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Support for QStandardItem proxies?

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  • VRoninV VRonin

    I guess you could use a QIdentityProxyModel subclass that reimplements data() but I still think the delegate solution proposed here is the preferred way. Especially if you plan to make the data editable

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    elfring
    wrote on last edited by
    #6

    I have tried out to append a text by a QIdentityProxyModel subclass to a member variable of a custom data structure.
    Unfortunately, the display of one view from my test program indicates that the function “QVariant::canConvert” did not provide the result which I expected here.
    Would you like to clarify any affected implementation details?

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    • VRoninV Offline
      VRoninV Offline
      VRonin
      wrote on last edited by
      #7

      They try to display something and delegate edit attempts.

      I disagree, or at least it's not 100% accurate.

      Items are connected with their data models.

      Anything said above actually applies to any data model (QAbstractItemModel subclass), regardless of the implementation

      the display of one view from my test program

      can you post your code?

      "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
      ~Napoleon Bonaparte

      On a crusade to banish setIndexWidget() from the holy land of Qt

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      • VRoninV VRonin

        They try to display something and delegate edit attempts.

        I disagree, or at least it's not 100% accurate.

        Items are connected with their data models.

        Anything said above actually applies to any data model (QAbstractItemModel subclass), regardless of the implementation

        the display of one view from my test program

        can you post your code?

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        elfring
        wrote on last edited by
        #8

        can you post your code?

        • I am curious on how a code review will evolve for my test program.
        • The forum software gave me the information “Uploading 100%” and “You do not have enough privileges for this action.”.
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        • VRoninV VRonin

          They try to display something and delegate edit attempts.

          I disagree, or at least it's not 100% accurate.

          Items are connected with their data models.

          Anything said above actually applies to any data model (QAbstractItemModel subclass), regardless of the implementation

          the display of one view from my test program

          can you post your code?

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          elfring
          wrote on last edited by
          #9

          Another try for a possible code review …

          main.cpp:

          #include <QApplication>
          #include <QtUiTools/QUiLoader>
          #include <QFile>
          #include <QString>
          #include <QWidget>
          #include <QListView>
          #include <QStandardItemModel>
          #include <QIdentityProxyModel>
          #include <QMetaType>
          #include <iostream>
          #include <stdexcept>
          #include <cstdio>
          #include <cstdlib>
          
          struct my_message
          {
              QString text;
          
              my_message(char const * s = "ABC")
              : text(s)
              { }
          
              my_message(my_message const& s)
              : text(s.text)
              { }
          
              ~my_message()
              { }
          };
          Q_DECLARE_METATYPE(my_message);
          
          class my_item : public QStandardItem
          {
          public:
              my_item(my_message const mm)
              { setData(QVariant::fromValue(mm), Qt::DisplayRole); }
          };
          
          class my_proxy : public QIdentityProxyModel
          {
              QVariant data(QModelIndex const & index, int role) const override
              {
                  if (role != Qt::DisplayRole)
                      return QIdentityProxyModel::data(index, role);
          
                  auto x(sourceModel()->data(index));
                  if (x.canConvert<my_message>())
                  {
                      my_message mm(x.value<my_message>());
                      mm.text.append("||");
                      return QVariant::fromValue(mm);
                  }
                  else
                  {
                      return "***";
                  }
              }
          };
          
          struct my_views : public QWidget
          {
              Q_OBJECT
              QListView* v1;
              QListView* v2;
          
          public:
              explicit my_views(QWidget* parent = nullptr)
              : QWidget(parent)
              {
          //         QFile f(":/form.ui");
                  QFile f("/home/elfring/Projekte/view-test2/form.ui");
                  if (!f.open(QFile::ReadOnly))
                      throw std::runtime_error(tr("UI file could not be opened.").toStdString());
          
                  QUiLoader l;
                  QWidget* w = l.load(&f, this);
                  if (!w)
                      throw std::runtime_error(l.errorString().toStdString());
          
                  f.close();
          
                  v1 = findChild<QListView*>("V1");
                  if (!v1)
                      throw std::runtime_error(tr("First view was not found.").toStdString());
          
                  v2 = findChild<QListView*>("V2");
                  if (!v2)
                      throw std::runtime_error(tr("Second view was not found.").toStdString());
          
                  auto i1(new QStandardItem("abc"));
                  auto i2(new my_item("XYZ"));
                  auto m1(new QStandardItemModel);
                  auto m2(new QStandardItemModel);
                  auto mp(new my_proxy);
                  m1->appendRow(i1);
                  m2->appendRow(i2);
                  mp->setSourceModel(m2);
                  v1->setModel(m1);
                  v2->setModel(mp);
              }
          };
          
