }
                  }
              }
              

              The question is about the else-if condition above, which is, why without delete item;, won't the item be removed from the list, please?

              A Offline
              A Offline
              Asperamanca
              wrote on 13 May 2020, 13:28 last edited by
              #6

              @tomy said in Range-based for loop for a QList:

                  for(auto& item : items)
                  {
                      list->removeItemWidget(item);
                      delete item;
                  }
              

              Not sure it's safe to delete an item while looping over the list
              Safer to do:

                      for(auto& item : items)
                      {
                          list->removeItemWidget(item);
                      }
                      qDeletAll(items);
              
              C 1 Reply Last reply 13 May 2020, 18:10
              2
              • T Offline
                T Offline
                tomy
                wrote on 13 May 2020, 16:43 last edited by tomy
                #7

                I hope I get answers for the last two questions I asked, "entirely" and "destructor". Should I make separate threads for them?

                @Bonnie
                Well, there's no widget set by setItemWidget; I used selectionItems. So you mean that function neither removes any item in the list nor is it needed in the code?

                @Asperamanca

                It may make sense not to delete the cells of the list while you're still connected to it, but except for that is there any rationale?
                So if I use this for that last condition, it's the easiest and best method!

                else if(button->text().contains("Remove")) {
                        qDeleteAll(list->selectedItems());
                
                B 1 Reply Last reply 13 May 2020, 17:00
                0
                • T tomy
                  13 May 2020, 16:43

                  I hope I get answers for the last two questions I asked, "entirely" and "destructor". Should I make separate threads for them?

                  @Bonnie
                  Well, there's no widget set by setItemWidget; I used selectionItems. So you mean that function neither removes any item in the list nor is it needed in the code?

                  @Asperamanca

                  It may make sense not to delete the cells of the list while you're still connected to it, but except for that is there any rationale?
                  So if I use this for that last condition, it's the easiest and best method!

                  else if(button->text().contains("Remove")) {
                          qDeleteAll(list->selectedItems());
                  
                  B Offline
                  B Offline
                  Bonnie
                  wrote on 13 May 2020, 17:00 last edited by
                  #8

                  @tomy Yes, if you open qlistwidget.h, you can see that:

                  inline void QListWidget::removeItemWidget(QListWidgetItem *aItem)
                  { setItemWidget(aItem, nullptr); }
                  
                  T 1 Reply Last reply 13 May 2020, 17:42
                  1
                  • B Bonnie
                    13 May 2020, 17:00

                    @tomy Yes, if you open qlistwidget.h, you can see that:

                    inline void QListWidget::removeItemWidget(QListWidgetItem *aItem)
                    { setItemWidget(aItem, nullptr); }
                    
                    T Offline
                    T Offline
                    tomy
                    wrote on 13 May 2020, 17:42 last edited by
                    #9

                    @Bonnie

                    I took a look twice on the task that removeItemWidget does, but couldn't understand this, since the setItemWidget looks complicated.
                    Will you explain what that remove function does in my code, please. This way it becomes clearer I suppose.

                    C B 2 Replies Last reply 13 May 2020, 18:11
                    0
                    • A Asperamanca
                      13 May 2020, 13:28

                      @tomy said in Range-based for loop for a QList:

                          for(auto& item : items)
                          {
                              list->removeItemWidget(item);
                              delete item;
                          }
                      

                      Not sure it's safe to delete an item while looping over the list
                      Safer to do:

                              for(auto& item : items)
                              {
                                  list->removeItemWidget(item);
                              }
                              qDeletAll(items);
                      
                      C Offline
                      C Offline
                      Christian Ehrlicher
                      Lifetime Qt Champion
                      wrote on 13 May 2020, 18:10 last edited by
                      #10

                      @Asperamanca said in Range-based for loop for a QList:

                      Safer to do:

                      In this case it's not needed - it just adds another loop for nothing.

