I have this class in button.h:
class Buttons : public QObject
{
Q_OBJECT
public:
Buttons();
QVector<QPushButton*> buttons;
public slots:
void getBtnInfo();
};
and in mainwindow.cpp, I connect like this:
Buttons mButtons;
for(int i = 0; i < mButtons.buttons.size(); i++) {
mButtons.buttons[i] = new QPushButton(mCentralWidget);
...
connect(mButtons.buttons[i], SIGNAL(clicked(bool)), &mButtons, SLOT(getBtnInfo()));
}
It runs without any errors; but the getBtnInfo() slot seems like not do anything. Because I tried simply just debug in this slot, not working.
But if I declare getBtnInfo() slot in mainwindow.h and connect like this:
connect(mButtons.buttons[i], SIGNAL(clicked(bool)), this, SLOT(getBtnInfo()));
then it works.
I wonder why? And how do I solve the problem above?
Thanks.
If a variable is created in a function it only exists in that function, then it will not be accessible, and that is what I think is happening, I recommend you to make mButtons a member of the class.
*.h
private:
Buttons mButtons;
Related
I want to implement signal and slot between two classes mainwindow and reader.
Inside the reader class I declare the signal SetProgress:
reader.h
class reader :public QObject
{
Q_OBJECT
signals:
void SetProgress(QString sOperation, int nPercentage);
}
reader.cpp
void reader::UpdateProgress(double amount)
{
int nPrecentage = (100 * amount / (max- min));
emit SetProgress(m_sCurrentOperation, nPrecentage);
}
mainwindow.h
public:
reader *MyReader
private slots:
void SlotDisplayProgress(QString sActivity_i, int ProgressPercentage_i);
mainwindow.cpp
void mainwindow :: SlotDisplayProgress(QString sActivity_i, int nProgressPercentage_i)
{
this->ui->QprogressBar->setValue(nProgressPercentage_i);
}
inside Mainwidow.cpp I will declare signal and slot
MyReader = reader::New();
connect ( MyReader, &reader::SetProgress, this, &mainwindow::SlotDisplayProgress );
I tried debugging and everything works correctly till the emit part. However, the slot is never executed.
Try setting Qt::DirectConnection:
connect ( MyReader, &reader::SetProgress, this, &mainwindow::SlotDisplayProgress, ***Qt::DirectConnection***);
I had a problem like this, where I connected the signal and slot, and it only worked when I defined the type of connection.
I hope this helps.
PS. I don't know if this depends on the version of QT but when I connect signals and slots the syntax I write is the following:
ImageURLLoadListener* downloader = new ImageURLLoadListener(&id, socket);
connect(downloader, SIGNAL(imageLoaded(QString*,QTcpSocket*)), this, SLOT(on_resourceImageDownload(QString*,QTcpSocket*)), Qt::DirectConnection);
I don't know if it's related or not...
Is MyReader pointer? Use &MyReader if not so.
I have problem with actually running QActions created with QtCreator. To run e.g. actionSystemSettings, I've added slot to MainWindows so it looks like this:
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private slots:
void on_menuWork_actionSystemSettings();
private:
Ui::MainWindow *ui;
};
And this:
void MainWindow::on_menuWork_actionSystemSettings() {
qDebug() << "Yay!";
}
It prompts:
QMetaObject::connectSlotsByName: No matching signal for
on_menuWork_actionSystemSettings()
I guess it's some dumb mistake and I just forgot about something but reading documentation gives me nothing. I have no "go to slot" menu entry which should auto-create some template... at least Visual Studio for C# did that.
When you're defining slots the correct way is:
on_<widget_name>_<signal>
for instance if you have to name your slot
private slots:
on_actionSystemSettings_triggered();
See QtAutoConnect
According to the documentation for QMetaObject::connectSlotsByName():
Searches recursively for all child objects of the given object, and
connects matching signals from them to slots of object that follow the
following form:
void on_object-name_signal-name(signal-parameters);
So, I think your slot should have the following signature:
void MainWindow::on_actionSystemSettings_triggered()
{
//
}
I have a small problem. I want run function in MainWindow from AnotherWindow. I can't set connect() for it.
Main class: MainWindow
Other form: AnotherWindow
Function in main class: setVariable(QString)
Function in other form: btnClicked()
I have now connected button signal clicked():
// In AnotherWindow.cpp
connect(ui->btnOK, SIGNAL(clicked()), this, SLOT(btnOkClicked()));
// Function in same file
void interfaceWindow::btnOkClicked() {
/* Some actions - emit signal? */
this->close();
}
btnOkClicked() are declared as private slot.
// In MainWindow.cpp
void MainWindow::setVariable(QString _var) {
this->var = _var;
}
setVariable(QString) are declared as public slot.
How I can send variable from AnotherForm (from btnOkClicked() function) to MainWindow (setVariable(QString) function) ? How and where I must send signal and make connection?
I readed about signals and slots, but my code don't work - I don't paste it here because it's terrible :)
Any help for Qt newbie?