          #include "main.moc"
          
          int main(int argc, char** argv)
          {
              try
              {
                  QApplication app(argc, argv);
                  qRegisterMetaType<my_message>("my_message");
                  my_views mv;
                  mv.show();
                  return app.exec();
              }
              catch (std::bad_alloc const& b)
              {
                  (void) std::fputs("out of memory\n", stderr);
                  return EXIT_FAILURE;
              }
              catch (std::exception const& x)
              {
                  (void) std::fprintf(stderr, "A kind of standard%s\n%s\n", " exception was caught.", x.what());
                  return EXIT_FAILURE;
              }
              catch (...)
              {
                  (void) std::fprintf(stderr, "An unknown%s\n", " exception was caught.");
                  throw;
              }
          }
          

          CMakeLists.txt:

          cmake_minimum_required(VERSION 3.1)
          project(view-test CXX)
          set(CMAKE_AUTOMOC ON)
          find_package(Qt5 COMPONENTS Core Widgets UiTools REQUIRED)
          include_directories(${Qt5Widgets_INCLUDE_DIRS} ${Qt5Core_INCLUDE_DIRS} ${Qt5UiTools_INCLUDE_DIRS})
          add_executable(test1 main.cpp)
          target_link_libraries(test1 Qt5::Widgets Qt5::Core Qt5::UiTools)
          

          form.ui:

          <?xml version="1.0" encoding="UTF-8"?>
          <ui version="4.0">
           <class>my_views</class>
           <widget class="QWidget" name="my_views">
            <property name="geometry">
             <rect>
              <x>0</x>
              <y>0</y>
              <width>282</width>
              <height>228</height>
             </rect>
            </property>
            <property name="windowTitle">
             <string>Display test</string>
            </property>
            <widget class="QListView" name="V1">
             <property name="geometry">
              <rect>
               <x>10</x>
               <y>10</y>
               <width>256</width>
               <height>91</height>
              </rect>
             </property>
             <property name="uniformItemSizes">
              <bool>true</bool>
             </property>
            </widget>
            <widget class="Line" name="L1">
             <property name="geometry">
              <rect>
               <x>10</x>
               <y>100</y>
               <width>241</width>
               <height>20</height>
              </rect>
             </property>
             <property name="lineWidth">
              <number>9</number>
             </property>
             <property name="orientation">
              <enum>Qt::Horizontal</enum>
             </property>
            </widget>
            <widget class="QListView" name="V2">
             <property name="geometry">
              <rect>
               <x>10</x>
               <y>120</y>
               <width>256</width>
               <height>91</height>
              </rect>
             </property>
             <property name="uniformItemSizes">
              <bool>true</bool>
             </property>
            </widget>
           </widget>
           <resources/>
           <connections/>
          </ui>
          
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          • VRoninV Offline
            VRoninV Offline
            VRonin
            wrote on last edited by
            #10
            1. does if (x.canConvert<my_message>()) return false?
            2. what is your intention in this code snippet?
            my_message mm(x.value<my_message>());
            mm.text.append("||");
            return QVariant::fromValue(mm);
            
            1. You are leaking all 3 of the models. The view does not own the model

            "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
            ~Napoleon Bonaparte

            On a crusade to banish setIndexWidget() from the holy land of Qt

            E 2 Replies Last reply
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            • VRoninV VRonin
              1. does if (x.canConvert<my_message>()) return false?
              2. what is your intention in this code snippet?
              my_message mm(x.value<my_message>());
              mm.text.append("||");
              return QVariant::fromValue(mm);
              
              1. You are leaking all 3 of the models. The view does not own the model
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              elfring
              wrote on last edited by
              #11

              does if (x.canConvert<my_message>()) return false?

              I get this impression after I see three asterisks in the display from my test widget on the screen.

              what is your intention in this code snippet?

              I am trying also to get more familiar with the provided programming interfaces around models and views.

              You are leaking all 3 of the models.

              I do not really need my own clean-up for this software experiment at the moment.

              The view does not own the model

              Thanks for your reminder.

              Do you spot any other suspicious implementation details?

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              • VRoninV VRonin
                1. does if (x.canConvert<my_message>()) return false?
                2. what is your intention in this code snippet?
                my_message mm(x.value<my_message>());
                mm.text.append("||");
                return QVariant::fromValue(mm);
                
                1. You are leaking all 3 of the models. The view does not own the model
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                elfring
                wrote on last edited by
                #12

                does `if (x.canConvert<my_message>()) return false?

                I have added a test output for my local variable “x”. The programming interface “qDebug()” provides the information “QVariant(Invalid)” then so far.

