can you please tell me the difference between the "point" and the "arrow", for example :
file.open
and
->start() (with QThread)
i thought the arrow was used for "methods", whereas the "point" is used for "attributes", but open for example is a method.
thanks for your answer
It's not just for Qt, the . is used when the variable in question is referencing the actual instance of the type/class.
Example:
QLabel label(QString("Hello"));
label.show();
The -> is used when the variable is a pointer that can hold the address of the type/class.
Example:
QLabel *label = new QLabel(QString("Hello"));
label->show();
-> is used for pointers. if x is declared as pointer to sth, x-> is used for attributes, otherwise . is used.
QLabel *label = new QLabel(tr("Heyy"));
QHBoxLayout hbox = new QHBoxLayout;
label->show();
hbox.addWidget("foo");
Related
I've experienced a weird crash when trying to find a QLineEdit in a QFormLayout.
Firstly, I created a QFormLayout and set a name for it:
QFormLayout *charColLayout = new QFormLayout; charColLayout->setObjectName("charColLayout");
Then, I created a QLineEdit, modified it a bit and add it in to the layout, and I also give it a name:
QLineEdit *delim = new QLineEdit;
delim->setMaxLength(1);
delim->setMaximumWidth(100);
delim->setText("/");
delim->setObjectName("delEdit");
charColLayout->addRow("Delimiter", delim);
Afterward, in a completely different function, I re-searched that layout with findChild():
QFormLayout *charcoal = secondHoriField->findChild<QFormLayout *>("charColLayout", Qt::FindChildrenRecursively);
It should be noted that secondHoriField is just a normal QLayout which my QFormLayout is located in.
Finally, I attempted to find that QLineEdit:
QLineEdit *delimEdit = charcoal->findChild<QLineEdit*>("delEdit", Qt::FindChildrenRecursively);
if (delimEdit == nullptr) {cerr << "error\n";} //debug
string curDelim = qStrToStr(delimEdit->text());
And it surprisingly came down with a crash, and as the output shown, it's because the delimEdit is null.
18:06:10: Starting D:\...\build-cryptog-Desktop_Qt_5_15_2_MinGW_64_bit-Debug\debug\cryptog.exe ...
error
18:06:17: The program has unexpectedly finished.
18:06:17: The process was ended forcefully.
18:06:17: D:\...\build-cryptog-Desktop_Qt_5_15_2_MinGW_64_bit-Debug\debug\cryptog.exe crashed.
But when I switched the findChild() function for this rather bruteforce-y line:
QLineEdit *delimEdit = dynamic_cast<QLineEdit*>(charcoal->itemAt(1)->widget());
cerr << qStrToStr(delimEdit->objectName()) << endl; //debug line
The program ran fine, and it showed the same name I set for the QLineEdit:
18:12:02: Starting D:\...\build-cryptog-Desktop_Qt_5_15_2_MinGW_64_bit-Debug\debug\cryptog.exe ...
delEdit
18:12:11: D:\...\build-cryptog-Desktop_Qt_5_15_2_MinGW_64_bit-Debug\debug\cryptog.exe exited with code 0
Why did this happened?
Another note: qStrToStr() is a function I implement to convert QString to std::string, and I have hand-checked it.
While findChild is a QObject method the itemAt is a QFormLayout method.
QObject::findChild
QFormLayout::itemAt
With addRow you add an item to the QFormLayout. This does not make it a child in the context of the QObject.
QFormLayout::addRow
The purpose of the QFormLayout is to organize the positioning of QWidgets, it is not meant to serve as a container. Maybe you could check whether the top level QWidget (e.g. QMainWindow) holding the QFormLayout would be a better choice as a parent for the QLineEdit.
Assuming you have some kind of QMainWindow:
QMainWindow myMainWindow;
// ...
QLineEdit *delim = new QLineEdit(&myMainWindow);
delim->setObjectName("delEdit");
//...
In another location:
auto delimEdit = myMainWindow.findChild<QLineEdit*>("delEdit");
Using Qt 5.9 on Linux, I have a QComboBox with several labels.
qc = new QComboBox;
qc->addItem(tr("Red"));
qc->addItem(tr("Green"));
qc->addItem(tr("Blue"));
Lets say a user activates the QComboBox and the 3 color labels are shown in the drop down list. The user then selects the 1st item (red).
What I want to do is have the QComboBox display a different value than what was selected. I.e., if red is selected, then a number is shown, possibly 1 for the first item (or it could be an R for Red), and if green is selected, then display 2 (or G) for the second item.
My goal in doing this is to use less display space (less wide) than is actually necessary to show the complete text of the selection because some of my item strings are quite long and a much shorter label is desired when the QComboBox is not activated in it's drop down state. Besides, the item strings are descriptive and abbreviations would work better for displaying.
Edit:
Using Marek's example, thought this might help. Here's what I have. I'm expecting if the user selects from the list, then an R, G, or a B should be displayed after.
QStandardItem *red = new QStandardItem();
red->setData(tr("Red"), Qt::DisplayRole);
red->setData("R", Qt::UserRole);
QStandardItem *green = new QStandardItem();
green->setData(tr("Green"), Qt::DisplayRole);
green->setData("G", Qt::UserRole);
QStandardItem *blue = new QStandardItem();
blue->setData(tr("Blue"), Qt::DisplayRole);
blue->setData("B", Qt::UserRole);
QStandardItemModel *rgb_model = new QStandardItemModel(this);
rgb_model->setItem(0, red);
rgb_model->setItem(1, green);
rgb_model->setItem(2, blue);
QComboBox *rgb_cb = new QComboBox();
rgb_cb->setModel(rgb_model);
I get the feeling it's because I don't quite understand how to use Qt::UserRole.
