Development/Tutorials/Kross/Connecting Signals and slots in Kross: Difference between revisions

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{{Under Construction}}
{{Review|Port to KF5}}


This tutorial shows how to use a system of signals and slots to provide a scripting interface for a KDE application. It builds upon the [[Development/Tutorials/Kross/Hello World|Kross Hello World]] tutorial and again follows a 'Hello World' type format.
This tutorial shows how to use a system of signals and slots to provide a scripting interface for a KDE application. It builds upon the [[Development/Tutorials/Kross/Hello World|Kross Hello World]] tutorial and again follows a 'Hello World' type format.
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First edit the mainwindow.h to handle the changes to mainwindow.cpp. Note that the change is the addition of a private <tt>Kross::Action</tt> .
First edit the mainwindow.h to handle the changes to mainwindow.cpp. Note that the change is the addition of a private <tt>Kross::Action</tt> .


<code cpp>
<syntaxhighlight lang="cpp">
#ifndef MAINWINDOW_H
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#define MAINWINDOW_H
Line 46: Line 46:


#endif
#endif
</code>
</syntaxhighlight>


=== mainwindow.cpp ===
=== mainwindow.cpp ===
Using the same CmakeLists.txt and main.cpp from the previous [[Development/Tutorials/Kross/Hello_World|Hello World]] tutorial, edit the mainwindow.cpp as follows:
Using the same CmakeLists.txt and main.cpp from the previous [[Development/Tutorials/Kross/Hello_World|Hello World]] tutorial, edit the mainwindow.cpp as follows:


<code cpp>
<syntaxhighlight lang="cpp">
#include "mainwindow.h"
#include "mainwindow.h"


Line 112: Line 112:
   action->trigger();
   action->trigger();
}
}
</code>
</syntaxhighlight>


The changes are addition of a text entry field and the reorganisation of logic handling the Kross::Action. Note also that there is no code in mainwindow.cpp to set the label, as there was in the previous tutorial. Instead, Objects are simply made available to the scripting interface through the <tt>action->addObject</tt> calls, without any knowledge of what the script will use them for. This removes the need to know at the time of writing the application what function the scripts will perform, and is therefore suited to a plugin interface.
The changes are addition of a text entry field and the reorganisation of logic handling the Kross::Action. Note also that there is no code in mainwindow.cpp to set the label, as there was in the previous tutorial. Instead, Objects are simply made available to the scripting interface through the <tt>action->addObject</tt> calls, without any knowledge of what the script will use them for. This removes the need to know at the time of writing the application what function the scripts will perform, and is therefore suited to a plugin interface.
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This script catches the textChanged SIGNAL of the QLineEdit, and connects it to a simple python function to reverse the string in the QLineEdit and display it in the QLabel.
This script catches the textChanged SIGNAL of the QLineEdit, and connects it to a simple python function to reverse the string in the QLineEdit and display it in the QLabel.


<code python>
<syntaxhighlight lang="python">
#!/usr/bin/env kross
#!/usr/bin/env kross


Line 131: Line 131:


MyInputString.connect("textChanged(const QString &)", reverseString)
MyInputString.connect("textChanged(const QString &)", reverseString)
</code>
</syntaxhighlight>


=== krossSigsSlots.js ===
=== krossSigsSlots.js ===
This script does the same as the script above but using the JavaScript scripting language.
This script does the same as the script above but using the JavaScript scripting language.


<code javascript>
<syntaxhighlight lang="javascript">
function reverseString(s){
function reverseString(s){
     MyLabel.text = s.split("").reverse().join("");
     MyLabel.text = s.split("").reverse().join("");
Line 143: Line 143:
connect(MyInputString, "textChanged(const QString &)", this, "reverseString(const QString &)");
connect(MyInputString, "textChanged(const QString &)", this, "reverseString(const QString &)");


</code>
</syntaxhighlight>


{{TODO|Write similar for other interpreters}}
{{TODO|Write similar for other interpreters}}
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It is possible to connect signals from your Object to slots in your script file automatically. Edit the mainwindow.cpp file to add another argument to the addObject function:
It is possible to connect signals from your Object to slots in your script file automatically. Edit the mainwindow.cpp file to add another argument to the addObject function:


<code cpp>
<syntaxhighlight lang="cpp">
action->addObject(txtInputString, "MyInputString",
action->addObject(txtInputString, "MyInputString",
                   Kross::ChildrenInterface::AutoConnectSignals);
                   Kross::ChildrenInterface::AutoConnectSignals);
Line 157: Line 157:
action->addObject(cmbInterpreters, "MyInterpreter");
action->addObject(cmbInterpreters, "MyInterpreter");
action->addObject(lblMessage, "MyLabel");
action->addObject(lblMessage, "MyLabel");
</code>
</syntaxhighlight>
The <tt>Kross::ChildrenInterface::AutoConnectSignals</tt> argument causes signals of the object to be automatically connected with scripting functions of the same name. Therefore, the scripts can again be simplified:
The <tt>Kross::ChildrenInterface::AutoConnectSignals</tt> argument causes signals of the object to be automatically connected with scripting functions of the same name. Therefore, the scripts can again be simplified:


