EnArBgDeElEsFaFiFrHiHuItJaKnKoMsNlPlPtRuSqThTrUkZh
Signals and slots are loosely coupled: a class which emits a signal neither knows nor cares which slots receive the signal. Qt's signals and slots mechanism ensures that if you connect a signal to a slot, the slot will be called with the signal's parameters at the right time. Signals and slots can take any number of arguments of any type.
- Signals and slots are loosely coupled: A class which emits a signal neither knows nor cares which slots receive the signal. Qt's signals and slots mechanism ensures that if you connect a signal to a slot, the slot will be called with the signal's parameters at the right time. Signals and slots can take any number of arguments of any type.
- So I used a namespace alias within my app. The project file uses the preprocessor to control which alias is declared and this allows my app to compile with the right library and to use the right namespace name. This works with everything except connect, signals, and slots. When I compile, I get errors that there is no namespace with the name alias.
- Slots and signals must have same parameters. Otherwise, the connection will not occur. Not only for connection, slot function must have same parameters with signal. For example, this sample doesn’t work: QObject::connect(ui.comboBox, SIGNAL (activated(int)), this, SLOT (onComboboxActivated)); But it works.
- So by declaring and implementing a slot with a name that follows the following convention: void on ('); uic (the User Interface Compiler of Qt) will automatically generate code in the dialog's setupUi function to connect button's signal with dialog's slot.
Using QTableWidget developers can embed tables inside Qt applications. QTableWidget inherits QTableView. Items in a QTableWidget instance are provided by class QTableWidgetItem.
Basic Usage
Set number of rows and columns
m_pTableWidget->setRowCount(10);m_pTableWidget->setColumnCount(3);
Insert labels into the horizontal header
m_TableHeader<<'#'<<'Name'<<'Text';m_pTableWidget->setHorizontalHeaderLabels(m_TableHeader);
Insert data
The simplest way to insert text into a cell:m_pTableWidget->setItem(0, 1, new QTableWidgetItem('Hello'));
Hide vertical header aka the line counter
m_pTableWidget->verticalHeader()->setVisible(false);
Hide grid
m_pTableWidget->setShowGrid(false);
Set background of the selected items
m_pTableWidget->setStyleSheet('QTableView {selection-background-color: red;}');
Disable editing
m_pTableWidget->setEditTriggers(QAbstractItemView::NoEditTriggers);
Selection mode and behavior
The behavior of the table for selecting rows and cells can be customized using methods setSelectionBehavior and setSelectionMode. The following example allows only single selection of a row:
m_pTableWidget->setSelectionBehavior(QAbstractItemView::SelectRows);m_pTableWidget->setSelectionMode(QAbstractItemView::SingleSelection);
Handling signals
QTableWidget provides appropriate signals for each event such as change of selection, click, double click, etc. Example of handling double click of a cell:
connect( m_pTableWidget, SIGNAL( cellDoubleClicked (int, int) ), this, SLOT( cellSelected( int, int ) ) );
Example
The following code snippet uses QTableWidget and all described cases above. It has been tested on Symbian^3 device.
- mainwindow.h
#include <QTableWidget>
private slots:
void cellSelected(int nRow, int nCol);
private:
QTableWidget* m_pTableWidget;
QStringList m_TableHeader;
- mainwindow.cpp
- include 'mainwindow.h'
- include <QApplication>
- include <QDesktopWidget>
- include <QCoreApplication>
- include <QHeaderView>
- include <QMessageBox>
MainWindow::MainWindow(QWidget *parent)
{
connect( m_pTableWidget, SIGNAL( cellDoubleClicked (int, int) ),
}
MainWindow::~MainWindow(){}
void MainWindow::cellSelected(int nRow, int nCol){
}
Qt5 alpha has been released. One of the features which I have been working on is a new syntax for signals and slot.This blog entry will present it.
Here is how you would connect a signal to a slot:
What really happens behind the scenes is that the SIGNAL and SLOT macros will convert their argument to a string. Then QObject::connect() will compare those strings with the introspection data collected by the moc tool.
What's the problem with this syntax?
