Difference between revisions of "Development/Tutorials/Qt4 Ruby Tutorial/Chapter 04"

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</code>
 
</code>
  
Here we create a new class. Because this class inherits from Qt::Widget, the new class is a widget and may be a top-level window or a child widget (like the Qt::PushButton in the previous chapter).  
+
Here we create a new class. Because this class inherits from [http://doc.qt.nokia.com/latest/qwidget.html Qt::Widget], the new class is a widget and may be a top-level window or a child widget (like the [http://doc.qt.nokia.com/latest/qpushbutton.html Qt::PushButton] in the previous chapter).  
  
 
<code ruby>
 
<code ruby>
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</code>
 
</code>
  
This class has only one member, a constructor (in addition to the members it inherits from Qt::Widget). The constructor is a standard Qt widget constructor; you should always include a similar constructor when you create widgets.  
+
This class has only one member, a constructor (in addition to the members it inherits from [http://doc.qt.nokia.com/latest/qwidget.html Qt::Widget]). The constructor is a standard Qt widget constructor; you should always include a similar constructor when you create widgets.  
  
The argument is its parent widget. To create a top-level window you specify nil as the parent. As you can see, this widget defaults to be a top-level window.  
+
The argument is its parent widget. To create a top-level window you specify '''<tt>nil</tt>''' as the parent. As you can see, this widget defaults to be a top-level window.  
  
Like most widgets, it just passes on the parent parameter to the Qt::Widget constructor. (If you're new to Ruby, calling super without any parameters will automatically pass on any parameters a method received to the superclass's method of the same name. Update: Apparently, it's also important to leave off the parentheses — calling super() will call the superclass's method of the same name with an empty parameter list.)  
+
Like most widgets, it just passes on the '''<tt>parent</tt>''' parameter to the [http://doc.qt.nokia.com/latest/qwidget.html Qt::Widget] constructor. (If you're new to Ruby, calling '''<tt>super</tt>''' without any parameters will automatically pass on any parameters a method received to the superclass's method of the same name. Update: Apparently, it's also important to leave off the parentheses — calling '''<tt>super()</tt>''' will call the superclass's method of the same name with an empty parameter list.)  
  
 
<code ruby>
 
<code ruby>
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</code>
 
</code>
  
Here we create and set up a child widget of this widget (the new widget's parent is self, i.e. the MyWidget instance).  
+
Here we create and set up a child widget of this widget (the new widget's parent is '''<tt>self</tt>''', i.e. the '''<tt>MyWidget</tt>''' instance).  
  
The QObject::tr() function call around the string literal 'Quit' marks the string for translation, making it possible to change it at run-time based on the contents of a translation file. It is a good habit to use QObject::tr() around all user-visible strings, in case you decide later to translate your application to other languages.  
+
The [http://doc.qt.nokia.com/latest/qobject.html#tr QObject::tr()] function call around the string literal 'Quit' marks the string for translation, making it possible to change it at run-time based on the contents of a translation file. It is a good habit to use [http://doc.qt.nokia.com/latest/qobject.html#tr QObject::tr()] around all user-visible strings, in case you decide later to translate your application to other languages.  
  
The Qt::Widget::setGeometry() call sets both the widget's screen position and the size. It is equivalent to calling Qt::Widget::move() followed by Qt::Widget::resize().  
+
The [http://doc.qt.nokia.com/latest/qwidget.html#geometry-prop Qt::Widget::setGeometry()] call sets both the widget's screen position and the size. It is equivalent to calling [http://doc.qt.nokia.com/latest/qwidget.html#pos-prop Qt::Widget::move()] followed by [http://doc.qt.nokia.com/latest/qwidget.html#size-prop Qt::Widget::resize()].  
  
 
<code ruby>
 
<code ruby>
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</code>
 
</code>
  
The $qApp pointer is a global variable created when you require 'Qt'. It points to the application's unique Qt::Application instance.  
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The '''<tt>$qApp</tt>''' pointer is a global variable created when you '''<tt>require 'Qt'</tt>'''. It points to the application's unique [http://doc.qt.nokia.com/latest/qapplication.html Qt::Application] instance.  
  
