如何响应 QStringListModel 的 QT 列表视图中的内部移动

Question

My app is almost done. I'm stuck trying to update elements of my mainwindow when I move an item up or down in a simple listview model that has a QStringListModel as its backend.

Here is my model for allowing drag/drop:

#ifndef MYMODEL_H
#define MYMODEL_H

#include <QStringListModel>

class mymodel : public QStringListModel
{
public:
    mymodel(QObject * parent = nullptr);
    Qt::ItemFlags flags(const QModelIndex &index) const;
};
#endif // MYMODEL_H

The model implementation is:

#include "mymodel.h"

mymodel::mymodel(QObject *parent) : QStringListModel (parent) {}

Qt::ItemFlags mymodel::flags(const QModelIndex &index) const
{
    Qt::ItemFlags defaultFlags = QStringListModel::flags(index);

    if (index.isValid())
    {
        return  Qt::ItemIsSelectable | Qt::ItemIsDragEnabled |
                Qt::ItemIsEnabled ;
    }
    else
    {
        return  Qt::ItemIsSelectable  | Qt::ItemIsDragEnabled |
                Qt::ItemIsDropEnabled | defaultFlags;
    }
}

Here is my implementation, which does work, except I cannot detect if I move a row up down.

    //create model
    model = new mymodel(this);

    //make some data
    QStringList List;
    List << "one" << "two" << "three";

   // populate the model
    model->setStringList(List);

    // create a list view
     QListView *lv = new QListView(this);

    // glue model and view together
    lv->setModel(model);

    // allow modifying the data in Listview
    lv->setDragDropMode(QAbstractItemView::InternalMove);
    lv->setDragDropOverwriteMode(false);
    lv->setEditTriggers(QAbstractItemView::AnyKeyPressed |
                        QAbstractItemView::DoubleClicked);

I've tried all of the following, they do compile, but don't do anything.

They are supposed to simply console print 'something happened', but they don't.

    // doesnt do anything! compiles
    connect(lv, &QListView::indexesMoved,
            this, &MainWindow::rowsMoved);

    // doesnt do anything! compiles
    connect(lv->model(), &QStringListModel::rowsMoved,
            this, &MainWindow::rowsMoved);

    // doesnt do anything! compiles
    connect(lv->model(), &QAbstractItemModel::rowsMoved,
            this, &MainWindow::rowsMoved);

The rowsMoved is declared in the headers with:

void rowsMoved(const QModelIndex &parent, int start, int end, const QModelIndex &destination, int row);
};

In the interim, I have found that adding to constructor:

lv->installEventFilter(this);

In the cpp as well as later defined as:

bool MainWindow::eventFilter(QObject *object, QEvent *event)
{
    if (object == lv)
    {
        if (event->type() == QEvent::ChildRemoved) {
            qDebug() << "drop event!";

        // iterate over the listview and print out it's data,
        // so if you wanted this back in your stringlist.. this is
        // where you'd do it:
        for (int i = 0; i < model->rowCount(); ++i)
        {
            qDebug().noquote() <<  model->index(i, 0).data(Qt::DisplayRole).toString();
        }
        return true;
        }
    }
    return false;
}

This gets me a 'poor mans notification' but it feels 'dirty'

Answer 1

So grateful that eyllanesc helped me! Thank you.

Posting this here, should any one need.

This code indeed does allow me edit items, move them up/down in the list view, and be notified when something in the list is changed by the user. In addition, not shown below, the below allows drag / drop operations from file manager which for my app I need.

If you were to compare my original post based on QStringListModel you'll notice they look almost exactly the same. I am still perplexed why using that model did not work. But facts are facts, this works and the other does not.

mymodel.h

#ifndef MYMODEL_H
#define MYMODEL_H

#include <QStandardItemModel>
class mymodel : public QStandardItemModel
{

public:
    mymodel(QObject * parent = nullptr);
    Qt::ItemFlags flags(const QModelIndex &index) const;
};

#endif // MYMODEL_H

mymodel.cpp

#include "mymodel.h"
#include <QDebug>

mymodel::mymodel(QObject *parent) : QStandardItemModel (parent) {}

Qt::ItemFlags mymodel::flags(const QModelIndex &index) const
{
    Qt::ItemFlags defaultFlags = QStandardItemModel::flags(index);

    if (index.isValid())
    {
        return  Qt::ItemIsSelectable | Qt::ItemIsDragEnabled |
                Qt::ItemIsEnabled    | Qt::ItemIsEditable;
    }
    else
    {
        return  Qt::ItemIsSelectable  | Qt::ItemIsDragEnabled |
                Qt::ItemIsDropEnabled | defaultFlags;
    }
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QListView>
#include <QStandardItemModel>
#include <QStringList>

class MainWindow : public QWidget
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
    QListView *lv;
    QStringList list;
    QStandardItemModel *model;

private slots:
    void itemChanged();
};
#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QBoxLayout>
#include <QDebug>
#include "mymodel.h"

MainWindow::MainWindow(QWidget *parent)
{
    lv = new QListView(this);
    model = new mymodel(lv);

    list << "one" << "two" << "three";
    for (int i=0; i < list.length(); ++i)
    {
        model->appendRow(new QStandardItem(list[i]));
    }

    lv->setModel(model);
    lv->setDragDropMode(QAbstractItemView::InternalMove);
    lv->setDragDropOverwriteMode(false);
    QBoxLayout *lo = new QBoxLayout(QBoxLayout::LeftToRight);
    lo->addWidget(lv);
    setLayout(lo);

    connect(model, &QStandardItemModel::itemChanged,
            this,  &MainWindow::itemChanged);
}

MainWindow::~MainWindow()
{
}

void MainWindow::itemChanged()
{
    qDebug().noquote() << "an item changed";
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QListView>
#include <QStandardItemModel>
#include <QStringList>

class MainWindow : public QWidget
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
    QListView *lv;
    QStringList list;
    QStandardItemModel *model;

private slots:
    void itemChanged();
};
#endif // MAINWINDOW_H