I was reading MVC tutorial and wanted to try out the code, but for some reason (which I'm not able to figure out) it is not working.
This code is suppose to show contents of current directory in QListWidget.
#include <QApplication>
#include <QFileSystemModel>
#include <QModelIndex>
#include <QListWidget>
#include <QListView>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QFileSystemModel *model = new QFileSystemModel;
QString dir = QDir::currentPath();
model->setRootPath(dir);
QModelIndex parentIndex = model->index(dir);
int numRows = model->rowCount(parentIndex);
QListWidget *list = new QListWidget;
QListWidgetItem *newItem = new QListWidgetItem;
for(int row = 0; row < numRows; ++row) {
QModelIndex index = model->index(row, 0, parentIndex);
QString text = model->data(index, Qt::DisplayRole).toString();
newItem->setText(text);
list->insertItem(row, newItem);
}
list->show();
return a.exec();
}
There are 2 problems.
The first described by Frank Osterfeld's answer. Move:
QListWidgetItem *newItem = new QListWidgetItem;
into your loop.
The second has to do with QFileSystemModel's threading model. from the docs for QFileSystemModel:
Unlike the QDirModel, QFileSystemModel uses a separate thread to populate itself so it will not cause the main thread to hang as the file system is being queried. Calls to rowCount() will return 0 until the model populates a directory.
and
Note: QFileSystemModel requires an instance of a GUI application.
I don't think QFileSystemModel() will work properly until after the Qt event loop is running (which is started by a.exec() in your example).
In your case, model->rowCount(parentIndex) returns 0, even though there are items in the directory (at least that's what it's doing on my test).
Replacing QFileSystemModel with QDirModel (and removing the model->setRootPath(dir) call, which QDirModel` doesn't support) populates the list.
You must create a new item for each row. Move
QListWidgetItem *newItem = new QListWidgetItem;
into the for loop.
Related
I have two QComboBoxes to connect with each other.
In particular, I'd like that if a scaling is made in the first QComboBox, this is not also shown in the second QComboBox and vice versa..
This is my code:
auto lingua_originaleT = new QComboBox();
lingua_originaleT->addItems({"Italiano", "Inglese", "Francese", "Spagnolo", "Portoghese", "Tedesco", "Cinese"});
auto lingua_targetT = new QComboBox();
lingua_targetT->addItems({"Italiano", "Inglese", "Francese", "Spagnolo", "Portoghese", "Tedesco", "Cinese"});
The result should be like this:
The same language should not appear in the second drop-down menu as well
One possible solution is to use QSortFilterProxyModel to do the filtering:
#include <QApplication>
#include <QComboBox>
#include <QHBoxLayout>
#include <QSortFilterProxyModel>
#include <QStandardItemModel>
#include <QWidget>
class FilterProxyModel: public QSortFilterProxyModel{
public:
using QSortFilterProxyModel::QSortFilterProxyModel;
protected:
bool filterAcceptsRow(int source_row, const QModelIndex &source_parent) const{
if(filterRegExp().isEmpty())
return true;
return !QSortFilterProxyModel::filterAcceptsRow(source_row, source_parent);
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QWidget widget;
widget.resize(640, 480);
widget.show();
QStandardItemModel *model = new QStandardItemModel(&widget);
const QStringList values{"Italiano", "Inglese", "Francese", "Spagnolo", "Portoghese", "Tedesco", "Cinese"};
for(const QString & value: values){
model->appendRow(new QStandardItem(value));
}
QComboBox *lingua_originaleT = new QComboBox;
FilterProxyModel *proxy_originalT = new FilterProxyModel(&widget);
proxy_originalT->setSourceModel(model);
lingua_originaleT->setModel(proxy_originalT);
QComboBox *lingua_targetT = new QComboBox;
FilterProxyModel *proxy_targetT = new FilterProxyModel(&widget);
proxy_targetT->setSourceModel(model);
lingua_targetT->setModel(proxy_targetT);
QHBoxLayout *lay = new QHBoxLayout(&widget);
lay->addWidget(lingua_originaleT);
lay->addWidget(lingua_targetT);
QObject::connect(lingua_originaleT, &QComboBox::currentTextChanged, proxy_targetT, &FilterProxyModel::setFilterFixedString);
QObject::connect(lingua_targetT, &QComboBox::currentTextChanged, proxy_originalT, &FilterProxyModel::setFilterFixedString);
lingua_originaleT->setCurrentIndex(0);
lingua_targetT->setCurrentIndex(1);
return a.exec();
}
Internally, QCombobox uses QStandardItemModel - unless you provided a custom one using setModel().
That means you can do things like:
// Just some setup
auto combo = new QComboBox(this);
combo->addItems({ "Item0", "Item1", "Item2" });
// Here is the interesting bit
auto model = qobject_cast<QStandardItemModel*>(combo->model());
auto item = model->item(0); // <-- index in the combobox
item->setEnabled(false); // <-- You can't select it anymore
if(combo->currentIndex() == 0) // Choose another one if it's already selected
combo->setCurrentIndex(1);
// From now, Item 0 will be visible in the dropdown but not selectable by the user.