You need to have an reference of AnotherWindow in MainWindow OR vice versa. Then you need the following things:
// AnotherWindow.h
signals:
void buttonOkClickedSignal(QString var);
// AnotherWindow.cpp
void interfaceWindow::btnOkClicked() {
emit buttonOkClickedSignal("The button got clicked!");
this->close();
}
Next step varies based on whether MainWindow has reference to AnotherWindow or vice versa. You can either:
// AnotherWindow.cpp
connect(this, SIGNAL(buttonOkClickedSignal(QString), &mainWindow, SLOT(setVariable(QString)));
or:
// MainWindow.cpp
connect(&anotherWindow, SIGNAL(buttonOkClickedSignal(QString), this, (SLOT(setVariable(QString)));
If you are invoking the slot through signal it shouldn't matter whether it's private or public (see Qt Documentation).
Hope this helps.
I'm not entirely sure I understand your question, but let me try.
You want to be able to fire a slot in another class. There are a few ways you can do that.
Declare one as a friend class to the other. Then they can see the protected and private variables/memebers
It is possible to make slots static so you can call them without a class object.
For example,
class MainWindow {
private slot:
void setVariable(QString);
}
class AnotherWindow {
friend class MainWindow;
MainWindow *window;
public:
AnotherWindow() {
connect(this, SIGNAL(fire(QString)), window, SLOT(setVariable(QString)));
}
signals:
void fire(QString);
public slots:
void onButtonClicked() {
emit fire(QString);
}
}
The previous is pseudocode so don't expect it to compile. I think this is what you want. Basically since your slot is private on MainWindow you need to make it a friend. To connect, it needs to be a member. Then when the onButtonClicked slot is evoked, then it fire()s the setVarialbe() slot.
Here is a simple code for your another window:
class MyWidget : public QWidget
{
Q_OBJECT
public:
MyWidget(QWidget * parent = 0)
{
okBtn = new QPushButton ("I am Ok!");
MyData = "";
connect(okBtn ,SIGNAL(clicked()),this,SLOT(OnOk()));
}
~MyWidget();
private:
QString MyData;
QPushButton * okBtn;
//something that modify string MyData
signals:
void MyDataSignal(QString);
//Internal slot that emits signal with proper data
private slots:
void OnOk()
{
if(MyData!="")
{
emit MyDataSignal(MyData);
}
}
};
Now in MainWindow create an object of MyWidget (suppose myWid)and connect it to slot
connect(myWid, SIGNAL(MyDataSignal(QString)),this,SLOT(OnMyWidOkClicked(QString)));
the signal will pass string to slot.
While making signals and slots keep in mind following points:
To connect a signal to a slot (or to another signal), they must have the same parameter
Parameters should be in the same order in both signal and slot.
if a signal has more parameters than the slot it is connected to, the additional parameters are simply ignored but opposite is not possible.
If you will connect a signal that have unmatched parameters to slot then no compile time error will occur but at run time command window will show a warning that signal/slot/connection does not exist.
I'm trying to change text of a class Label from another class. I have class MainWindow, which contains Label.
I also have a Bot class from which I wanna change the value of label.
I'm trying to create signal and slots but I have no idea where to start.
I created signal and slots like so:
//in mainwindow.h
signals:
void changeTextSignal();
private slots:
void changeText();
//in mainwindow.cpp
void MainWindow::changeText(){
this->label->setText("FooBar");
}
But I have no idea how to connect a signal to be able to change Label's text from another class.
Read up on Qt signal-slot mechanism. If I understand you correctly, you are trying to signal from Bot to MainWindow that the Label text needs to change. Here's how you do it...
//bot.h
class Bot
{
Q_OBJECT;
//other stuff here
signals:
void textChanged(QString);
public:
void someFunctionThatChangesText(const QString& newtext)
{
emit textChanged(newtext);
}
}
//mainwindow.cpp
MainWindow::MainWindow
{
//do other stuff
this->label = new QLabel("Original Text");
mybot = new Bot; //mybot is a Bot* member of MainWindow in this example
connect(mybot, SIGNAL(textChanged(QString)), this->label, SLOT(setText(QString)));
}
void MainWindow::hello()
{
mybot->someFunctionThatChangesText("Hello World!");
}
Here's a simple code that creates a button and assigns a onclick handler:
auto btn = new QPushButton("CLICK ME");
connect(btn, SIGNAL(clicked()), this, SLOT(btn_Click()));
private slots:
void btn_Click() {
alert("clicked!");
}
It works as it should if called in the main window class. However when I try to do this in a child window, clicking the button does nothing. The child window is shown like this:
auto settingsWindow = new SettingsWindow();
settingsWindow->show();
I guess it's somehow connected with the receiver object which is now a different window. But how can I make it work?
In order to be able to declare signals/slots in your own class you should include Q_OBJECT directive in your class:
class SettingsWindow {
Q_OBJECT
...
};
You should add a MACRO in class SettingsWindow to enable singal receiving.
Add "Q_OBJECT" like the following.
class MainWidget : public QWidget
{
Q_OBJECT
public:
MainWidget();
....