Yes it is possible. QComboBox uses data model to manage items.
You have to provide own data model, with items with respective data values.
QStandardItem *itme1 = new QStandardItem();
item1->setData(tr("Red"), Qt::DisplayRole);
item1->setData("1", Qt::UserRole); // note doesn't have to be a string.
QStandardItem *itme2 = new QStandardItem();
item2->setData(tr("Green"), Qt::DisplayRole);
item2->setData("2", Qt::UserRole);
QStandardItemModel *model = new QStandardItemModel(this);
mode->setItem(1, item1);
mode->setItem(2, item2);
qc->setModel(model);
It should work, but I didn't test it. At least this should be some clue.
Please review QComboBox documentation, especially about roles.
Another solution is use translations with multiple lengths. You can provide couple translation for a single string. Each translation should be graphically shorter than earlier one.
In such situation QString contains all possibilities separated by spatial character. When such string is rendered first substring (between separators) which will fit available space will be used.
Now I do not remember what is the separator value. I've used this very long time ago (with Qt 4.8) and now can't find reference for it.
In your example for make it short just make:
qc->setWidth( 20 );
But if you really want user choose something, then:
connect( qc, SIGNAL( onCurrentIndexChanged( int ) ), SLOT( changeComboText() ) );
[...]
void changeComboText()
{
QString shortText;
//Determine short value for shortText
qc->setCurrentText( shortText );
}
I created two QGLwidget objects:
slicerCanvas* slicerX_;
secCan* secWid_;
secWid_ = new secCan(this);
//slicerX_ load data and create texture object share with secWid_
slicerX_ = new slicerCanvas(this,secWid_);
and in the main window, I use QHBoxLayout:
hBox_ = new QHBoxLayout;
hBox_->addWidget(slicerX_);
hBox_->addWidget(secWid_);
centerWidget_->setLayout(hBox_);
It works right, but if I addWidget like this:
hBox_ = new QHBoxLayout;
hBox_->addWidget(secWid_);//first
hBox_->addWidget(slicerX_);//second
centerWidget_->setLayout(hBox_);
The secWid_ will not paint anything, only slicerX_ paints correctly. I am confused as to why.
I have a QGraphicsScene of big dimension for displaying a database content.
Part of the database is made of pictures that I place in the QGraphicsScene thanks to the method setPos() of a QGraphicsPixmapItem and this works fine with thousands of pictures.
In front of these pictures, I place QCheckboxes that are finally accessible through QGraphicsProxyWidgets. But QGraphicsProxyWidget::setPos(qreal x, qreal y) results in casting provided coordinates in signed short in the QGraphicsScene.
However, doing a QGraphicsProxyWidget::pos() returns correctly the original coordinates, even above 2^16.
Here is the code:
QCheckBox* checkbox = new QCheckBox("", this);
QWidget* dummyWidget = new QWidget; //used for having a transparent background
dummyWidget->setStyleSheet("background-color:transparent;"
"outline-color:transparent;"
"font-size: 8pt;");
QHBoxLayout* dummyLayout = new QHBoxLayout(dummyWidget);
dummyLayout->addWidget(checkbox);
QGraphicsProxyWidget* proxyWidget = scene.addWidget(dummyWidget);
proxyWidget->setPos(0, 120*i);
When 120*i is between 32769 and 65536, QChekBoxes don't show. For above values, QCheckBoxes are shown like if y = value - 65536.
I have tried many things without success, like
- proxyWidget->moveBy
- dummyWidget->move
- dummyWidget->setFixedSize(0, 240*i); checkbox->move(0, 120*i);
Any solution?
PS: The toolchain/cross-toolchain I depend from embeds QT4.8.1. for the desktop side.
I have no way to change that so upgrading to QT5.x is not an option.
You can use next trick:
void setNewPos(QGraphicsItem *item, QPointF pos)
{
item->resetTransform();
QTransform trans = item->transform();
item->setTransform(trans.translate(pos.x(), pos.y()));
}
Now, you can call this func:
QPushButton *btn = new QPushButton("Hello, people!");
QGraphicsProxyWidget *wdgItem = scene->addWidget(btn);
setNewPos(wdgItem, view->mapToScene(0,0)); // There's scenePos can have any coords
I am loading .ui files via QUiloader, and showing the GUI in my application.
QWidget *mywidget = loader.load(file, this);
QList<QWidget*> wlist = mywidget.findChildren<QWidget *>()
I would like to know what is the text on QPushbutton. I know there is a method text() to get a text from Pushbutton, but it is not accessible when I do:
QString btext = wlist.at(1).text();
Any idea how I can get the text from QPushbutton, and other Widgets, when they grouped as QWidget?
Thanks.
You should search for QPushButtons instead of QWidgets:
QList<QPushButton*> blist = widget.findChildren<QPushButton*>();
Still your code wouldn't compile. The last line should read:
QString btext = blist.at(1)->text();
Using -> since you are accessing a pointer, not the widget. Also you should check if the findChildren() function actually returnes enough buttons. You would get a crash or assertions when accessing a list item by an invalid index.
Also please note that at(1) does not return the first but the second item in the list (lists start from 0).
Update: If you search for QWidgets and cast each of them you need to take care of getting a nullptr:
QList<QWidget*> wlist = widget.findChildren<QWidget*>();
foreach (QWidget* w, wlist)
{
QPushButton* b = dynamic_cast<QPushButton*>(w);
// If "w" is not a button "b" is nullptr
if (b)
{
QString btext = b->text();
}
}