 
<code ruby>
 
<code ruby>
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=== Exercises ===
 
=== Exercises ===
  
Try to create another MyWidget object. What happens?  
+
Try to create another '''<tt>MyWidget</tt>''' object. What happens?  
  
Try to add more buttons or put in widgets other than Qt::PushButton.
+
Try to add more buttons or put in widgets other than [http://doc.qt.nokia.com/latest/qpushbutton.html Qt::PushButton].

Revision as of 02:38, 30 December 2009


Contents

Development/Tutorials/Qt4 Ruby Tutorial/Chapter 4


Let There Be Widgets
Tutorial Series   Qt4 Ruby Tutorial
Previous   Tutorial 3 - Family Values
What's Next   Tutorial 5 - Building Blocks
Further Reading   n/a

Let There Be Widgets

Qt4 Ruby Tutorial Screenshot 4.png

Files:

Overview

This example shows how to create your own widget, and describes how to control the minimum and maximum sizes of a widget.

require 'Qt4'

class MyWidget < Qt::Widget

 def initialize(parent = nil)
   super
   setFixedSize(200, 120)
   quit = Qt::PushButton.new(tr('Quit'), self)
   quit.setGeometry(62, 40, 75, 30)
   quit.setFont(Qt::Font.new('Times', 18, Qt::Font::Bold))
   connect(quit, SIGNAL('clicked()'), $qApp, SLOT('quit()'))
 end

end

app = Qt::Application.new(ARGV)

widget = MyWidget.new() widget.show()

app.exec()

Line by Line Walkthrough

class MyWidget < Qt::Widget

Here we create a new class. Because this class inherits from Qt::Widget, the new class is a widget and may be a top-level window or a child widget (like the Qt::PushButton in the previous chapter).

 def initialize(parent = nil)
   super

This class has only one member, a constructor (in addition to the members it inherits from Qt::Widget). The constructor is a standard Qt widget constructor; you should always include a similar constructor when you create widgets.

The argument is its parent widget. To create a top-level window you specify nil as the parent. As you can see, this widget defaults to be a top-level window.

Like most widgets, it just passes on the parent parameter to the Qt::Widget constructor. (If you're new to Ruby, calling super without any parameters will automatically pass on any parameters a method received to the superclass's method of the same name. Update: Apparently, it's also important to leave off the parentheses — calling super() will call the superclass's method of the same name with an empty parameter list.)

   setFixedSize(200, 120)

Because this widget doesn't know how to handle resizing, we fix its size. In the next chapter, we will show how a widget can respond to resize event from the user.

   quit = Qt::PushButton.new(tr('Quit'), self)
   quit.setGeometry(62, 40, 75, 30)
   quit.setFont(Qt::Font.new('Times', 18, Qt::Font::Bold))

Here we create and set up a child widget of this widget (the new widget's parent is self, i.e. the MyWidget instance).

The QObject::tr() function call around the string literal 'Quit' marks the string for translation, making it possible to change it at run-time based on the contents of a translation file. It is a good habit to use QObject::tr() around all user-visible strings, in case you decide later to translate your application to other languages.

The Qt::Widget::setGeometry() call sets both the widget's screen position and the size. It is equivalent to calling Qt::Widget::move() followed by Qt::Widget::resize().

   connect(quit, SIGNAL('clicked()'), $qApp, SLOT('quit()'))

The $qApp pointer is a global variable created when you require 'Qt'. It points to the application's unique Qt::Application instance.

app = Qt::Application.new(ARGV)

widget = MyWidget.new() widget.show()

app.exec()

Here we instantiate our new child, set it to be the main widget, and execute the application.

Running the Application

This program is very similar in behavior to the previous one. The difference lies in the way we have implemented it. It does behave slightly differently, however. Just try to resize it to see.

Exercises

Try to create another MyWidget object. What happens?

Try to add more buttons or put in widgets other than Qt::PushButton.


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