                      Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
                      Visit the Qt Academy at https://academy.qt.io/catalog

                      A 1 Reply Last reply 14 May 2020, 03:52
                      1
                      • T tomy
                        13 May 2020, 17:42

                        @Bonnie

                        I took a look twice on the task that removeItemWidget does, but couldn't understand this, since the setItemWidget looks complicated.
                        Will you explain what that remove function does in my code, please. This way it becomes clearer I suppose.

                        C Offline
                        C Offline
                        Christian Ehrlicher
                        Lifetime Qt Champion
                        wrote on 13 May 2020, 18:11 last edited by
                        #11

                        @tomy said in Range-based for loop for a QList:

                        Will you explain what that remove function does in my code, please.

                        It removes the widget from the view, nothing more (and exactly what the function name states...)

                        Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
                        Visit the Qt Academy at https://academy.qt.io/catalog

                        T A 2 Replies Last reply 13 May 2020, 18:20
                        1
                        • C Christian Ehrlicher
                          13 May 2020, 18:11

                          @tomy said in Range-based for loop for a QList:

                          Will you explain what that remove function does in my code, please.

                          It removes the widget from the view, nothing more (and exactly what the function name states...)

                          T Offline
                          T Offline
                          tomy
                          wrote on 13 May 2020, 18:20 last edited by
                          #12

                          @Christian-Ehrlicher

                          By "from the view" you mean "disappearing" right? But it does nothing to be seen.

                          1 Reply Last reply
                          0
                          • T tomy
                            13 May 2020, 17:42

                            @Bonnie

                            I took a look twice on the task that removeItemWidget does, but couldn't understand this, since the setItemWidget looks complicated.
                            Will you explain what that remove function does in my code, please. This way it becomes clearer I suppose.

                            B Offline
                            B Offline
                            Bonnie
                            wrote on 13 May 2020, 18:24 last edited by Bonnie
                            #13

                            @tomy As I said, if you haven't called setItemWidget to set a widget, then it does nothing at all.
                            [ADDED]
                            And setItemWidget is not that complicated.
                            You can use it to set a widget to a item, maybe a button, a combox, or any kind of widget.
                            When the item is visible in the list view, the widget will be shown on the item rect.
                            So by removeItemWidget, you can remove that widget.

                            T 1 Reply Last reply 14 May 2020, 07:28
                            0
                            • C Christian Ehrlicher
                              13 May 2020, 18:11

                              @tomy said in Range-based for loop for a QList:

                              Will you explain what that remove function does in my code, please.

                              It removes the widget from the view, nothing more (and exactly what the function name states...)

                              A Offline
                              A Offline
                              Asperamanca
                              wrote on 14 May 2020, 03:52 last edited by
                              #14
                              This post is deleted!
                              1 Reply Last reply
                              0
                              • C Christian Ehrlicher
                                13 May 2020, 18:10

                                @Asperamanca said in Range-based for loop for a QList:

                                Safer to do:

                                In this case it's not needed - it just adds another loop for nothing.

                                A Offline
                                A Offline
                                Asperamanca
                                wrote on 14 May 2020, 03:52 last edited by Asperamanca
                                #15
                                This post is deleted!
                                1 Reply Last reply
                                0
                                • B Bonnie
                                  13 May 2020, 18:24

                                  @tomy As I said, if you haven't called setItemWidget to set a widget, then it does nothing at all.
                                  [ADDED]
                                  And setItemWidget is not that complicated.
                                  You can use it to set a widget to a item, maybe a button, a combox, or any kind of widget.
                                  When the item is visible in the list view, the widget will be shown on the item rect.
                                  So by removeItemWidget, you can remove that widget.

                                  T Offline
                                  T Offline
                                  tomy
                                  wrote on 14 May 2020, 07:28 last edited by tomy
                                  #16

                                  @Bonnie

                                  I've used "addItem" for both the comboBox and listWidget to add items thereby they are visible, but removeItem is for this usage apparently and deleting the selected items will do the job.
                                  Thanks.

                                  1 Reply Last reply
                                  0

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                                  13 May 2020, 10:21

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