I have a scenario where I am asking the user for a number between 1 and 10 and creating that number of buttons of the type QPushButton. I then want to create a function such that when I click the button the number on the button gets printed.
Just use a lambda function like this:
for (int i = 1; i < numButtons; i++)
{
QPushButton *btn = new QPushButton(...);
connect(btn, &QPushButton::clicked, [=]() {
// Do something with 'i'
}
}
Related
I am creating a checkers board as part of a university assignment. There has been very little teaching around the GUI side of things. So I may have overcomplicated this project a bit and become stuck while trying to access the clicks from the board GUI.
I have read about lambda's in the documentation https://doc.qt.io/qt-5/qsignalmapper.html for signal mappers, but, I am not sure if it is right for the application I am coding. I have tried to implement the signal mapping so that when a particular button is pushed on the checker's board, the slot can identify it with its unique signal.
If there is a better way, or if lambdas are the best way, could you please explain how to implement this?
At the moment, my current code can't access the clicks made. I also get an error for the connect() function:
no known conversion from 'void QAbstractButton::* (bool)' to 'const char*' for the second argument.
connect(&checkers[i], &QPushButton::clicked, signalMapper, &QSignalMapper::map);
However, this compiles but does not work:
connect(&checkers[i], SIGNAL(clicked), signalMapper, SLOT(map));
Below is more complete code for greater context.
Constructor and board set function:
// Constructor
GameWindow::GameWindow(QWidget *parent):
QDialog(parent), ui(new Ui::GameWindow)
{
ui->setupUi(this);
BoardSetup(4);
}
/* Sets up the initial gameboard display with the other game information displays also being
* initialised. The game board is an array of QpushButtons that have there Icon
* changed according to where the pieces are on the board.
* Called by the GameWindow Constructor*/
void GameWindow::BoardSetup(int size)
{
{
QSignalMapper *signalMapper = new QSignalMapper(this->checkers);
connect(signalMapper, &QSignalMapper::mappedInt, this, &GameWindow::SquareClicked );
bool col=1;
for (int j=0;j<size;j++)
{
col=!col;
for(int i=0; i<size; i++)
{
if(col == 1) // logically check to see what Color the square needs to be.
{
checkers[i+j*size].setGeometry(QRect(width/size*j,width/size*i,width/size,width/size));
checkers[i+j*size].setFixedSize(QSize(width/size,width/size));
checkers[i+j*size].setStyleSheet("background-color: black");
}
else if(col==0)
{
checkers[i+j*size].setGeometry(QRect(width/size*j,width/size*i,width/size,width/size));
checkers[i+j*size].setFixedSize(QSize(width/size,width/size));
checkers[i+j*size].setStyleSheet("background-color: white");
}
col=!col;
signalMapper->setMapping(&checkers[i], i);
connect(&checkers[i], &QPushButton::clicked, signalMapper, &QSignalMapper::map);
}
}
Grid = new QGridLayout;
Grid->setGeometry(QRect(0,0,width,width));
for(int j=0; j<size; j++)
{
for(int i=0; i<size; i++)
{
Grid->addWidget(&checkers[i+j*size], j, i, Qt::AlignmentFlag::AlignCenter);
}
}
GridGroup = new QGroupBox();
GridGroup->setLayout(Grid);
ui->BoardGrid->addWidget(GridGroup);
ui->BoardGrid->setGeometry(QRect(0,0,width,width));
ui->BoardGrid->addWidget(GridGroup);
setWindowTitle("Checkers Game");
ui->P1PieceCount->setFontPointSize(40);
ui->P1PieceCount->setAlignment(Qt::AlignCenter);
ui->P2PieceCount->setFontPointSize(40);
ui->P2PieceCount->setAlignment(Qt::AlignCenter);
ui->TurnCount->setFontPointSize(40);
ui->TurnCount->setAlignment(Qt::AlignCenter);
ui->Player2Name->setAlignment(Qt::AlignCenter);
CheckersBoard(size);
SetInitialDisplay(size);
}
return;
}
How I am trying to access the clicks.