While working fine in general, we can identify some issues:
- No compile time check: All the checks are done at run-time by parsing the strings. That means if you do a typo in the name of the signal or the slot, it will compile but the connection will not be made, and you will only notice a warning in the standard output.
- Since it operates on the strings, the type names of the slot must match exactly the ones of the signal. And they also need to be the same in the header and in the connect statement. This means it won't work nicely if you want to use
typedefor namespaces
In the upcoming Qt5, an alternative syntax exist. The former syntax will still work. But you can now also use this new way of connecting your signals to your slots:
Which one is the more beautiful is a matter of taste. One can quickly get used to the new syntax.
So apart from the aesthetic point of view, let us go over some of the things that it brings us:
Compile-time checking
You will get a compiler error if you misspelled the signal or slot name, or if the arguments of your slot do not match those from the signal.
This might save you some time while you are doing some re-factoring and change the name or arguments of signals or slots.
An effort has been made, using static_assert to get nice compile errors if the arguments do not match or of you miss a Q_OBJECT
Arguments automatic type conversion
Not only you can now use typedef or namespaces properly, but you can also connect signalsto slots that take arguments of different types if an implicit conversion is possible
In the following example, we connect a signal that has a QString as a parameter to a slot that takes a QVariant. It works because QVariant has an implicit constructor that takes a QString
Connecting to any function
As you might have seen in the previous example, the slot was just declared as publicand not as slot. Qt will indeed call directly the function pointer of the slot, andwill not need moc introspection anymore. (It still needs it for the signal)
But what we can also do is connecting to any function or functor:
Qt Connect Slot By Name
This can become very powerful when you associate that with boost or tr1::bind.
C++11 lambda expressions
Everything documented here works with the plain old C++98. But if you use compiler that supportsC++11, I really recommend you to use some of the language's new features.Lambda expressions are supportedby at least MSVC 2010, GCC 4.5, clang 3.1. For the last two, you need to pass -std=c++0x asa flag.
You can then write code like:
This allows you to write asynchronous code very easily.
Qt Connect Slots By Name Search
EnArBgDeElEsFaFiFrHiHuItJaKnKoMsNlPlPtRuSqThTrUkZh
Signals and slots are loosely coupled: a class which emits a signal neither knows nor cares which slots receive the signal. Qt's signals and slots mechanism ensures that if you connect a signal to a slot, the slot will be called with the signal's parameters at the right time. Signals and slots can take any number of arguments of any type.
- Signals and slots are loosely coupled: A class which emits a signal neither knows nor cares which slots receive the signal. Qt's signals and slots mechanism ensures that if you connect a signal to a slot, the slot will be called with the signal's parameters at the right time. Signals and slots can take any number of arguments of any type.
- So I used a namespace alias within my app. The project file uses the preprocessor to control which alias is declared and this allows my app to compile with the right library and to use the right namespace name. This works with everything except connect, signals, and slots. When I compile, I get errors that there is no namespace with the name alias.
- Slots and signals must have same parameters. Otherwise, the connection will not occur. Not only for connection, slot function must have same parameters with signal. For example, this sample doesn’t work: QObject::connect(ui.comboBox, SIGNAL (activated(int)), this, SLOT (onComboboxActivated)); But it works.
- So by declaring and implementing a slot with a name that follows the following convention: void on ('); uic (the User Interface Compiler of Qt) will automatically generate code in the dialog's setupUi function to connect button's signal with dialog's slot.
Using QTableWidget developers can embed tables inside Qt applications. QTableWidget inherits QTableView. Items in a QTableWidget instance are provided by class QTableWidgetItem.