I leave you find a way to get the 2 boxes disabling each other items (And importantly, enabling them back once if the selection change). This is a matter of listening the index changed signals of each boxes and and updating the other model accordingly.
I solved and the solution works perfectly!
Here's how I did it:
lingua_originaleT = new QComboBox();
lingua_targetT = new QComboBox();
QStringList traduzioneLangList = {"Italiano", "Inglese", "Francese", "Spagnolo", "Portoghese", "Tedesco", "Cinese"};
lingua_originaleT->clear();
lingua_originaleT->addItems(traduzioneLangList);
lingua_originaleT->setCurrentIndex(-1);
lingua_targetT->clear();
lingua_targetT->addItems(traduzioneLangList);
lingua_targetT->setCurrentIndex(-1);
connect(lingua_originaleT, &QComboBox::currentTextChanged, lingua_targetT, [=](const QString &selection) {
auto tarLangList = traduzioneLangList;
lingua_targetT->blockSignals(true);
tarLangList.removeOne(selection);
lingua_targetT->clear();
lingua_targetT->addItems(traduzioneLangList);
lingua_targetT->blockSignals(false);
});
connect(lingua_targetT, &QComboBox::currentTextChanged, lingua_originaleT, [=](const QString &selection) {
auto tarLangList = traduzioneLangList;
lingua_originaleT->blockSignals(true);
tarLangList.removeOne(selection);
lingua_originaleT->clear();
lingua_originaleT->addItems(traduzioneLangList);
lingua_originaleT->blockSignals(false);
});
lingua_originaleT->setCurrentIndex(0);
Many thanks to #lifof on reddit!
In Qt, QModelIndex is used to represent an index to my understanding. Officially:
This class is used as an index into item models derived from
QAbstractItemModel. The index is used by item views, delegates, and
selection models to locate an item in the model.
But I see it being used to represent a parent object. For instance, if I want to get an index in a QFileSystemModel object, I need a row, column and a parent:
QModelIndex QFileSystemModel::index(int row, int column, const QModelIndex &parent = QModelIndex()) const
I am trying to get a QModelIndex object, but to do that, I need another QModelIndex object? I am merely trying to iterate over the model. I don't have a separate parent object. How do I just create an index from row/column number? I don't understand the role of QModelIndex as a "parent". Shouldn't the model itself know what the parent object is? We passed a pointer to the constructor when creating the model.
Here's a bit of code showing the problem:
#include "MainWindow.hpp"
#include "ui_MainWindow.h"
#include <QFileSystemModel>
#include <QDebug>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
auto* model = new QFileSystemModel{ui->listView};
ui->listView->setModel(model);
ui->listView->setRootIndex(model->setRootPath("C:\\Program Files"));
connect(ui->pushButton, &QPushButton::clicked, [this] {
auto* model = static_cast<QFileSystemModel*>(ui->listView->model());
int row_count = model->rowCount();
for (int i = 0; i != row_count; ++i) {
qDebug() << model->fileName(model->index(i, 0)) << '\n';
}
});
}
Here I have a QListView object (*listView) and a QFileSystemModel object (*model). I would like to iterate over the model and do something, like print the names of the files. The output is
C:
No matter which directory the rootpath is. I assume that is because I did't pass anything as the parent.
You're just accessing the children of the root of the QFileSystemModel when you default the parent node to QModelIndex() in the call model->index(i, 0).
If you also want to list the children of those items, we'll want to iterate them, too:
#include <QApplication>
#include <QDebug>
#include <QFileSystemModel>
void list_files(const QFileSystemModel *model, QModelIndex ix = {},
QString indent = {})
{
auto const row_count = model->rowCount(ix);
for (int i = 0; i < row_count; ++i) {
auto const child = model->index(i, 0, ix);
qDebug() << qPrintable(indent) << model->fileName(child);
list_files(model, child, indent + " ");
}
}
int main(int argc, char **argv)
{
QApplication app(argc, argv);
QFileSystemModel model;
model.setRootPath(".");
list_files(&model);
}
See how we pass the child index as the new parent when we recurse into list_files()?
Note that the model is likely incomplete at this stage, as it implements lazy reading - so don't expect to see all your files with this simple program.
I am trying to connect row selections from two QTableWidget.
I mean, when I select one row in Table 1, I want my program selects the same row in table 2. The two table dont have the same number of column so I cannot just select one item for the first and select the same item on the second able.
I have tried to use the following without success:
connect(ui->table1->selectionModel(), SIGNAL(currentRowChanged(QModelIndex, QModelIndex)), ui->table2->selectionModel(), SLOT(setCurrentIndex(QModelIndex)));
It is written:
QObject::connect: No such slot QItemSelectionModel::setCurrentIndex(QModelIndex)
Do you know what is going wrong?