                • Would you like to help with finding an explanation for this software behaviour?
                • How can a source model work here?
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                • Christian EhrlicherC Offline
                  Christian EhrlicherC Offline
                  Christian Ehrlicher
                  Lifetime Qt Champion
                  wrote on last edited by
                  #13

                  @elfring said in Support for QStandardItem proxies?:

                  auto x(sourceModel()->data(index));

                  How should this work at all? http://doc.qt.io/qt-5/qidentityproxymodel.html#mapToSource

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

                  VRoninV 1 Reply Last reply
                  1
                  • Christian EhrlicherC Christian Ehrlicher

                    @elfring said in Support for QStandardItem proxies?:

                    auto x(sourceModel()->data(index));

                    How should this work at all? http://doc.qt.io/qt-5/qidentityproxymodel.html#mapToSource

                    VRoninV Offline
                    VRoninV Offline
                    VRonin
                    wrote on last edited by
                    #14

                    Good spot, I'm surprised it didn't just assert. I got shouted at in code review for having models that didn't assert when index.model()!=this

                    @elfring replace auto x(sourceModel()->data(index)); with auto x=QIdentityProxyModel::data(index, role);

                    "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                    ~Napoleon Bonaparte

                    On a crusade to banish setIndexWidget() from the holy land of Qt

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                    • Christian EhrlicherC Offline
                      Christian EhrlicherC Offline
                      Christian Ehrlicher
                      Lifetime Qt Champion
                      wrote on last edited by
                      #15

                      @VRonin said in Support for QStandardItem proxies?:

                      I'm surprised it didn't just assert

                      Maybe because Qt was not compiled in debug mode. Or there is no assert and the new index check stuff is not yet used there - feel free to add it ;)

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

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                      • VRoninV VRonin

                        Good spot, I'm surprised it didn't just assert. I got shouted at in code review for having models that didn't assert when index.model()!=this

                        @elfring replace auto x(sourceModel()->data(index)); with auto x=QIdentityProxyModel::data(index, role);

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                        elfring
                        wrote on last edited by
                        #16

                        replace auto x(sourceModel()->data(index)); with auto x=QIdentityProxyModel::data(index, role);

                        Thanks for this suggestion.

                        • Unfortunately, I selected a questionable member function call combination before.
                        • The test case is working as expected together with the statement “return mm.text;” now.
                        1 Reply Last reply
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                        • VRoninV VRonin

                          Good spot, I'm surprised it didn't just assert. I got shouted at in code review for having models that didn't assert when index.model()!=this

                          @elfring replace auto x(sourceModel()->data(index)); with auto x=QIdentityProxyModel::data(index, role);

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                          elfring
                          wrote on last edited by
                          #17

                          Good spot, I'm surprised it didn't just assert.

                          • Did I try the usage of model indexes out in appropriate way for my test case?
                          • Do indexes need to be different for proxy and source models?
                          VRoninV 1 Reply Last reply
                          0
                          • E elfring

                            Good spot, I'm surprised it didn't just assert.

                            • Did I try the usage of model indexes out in appropriate way for my test case?
                            • Do indexes need to be different for proxy and source models?
                            VRoninV Offline
                            VRoninV Offline
                            VRonin
                            wrote on last edited by
                            #18

                            @elfring said in Support for QStandardItem proxies?:

                            Did I try the usage of model indexes out in appropriate way for my test case?

                            Usually you'd want a Q_ASSERT that uses checkIndex()

                            Do indexes need to be different for proxy and source models?

                            Yes, obviously

                            "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                            ~Napoleon Bonaparte

                            On a crusade to banish setIndexWidget() from the holy land of Qt

                            E 1 Reply Last reply
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                            • VRoninV VRonin

                              @elfring said in Support for QStandardItem proxies?:

                              Did I try the usage of model indexes out in appropriate way for my test case?

                              Usually you'd want a Q_ASSERT that uses checkIndex()

                              Do indexes need to be different for proxy and source models?

                              Yes, obviously

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                              elfring
                              wrote on last edited by
                              #19

                              Yes, obviously

                              • Should the difference between indexes for proxy and source models be better described in the Qt documentation?
                              • How do you think about the introduction of a class like QProxyModelIndex then?
                              VRoninV 1 Reply Last reply
                              0
                              • E elfring

                                Yes, obviously

                                • Should the difference between indexes for proxy and source models be better described in the Qt documentation?
                                • How do you think about the introduction of a class like QProxyModelIndex then?
                                VRoninV Offline
                                VRoninV Offline
                                VRonin
                                wrote on last edited by
                                #20

                                @elfring said in Support for QStandardItem proxies?:

                                How do you think about the introduction of a class like QProxyModelIndex then?

                                QAbstractPorxyModel::mapToSource/QAbstractPorxyModel::mapFromSource already do everything that class would do so I see no gain in introducing it

                                Should the difference between indexes for proxy and source models be better described in the Qt documentation?