Basic Usage
Set number of rows and columns
m_pTableWidget->setRowCount(10);m_pTableWidget->setColumnCount(3);
Insert labels into the horizontal header
m_TableHeader<<'#'<<'Name'<<'Text';m_pTableWidget->setHorizontalHeaderLabels(m_TableHeader);
Insert data
The simplest way to insert text into a cell:m_pTableWidget->setItem(0, 1, new QTableWidgetItem('Hello'));
Hide vertical header aka the line counter
m_pTableWidget->verticalHeader()->setVisible(false);
Hide grid
m_pTableWidget->setShowGrid(false);
Set background of the selected items
m_pTableWidget->setStyleSheet('QTableView {selection-background-color: red;}');
Disable editing
m_pTableWidget->setEditTriggers(QAbstractItemView::NoEditTriggers);
Selection mode and behavior
The behavior of the table for selecting rows and cells can be customized using methods setSelectionBehavior and setSelectionMode. The following example allows only single selection of a row:
m_pTableWidget->setSelectionBehavior(QAbstractItemView::SelectRows);m_pTableWidget->setSelectionMode(QAbstractItemView::SingleSelection);
Handling signals
QTableWidget provides appropriate signals for each event such as change of selection, click, double click, etc. Example of handling double click of a cell:
connect( m_pTableWidget, SIGNAL( cellDoubleClicked (int, int) ), this, SLOT( cellSelected( int, int ) ) );
Example
The following code snippet uses QTableWidget and all described cases above. It has been tested on Symbian^3 device.
- mainwindow.h
#include <QTableWidget>
private slots:
void cellSelected(int nRow, int nCol);
private:
QTableWidget* m_pTableWidget;
QStringList m_TableHeader;
- mainwindow.cpp
- include 'mainwindow.h'
- include <QApplication>
- include <QDesktopWidget>
- include <QCoreApplication>
- include <QHeaderView>
- include <QMessageBox>
MainWindow::MainWindow(QWidget *parent)
{
connect( m_pTableWidget, SIGNAL( cellDoubleClicked (int, int) ),
}
MainWindow::~MainWindow(){}
void MainWindow::cellSelected(int nRow, int nCol){
}
Qt5 alpha has been released. One of the features which I have been working on is a new syntax for signals and slot.This blog entry will present it.
Here is how you would connect a signal to a slot:
What really happens behind the scenes is that the SIGNAL and SLOT macros will convert their argument to a string. Then QObject::connect() will compare those strings with the introspection data collected by the moc tool.
What's the problem with this syntax?
While working fine in general, we can identify some issues:
- No compile time check: All the checks are done at run-time by parsing the strings. That means if you do a typo in the name of the signal or the slot, it will compile but the connection will not be made, and you will only notice a warning in the standard output.
- Since it operates on the strings, the type names of the slot must match exactly the ones of the signal. And they also need to be the same in the header and in the connect statement. This means it won't work nicely if you want to use
typedefor namespaces
In the upcoming Qt5, an alternative syntax exist. The former syntax will still work. But you can now also use this new way of connecting your signals to your slots:
Which one is the more beautiful is a matter of taste. One can quickly get used to the new syntax.
So apart from the aesthetic point of view, let us go over some of the things that it brings us:
Compile-time checking
You will get a compiler error if you misspelled the signal or slot name, or if the arguments of your slot do not match those from the signal.
This might save you some time while you are doing some re-factoring and change the name or arguments of signals or slots.
An effort has been made, using static_assert to get nice compile errors if the arguments do not match or of you miss a Q_OBJECT
Arguments automatic type conversion
Not only you can now use typedef or namespaces properly, but you can also connect signalsto slots that take arguments of different types if an implicit conversion is possible
In the following example, we connect a signal that has a QString as a parameter to a slot that takes a QVariant. It works because QVariant has an implicit constructor that takes a QString
Connecting to any function
As you might have seen in the previous example, the slot was just declared as publicand not as slot. Qt will indeed call directly the function pointer of the slot, andwill not need moc introspection anymore. (It still needs it for the signal)
But what we can also do is connecting to any function or functor:
Qt Connect Slot By Name
This can become very powerful when you associate that with boost or tr1::bind.
C++11 lambda expressions
Everything documented here works with the plain old C++98. But if you use compiler that supportsC++11, I really recommend you to use some of the language's new features.Lambda expressions are supportedby at least MSVC 2010, GCC 4.5, clang 3.1. For the last two, you need to pass -std=c++0x asa flag.
You can then write code like:
This allows you to write asynchronous code very easily.
Qt Connect Slots By Name Search
Update: Also have a look what other C++11 features Qt5 offers.
Qt Connect Slots By Name No Matching Signal
It is time to try it out. Check out the alpha and start playing. Don't hesistate to report bugs.