=== Simplified scripts ===
=== Simplified scripts ===
The following python code provides a function that reverses the string:
The following python code provides a function that reverses the string:
<code python>
<syntaxhighlight lang="python">
import MyLabel
import MyLabel


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   s = s[::-1]
   s = s[::-1]
   MyLabel.text = s
   MyLabel.text = s
</code>
</syntaxhighlight>


Now follows a javascript function that converts the string to [http://en.wikipedia.org/wiki/Pig_Latin|pig latin]:
Now follows a javascript function that converts the string to [http://en.wikipedia.org/wiki/Pig_Latin pig latin]:


<code javascript>
<syntaxhighlight lang="javascript">
function textChanged(text)
function textChanged(text)
{
{
Line 179: Line 179:
   MyLabel.text = pigLatin;
   MyLabel.text = pigLatin;
}
}
</code>
</syntaxhighlight>


{{TODO|Write similar for other interpreters}}
{{TODO|Write similar for other interpreters}}
Line 189: Line 189:
So far this tutorial has described connecting signals in c++ objects with slots in scripts. The objects published to kross scripts also make their signals available to the scripts. The signals can then be emitted by calling them. This is equivalent to calling:
So far this tutorial has described connecting signals in c++ objects with slots in scripts. The objects published to kross scripts also make their signals available to the scripts. The signals can then be emitted by calling them. This is equivalent to calling:


<code cpp>
<syntaxhighlight lang="cpp">
   emit signalName();
   emit signalName();
</code>
</syntaxhighlight>
in c++ code. To illustrate this, change the python script to emit the setEnabled(bool) signal of the QCombobox:
in c++ code. To illustrate this, change the python script to emit the setEnabled(bool) signal of the QCombobox:


<code python>
<syntaxhighlight lang="python">
#!/usr/bin/env kross
#!/usr/bin/env kross


Line 207: Line 207:
   s = MyInputString.text[::-1]
   s = MyInputString.text[::-1]
   MyLabel.text = s
   MyLabel.text = s
</code>
</syntaxhighlight>


If 'off' is written in the text field, the setEnabled signal is emitted and the combobox is greyed out. It is not re-enabled again until 'on' is written in the text field.
If 'off' is written in the text field, the setEnabled signal is emitted and the combobox is greyed out. It is not re-enabled again until 'on' is written in the text field.


This is a simple demonstration of signal-slot relationships using kross. More complex interfaces may be written to complete a plugin architecture.
This is a simple demonstration of signal-slot relationships using kross. More complex interfaces may be written to complete a plugin architecture.

Latest revision as of 08:16, 31 May 2019

Hello world in kross
Tutorial Series   Kross tutorials
Previous   Kross Hello World
What's Next   Scripts as plugins
Further Reading   n/a
Warning
This page needs a review and probably holds information that needs to be fixed.

Parts to be reviewed:

Port to KF5

This tutorial shows how to use a system of signals and slots to provide a scripting interface for a KDE application. It builds upon the Kross Hello World tutorial and again follows a 'Hello World' type format.

Update source files

This tutorial is based on the Hello World tutorial and extends the codebase we wrote there with new functionality.

mainwindow.h

First edit the mainwindow.h to handle the changes to mainwindow.cpp. Note that the change is the addition of a private Kross::Action .

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QComboBox>
#include <QLabel>
#include <QLineEdit>

#include <kross/core/action.h>
 
// The main window to display our combobox and the label.
class MainWindow : public QWidget
{
    Q_OBJECT
  public:
    // The constructor.
    MainWindow(QWidget *parent=0);
  private Q_SLOTS:
    // This slot is called when the item in the combobox is changed.
    void interpreterActivated(const QString &);
  private:
    QLineEdit* txtInputString;
    QLabel* lblMessage;
    QComboBox* cmbInterpreters;
    // We now have the action as class-member.
    Kross::Action* action;
};

#endif

mainwindow.cpp

Using the same CmakeLists.txt and main.cpp from the previous Hello World tutorial, edit the mainwindow.cpp as follows:

#include "mainwindow.h"