                                A proxy model is still a model, the docs say "Note that it's undefined behavior to pass illegal indices to item models" so I feel it is documented already

                                "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                                ~Napoleon Bonaparte

                                On a crusade to banish setIndexWidget() from the holy land of Qt

                                E 1 Reply Last reply
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                                • VRoninV VRonin

                                  @elfring said in Support for QStandardItem proxies?:

                                  How do you think about the introduction of a class like QProxyModelIndex then?

                                  QAbstractPorxyModel::mapToSource/QAbstractPorxyModel::mapFromSource already do everything that class would do so I see no gain in introducing it

                                  Should the difference between indexes for proxy and source models be better described in the Qt documentation?

                                  A proxy model is still a model, the docs say "Note that it's undefined behavior to pass illegal indices to item models" so I feel it is documented already

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                                  elfring
                                  wrote on last edited by
                                  #21

                                  A proxy model is still a model,

                                  This information is generally appropriate.

                                  the docs say "Note that it's undefined behavior to pass illegal indices to item models"

                                  A constraint is mentioned.

                                  so I feel it is documented already

                                  Now I imagine that a better class design can prevent the passing of inappropriate indexes a bit more.
                                  How are the chances to specify that QAbstractProxyModel-like objects need to work with QProxyModelIndex objects instead?

                                  VRoninV 1 Reply Last reply
                                  0
                                  • E elfring

                                    A proxy model is still a model,

                                    This information is generally appropriate.

                                    the docs say "Note that it's undefined behavior to pass illegal indices to item models"

                                    A constraint is mentioned.

                                    so I feel it is documented already

                                    Now I imagine that a better class design can prevent the passing of inappropriate indexes a bit more.
                                    How are the chances to specify that QAbstractProxyModel-like objects need to work with QProxyModelIndex objects instead?

                                    VRoninV Offline
                                    VRoninV Offline
                                    VRonin
                                    wrote on last edited by VRonin
                                    #22

                                    @elfring said in Support for QStandardItem proxies?:

                                    Now I imagine that a better class design can prevent the passing of inappropriate indexes a bit more.

                                    Agree that's why I said:

                                    I'm surprised it didn't just assert.

                                    How are the chances to specify that QAbstractProxyModel-like objects need to work with QProxyModelIndex objects instead?

                                    1. QAbstractProxyModel is a subclass of QAbstractItemModel and the view should not care whether the model it's attached to is a proxy or not

                                    "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                                    ~Napoleon Bonaparte

                                    On a crusade to banish setIndexWidget() from the holy land of Qt

                                    E 1 Reply Last reply
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                                    • VRoninV VRonin

                                      @elfring said in Support for QStandardItem proxies?:

                                      Now I imagine that a better class design can prevent the passing of inappropriate indexes a bit more.

                                      Agree that's why I said:

                                      I'm surprised it didn't just assert.

                                      How are the chances to specify that QAbstractProxyModel-like objects need to work with QProxyModelIndex objects instead?

                                      1. QAbstractProxyModel is a subclass of QAbstractItemModel and the view should not care whether the model it's attached to is a proxy or not
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                                      elfring
                                      wrote on last edited by
                                      #23

                                      the view should not care whether the model it's attached to is a proxy or not

                                      Can overloaded functions (from a specific proxy class) help any more to detect questionable indexes?

                                      VRoninV 1 Reply Last reply
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                                      • E elfring

                                        the view should not care whether the model it's attached to is a proxy or not

                                        Can overloaded functions (from a specific proxy class) help any more to detect questionable indexes?

                                        VRoninV Offline
                                        VRoninV Offline
                                        VRonin
                                        wrote on last edited by
                                        #24

                                        @elfring said in Support for QStandardItem proxies?:

                                        Can overloaded functions (from a specific proxy class) help any more to detect questionable indexes?

                                        It can help but there's no bullet proof solution.

                                        In the meantime I submitted a change to QStandardItemModel that would have made your bug assert in debug

                                        "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                                        ~Napoleon Bonaparte

                                        On a crusade to banish setIndexWidget() from the holy land of Qt

                                        E Christian EhrlicherC 2 Replies Last reply
                                        1
                                        • VRoninV VRonin

                                          @elfring said in Support for QStandardItem proxies?:

                                          Can overloaded functions (from a specific proxy class) help any more to detect questionable indexes?

                                          It can help but there's no bullet proof solution.

                                          In the meantime I submitted a change to QStandardItemModel that would have made your bug assert in debug

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                                          E Offline
                                          elfring
                                          wrote on last edited by
                                          #25

                                          In the meantime I submitted a change to QStandardItemModel that would have made your bug assert in debug

                                          I find it interesting that my clarification request triggered such a software evolution finally.
                                          Would you like to continue the development discussion also around proxies for QStandardItem (or eventually other classes)?

                                          1 Reply Last reply
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