The problem is caused because setCurrentIndex() has two parameters, and not just one, plus the signatures do not match. So in these cases you should use a lambda and use selectRow():
#include <QApplication>
#include <QHBoxLayout>
#include <QTableWidget>
#include <QItemSelectionModel>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
auto *table1 = new QTableWidget(4, 3);
table1->setSelectionBehavior(QAbstractItemView::SelectRows);
auto table2 = new QTableWidget(4, 4);
table2->setSelectionBehavior(QAbstractItemView::SelectRows);
QObject::connect(table1->selectionModel(), &QItemSelectionModel::currentRowChanged,
[table2](const QModelIndex ¤t, const QModelIndex & previous)
{
if(previous.isValid())
table2->selectRow(current.row());
});
QWidget w;
auto lay = new QHBoxLayout(&w);
lay->addWidget(table1);
lay->addWidget(table2);
w.show();
return a.exec();
}
I am trying to create pop-up menu depending on a variable as follows:
QMenu menu(widget);
for(int i = 1; i <= kmean.getK(); i++)
{
stringstream ss;
ss << i;
string str = ss.str();
string i_str = "Merge with " + str;
QString i_Qstr = QString::fromStdString(i_str);
menu.addAction(i_Qstr, this, SLOT(mergeWith1()));
}
menu.exec(position);
where:
kmean.get(K) returns an int value,
mergeWith1() is some `SLOT()` which works fine
Issue:
The loop creates an action on menu only for i=1 case, and ignores other values of i.
Additional information
When doing the same loop with casual int values (without convert) everything works fine. e.g. if I do in loop only menu.addAction(i, this, SLOT(...))) and my K=4, a menu will be created with four actions in it, named 1, 2, 3, 4 correspondingly.
What can be the problem caused by
I think the issue is in convert part, when I convert i to string using stringstream and after to QString. May be the value is somehow lost. I am not sure.
QESTION:
How to make the loop accept the convert part?
What do I do wrong in convert part?
In Qt code, you shouldn't be using std::stringstream or std::string. It's pointless.
You have a crashing bug by having the menu on the stack and giving it a parent. It'll be double-destructed.
Don't use the synchronous blocking methods like exec(). Show the menu asynchronously using popup().
In order to react to the actions, connect a slot to the menu's triggered(QAction*) signal. That way you can deal with arbitrary number of automatically generated actions.
You can use the Qt property system to mark actions with custom attributes. QAction is a QObject after all, with all the benefits. For example, you can store your index in an "index" property. It's a dynamic property, created on the fly.
Here's a complete example of how to do it.
main.cpp
#include <QApplication>
#include <QAction>
#include <QMenu>
#include <QDebug>
#include <QPushButton>
struct KMean {
int getK() const { return 3; }
};
class Widget : public QPushButton
{
Q_OBJECT
KMean kmean;
Q_SLOT void triggered(QAction* an) {
const QVariant index(an->property("index"));
if (!index.isValid()) return;
const int i = index.toInt();
setText(QString("Clicked %1").arg(i));
}
Q_SLOT void on_clicked() {
QMenu * menu = new QMenu();
int last = kmean.getK();
for(int i = 1; i <= last; i++)
{
QAction * action = new QAction(QString("Merge with %1").arg(i), menu);
action->setProperty("index", i);
menu->addAction(action);
}
connect(menu, SIGNAL(triggered(QAction*)), SLOT(triggered(QAction*)));
menu->popup(mapToGlobal(rect().bottomRight()));
}
public:
Widget(QWidget *parent = 0) : QPushButton("Show Menu ...", parent) {
connect(this, SIGNAL(clicked()), SLOT(on_clicked()));
}
};
int main (int argc, char **argv)
{
QApplication app(argc, argv);
Widget w;
w.show();
return app.exec();
}
#include "main.moc"
Pretty simple task but I didn't manage to find anything useful in documentation. I want a QTreeView to contain a single column called "Files" with data from QFileSystemView. Here's what I've got:
QFileSystemModel *projectFiles = new QFileSystemModel();
projectFiles->setRootPath(QDir::currentPath());
ui->filesTree->setModel(projectFiles);
ui->filesTree->setRootIndex(projectFiles->index(QDir::currentPath()));
// hide all but first column
for (int i = 3; i > 0; --i)
{
ui->filesTree->hideColumn(i);
}
That gives me a single column with "Name" header. How do I rename this header?
QAbstractItemModel::setHeaderData() should work. If not, you can always inherit from QFileSystemModel and override headerData().
Quick but a little dirty trick (please note w.hideColumn()):
#include <QApplication>
#include <QFileSystemModel>
#include <QTreeView>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QTreeView w;
QFileSystemModel m;
m.setFilter(QDir::Dirs | QDir::NoDotAndDotDot);
m.setRootPath("C:\\");
w.setModel(&m);
w.setRootIndex(m.index(m.rootPath()));
w.hideColumn(3);
w.hideColumn(2);
w.hideColumn(1);
w.show();
return a.exec();
}
You can subclass QFileSystemModel and overide method headerData(). For example, if you want only to change first header label and leave the rest with their original values, you can do:
QVariant MyFileSystemModel::headerData(int section, Qt::Orientation orientation, int role) const {
if ((section == 0) && (role == Qt::DisplayRole)) {
return "Folder";
} else {
return QFileSystemModel::headerData(section,orientation,role);
}
}