GetClicks() and WaitForClick() functions:
/* This function will get the clicks that are required to make the human move.
* Called by GameWindow::HumanMove */
void GameWindow::GetClicks()
{
connect(this, &GameWindow::SquareClicked, this, &GameWindow::WaitForClick);
}
/* This function will get the clicks that are required to make the human move.
* Called by GameWindow::GetClicks via signal SquareClicked */
void GameWindow::WaitForClick(int square)
{
firstclick = !firstclick;
unsigned int test=square;
if (firstclick ==0 && test != StartPos)
{
StartPos = square;
checkers[square].setChecked(1);
}
else if (firstclick == 1 && test == StartPos)
{
checkers[square].setChecked(0);
}
else if (firstclick==1 && test!= StartPos)
{
EndPos = square;
}
}
The StartPos and EndPos clicked are used in a possible move function to validate the move. It is then updated to the GUI.
Any help on how best to implement this signal and slot mechanism would be greatly appreciated.
Have a look at Qt calculator example?
https://doc.qt.io/qt-5/qtwidgets-widgets-calculator-example.html
you can connect multiple buttons to the same slot.
in slot, find out which button sent the signal using QObject::sender().
Once have the button, extract the position using MyButton::Pos().
(MyButton is the widget used for each of the board button)
i create multiple QPushButtons in the following way:
QList<QByteArray> pBList;
pBList= rec_data.split(',');
for (int i = 1; i < pBList.size() -1; i++){
QPushButton *newpB = new QPushButton(ui->verticalLayoutWidget);
newpB->setText(pBList[i]);
ui->verticalLayoutWidget->layout()->addWidget(newpB);
}
This works fine and the QPushButtons are shown on the GUI.
But how do i connect them to a clicked()-Signal and to a Slot?
I tried it this way, but this dosen't work...
QObject::connect(ui->verticalLayoutWidget->layout()->itemAt(1)->widget(), SIGNAL(clicked()),this, SLOT(_on_send_name()));
Thanks for the help
QList<QByteArray> pBList;
pBList= rec_data.split(',');
for (int i = 1; i < pBList.size() -1; i++){
QPushButton *newpB = new QPushButton(ui->verticalLayoutWidget);
newpB->setText(pBList[i]);
ui->verticalLayoutWidget->layout()->addWidget(newpB);
//This will CONNECT all buttons to a single slot
connect (newpB,&QPushButton::clicked,this,&YOUR_CLASS_NAME::_on_send_name);
}
You can use sender() inside _on_send_name to get a pointer to the clicked button. But sender() is not recommended. https://doc.qt.io/qt-5/qobject.html#sender
I would go with the QSignalMapper for your scenario.
I have a vector.
QVector<QPushButton*> buttonVector;
With this function I add dynamically buttons to the UI.
void MainWindow::createButton()
{
for(int x = 0; x < list.length(); x++)
{
QPushButton *button = new QPushButton(this);
button->setText(QString::number(list.at(x)->ID()));
button->setGeometry(x_cor,y_cor,50,50);
//button->setVisible(true);
buttonVector.append(button);
}
}
At the start of my program this function triggers and works perfectly, every button is showing.
But after I recreate every button with this function after I press a button, they are all invisible if I don't add the line:
button->setVisible(true);
Why is that? At the beginning they are all visible without this line.
I have created a QTableWidget in which I've used setCellWidget(QWidget*). I've set QLineEdit in the cell widget. I've also created a delete button and clicking that button sends a signal to the function deleteRow. I've also used a function currentRow() to get the current row, but it returns -1 because of the QLineEdit. The code snippet is below.
void createTable() {
m_table = new QTableWidget(QDialog); //member variable
for (int i = 0; i < 3; i++)
{
QLineEdit *lineEdit = new QLineEdit(m_table);
m_table->setCellWidget(i, 0, lineEdit);
}
QPushButton *deleteBut = new QPushButton(QDiaolg);
connect(deleteBut, SIGNAL(clicked()), QDialog, SLOT(editRow()));
}
editRow() {
int row = m_table->currentRow(); // This gives -1
m_table->remove(row);
}
In above scenario I click in the QLineEdit and then click on the button delete. Please help me out with a solution.