#include <QVBoxLayout>
#include <QDebug>

#include <kross/core/manager.h>
#include <kross/core/action.h>

// the constructor.
MainWindow::MainWindow(QWidget *parent) : QWidget(parent)
{
  txtInputString = new QLineEdit();
  lblMessage = new QLabel("Hello");
  cmbInterpreters = new QComboBox ();
  cmbInterpreters->addItem("Choose Interpreter", "");

  foreach(QString s, Kross::Manager::self().interpreters())
    cmbInterpreters->addItem(s);

  connect(cmbInterpreters, SIGNAL(activated(const QString &)),
      SLOT(interpreterActivated(const QString &)));

  QVBoxLayout *vLayout = new QVBoxLayout;
  vLayout->addWidget(cmbInterpreters);
  vLayout->addWidget(txtInputString);
  vLayout->addWidget(lblMessage);
  setLayout(vLayout);

  // This time we create the Kross::Action already within the
  // constructor and add the objects that should be accessible
  // from within scripting code.
  action = new Kross::Action(this, "MyScript");

  action->addObject(txtInputString, "MyInputString");
  action->addObject(cmbInterpreters, "MyInterpreter");
  action->addObject(lblMessage, "MyLabel");
}

// this slot is called when the active item of the combobox changes.
void MainWindow::interpreterActivated(const QString &strSelectedInterpreter)
{
  if(strSelectedInterpreter.isEmpty()) {
    lblMessage->setText("-");
    return;
  }

  // this time we are using external script files.
  QString filename;
  if(strSelectedInterpreter == "python")
    filename = "krossSigsSlots.py";
  else if(strSelectedInterpreter == "javascript")
    filename = "krossSigsSlots.js";
  else
    return;

  // set the script file that should be executed.
  action->setFile(filename);
  // finally execute the scripting code.
  action->trigger();
}

The changes are addition of a text entry field and the reorganisation of logic handling the Kross::Action. Note also that there is no code in mainwindow.cpp to set the label, as there was in the previous tutorial. Instead, Objects are simply made available to the scripting interface through the action->addObject calls, without any knowledge of what the script will use them for. This removes the need to know at the time of writing the application what function the scripts will perform, and is therefore suited to a plugin interface.

krossSigsSlots.py

This script catches the textChanged SIGNAL of the QLineEdit, and connects it to a simple python function to reverse the string in the QLineEdit and display it in the QLabel.

#!/usr/bin/env kross

import MyLabel
import MyInterpreter
import MyInputString

def reverseString(s):
  s = s[::-1]
  MyLabel.text = s

MyInputString.connect("textChanged(const QString &)", reverseString)

krossSigsSlots.js

This script does the same as the script above but using the JavaScript scripting language.

function reverseString(s){
    MyLabel.text = s.split("").reverse().join("");
}

connect(MyInputString, "textChanged(const QString &)", this, "reverseString(const QString &)");
noframe
noframe
 
TODO
Write similar for other interpreters

Autoconnecting Signals and Slots

It is possible to connect signals from your Object to slots in your script file automatically. Edit the mainwindow.cpp file to add another argument to the addObject function:

action->addObject(txtInputString, "MyInputString",
                  Kross::ChildrenInterface::AutoConnectSignals);

action->addObject(cmbInterpreters, "MyInterpreter");
action->addObject(lblMessage, "MyLabel");

The Kross::ChildrenInterface::AutoConnectSignals argument causes signals of the object to be automatically connected with scripting functions of the same name. Therefore, the scripts can again be simplified:

Simplified scripts

The following python code provides a function that reverses the string:

import MyLabel

def textChanged(s):
  s = s[::-1]
  MyLabel.text = s

Now follows a javascript function that converts the string to pig latin:

function textChanged(text)
{
  text = text.replace(/\b([aeiou][a-z]*)\b/gi, "$1way"); // Rule 2
  pigLatin = text.replace(/\b([bcdfghjklmnpqrstvwxyz]+)([a-z]*)\b/gi, "$2$1ay"); // Rule 1
  MyLabel.text = pigLatin;
}
noframe
noframe
 
TODO
Write similar for other interpreters

Emitting signals from within scripts

So far this tutorial has described connecting signals in c++ objects with slots in scripts. The objects published to kross scripts also make their signals available to the scripts. The signals can then be emitted by calling them. This is equivalent to calling:

  emit signalName();

in c++ code. To illustrate this, change the python script to emit the setEnabled(bool) signal of the QCombobox:

#!/usr/bin/env kross

import MyLabel
import MyInterpreter

def textChanged(s):
  if s == "off":
    MyInterpreter.setEnabled(False)
  elif s == "on":
    MyInterpreter.setEnabled(True)
  s = MyInputString.text[::-1]
  MyLabel.text = s

If 'off' is written in the text field, the setEnabled signal is emitted and the combobox is greyed out. It is not re-enabled again until 'on' is written in the text field.

This is a simple demonstration of signal-slot relationships using kross. More complex interfaces may be written to complete a plugin architecture.