Just tried it here, it seems that currentRow of the table returns -1 when clicking the button right after program start, and when first selecting a cell, then selecting the QLineEdit and then clicking the button, the correct row is returned.
I would do the following as a workaround: Save the row number in the QLineEdit, e.g. by using QObject::setProperty:
QLineEdit *lineEdit = new QLineEdit(m_table);
lineEdit->setProperty("row", i);
m_table->setCellWidget(i, 0, lineEdit);
Then, in the editRow handler, retrieve the property by asking the QTableWidget for its focused child:
int row = m_table->currentRow();
if (row == -1) {
if (QWidget* focused = m_table->focusWidget()) {
row = focused->property("row").toInt();
}
}
The accepted solution, as is, would not work if rows might get deleted while the program runs. Thus the approach would require to update all the properties. Can be done, if this is a rare operation.
I got away with an iteration approach:
for(unsigned int i = 0; i < table->rowCount(); ++i)
{
if(table->cellWidget(i, relevantColumn) == QObject::sender())
{
return i;
}
}
return -1;
Quick, dirty, but worked, and in my case more suitable, as rows got deleted often or changed their positions, only buttons in the widget were connected to the slot and the slot was never called directly. If these conditions are not met, further checks might get necessary (if(QObject::sender()) { /* */ }, ...).
Karsten's answer will work correctly only if QLineEdit's property is recalculated each time a row is deleted, which might be a lot of work. And Aconcagua's answer works only if the method is invoked via signal/slot mechanism. In my solution, I just calculate the position of the QlineEdit which has focus (assuming all table items were set with setCellWidget):
int getCurrentRow() {
for (int i=0; i<myTable->rowCount(); i++)
for (int j=0; j<myTable->columnCount(); j++) {
if (myTable->cellWidget(i,j) == myTable->focusWidget()) {
return i;
}
}
return -1;
}
void MainWindow::addRadioToUI()
{ int button_cunter=4;
while(!database.isEmpty())
{ button_cunter++;
QPushButton *one = new QPushButton("Play: "+name(get_r.getTrackId()));
one->setIcon(QIcon(":/images/play_button.png"));
one->setMaximumWidth(140);
one->setFlat(true);
QGroupBox* get_rGB = new QGroupBox("somethink");
QFormLayout* layout = new QFormLayout;
if(button_cunter%5 == 0){
layout->addWidget(one);
}
get_rGB->setLayout(layout);
scrollAreaWidgetContents->layout()->addWidget(get_rGB);
}
}
I have a few QPushButtons which are added automaticlly.
Is there a way to add "id attribute or sth else" to button and next know which button was clicked? I have different action for each button.
QApplication offers sender() which contains which object sent the signal. So you can do:
//slot, this could also be done in a switch
if(button[X] == QApplication::sender()){
doX();
}else if(button[Y] == QApplication::sender()){
doY();
}
http://doc.qt.io/qt-4.8/qobject.html#sender
QSignalMapper is pretty good for this type of thing.
You would define your slot like this for instance:
public slots:
void clicked(int buttonId); // or maybe trackId
Then add a QSignalMapper* member to your class and connect it to that slot:
signalMapper = new QSignalMapper(this);
connect(signalMapper, SIGNAL(mapped(int)),
this, SLOT(clicked(int)));
In the addRadioToUI, after creating your push button, do:
signalMapper.setMapping(one, button_cunter);
// or trackId if that's more practical
If all you need is a pointer to the object that triggered the signal though, you can use the static QOjbect::sender function in your slot to get a handle to that.
Use QButtonGroup. It takes id as a parameter when a button is added and provides the id to a slot when a button in the group is pressed.