The Ring programming language version 1.4 book - Part 19 of 30

Ring Documentation, Release 1.4
Table 51.1 – continued from previous page
Class Name Methods to use the default Events
SetSelectionChangedEvent()
SetTextChangedEvent()
SetUndoAvailableEvent()
QListWidget SetCurrentItemChangedEvent()
SetCurrentRowChangedEvent()
SetCurrentTextChangedEvent()
SetItemActivatedEvent()
SetItemChangedEvent()
SetItemClickedEvent()
SetItemDoubleClickedEvent()
SetItemEnteredEvent()
SetItemPressedEvent()
SetItemSelectionChangedEvent()
QTreeView SetCollapseEvent()
SetExpandedEvent()
SetActivatedEvent()
SetClickedEvent()
SetDoubleClickedEvent()
SetEnteredEvent()
SetPressedEvent()
SetViewportEnteredEvent()
QTreeWidget SetCollapsedEvent()
SetExpandedEvent()
SetActivatedEvent()
SetClickedEvent()
SetDoubleClickedEvent()
SetEnteredEvent()
SetPressedEvent()
SetViewportEnteredEvent()
SetCurrentItemChangedEvent()
SetItemCollapsedEvent()
SetItemExpandedEvent()
QComboBox SetActivatedEvent()
SetCurrentIndexChangedEvent()
SetEditTextChangedEvent()
SetHighlightedEvent()
QTabWidget SetCurrentChangedEvent()
SetTabCloseRequestedEvent()
QTableWidget SetCellActivatedEvent()
SetCellChangedEvent()
SetCellClickedEvent()
SetCellDoubleClickedEvent()
Continued on next page
51.55. Classes and their Methods to use the default events 518

SetCellEnteredEvent()
SetCellPressedEvent()
SetCurrentCellChangedEvent()
SetCurrentItemChangedEvent()
QProgressBar SetValueChangedEvent()
QSpinBox SetValueChangedEvent()
QSlider SetActionTriggeredEvent()
SetRangeChangedEvent()
SetSliderMovedEvent()
SetSliderPressedEvent()
SetSliderReleasedEvent()
SetValueChangedEvent()
QDial SetActionTriggeredEvent()
SetRangeChangedEvent()
SetSliderMovedEvent()
SetSliderPressedEvent()
SetSliderReleasedEvent()
SetValueChangedEvent()
QWebView SetLoadFinishedEvent()
SetLoadProgressEvent()
SetLoadStartedEvent()
SetSelectionChangedEvent()
SetTitleChangedEvent()
SetUrlChangedEvent()
QCheckBox SetStateChangedEvent()
SetClickedEvent()
SetPressedEvent()
SetReleasedEvent()
SetToggledEvent()
QRadioButton SetClickedEvent()
SetPressedEvent()
SetReleasedEvent()
SetToggledEvent()
QButtonGroup SetButtonClickedEvent()
SetButtonPressedEvent()
SetButtonReleasedEvent()
QVideoWidget SetBrightnessChangedEvent()
SetContrastChangedEvent()
SetFullScreenChangedEvent()
SetHueChangedEvent()
SetSaturationChangedEvent()
QTimer SetTimeoutEvent()
Continued on next page
51.55. Classes and their Methods to use the default events 519

QTcpServer SetAcceptErrorEvent()
SetNewConnectionEvent()
QIODevice SetAboutToCloseEvent()
SetBytesWrittenEvent()
SetReadChannelFinishedEvent()
SetReadyReadEvent()
QAbstractSocket SetConnectedEvent()
SetDisconnectedEvent()
SetErrorEvent()
SetHostFoundEvent()
SetProxyAuthenticationRequiredEvent()
SetStateChangedEvent()
QTcpSocket SetConnectedEvent()
SetDisconnectedEvent()
SetErrorEvent()
SetHostFoundEvent()
SetProxyAuthenticationRequiredEvent()
SetStateChangedEvent()
SetAboutToCloseEvent()
SetBytesWrittenEvent()
SetReadChannelFinishedEvent()
SetReadyReadEvent()
QColorDialog SetColorSelectedEvent()
SetCurrentColorChangedEvent()
QNetworkAccessManager SetFinishedEvent()
QThread SetStartedEvent()
SetFinishedEvent()
51.56 Methods to use Events with Events Filter
RingQt deﬁne a new class called QAllEvents that help you in using Events Filter
The next table presents the methods that we have
Methods to get parameters Class Name
getKeyCode() –> Number QAllEvents
getx() –> Number
gety() –> Number
getglobalx() –> Number
getglobaly() –> Number
getbutton() –> Number
getbuttons() –> Number
The next table presents the methods that we have to use events.
51.56. Methods to use Events with Events Filter 520

Method Name Class Name
setKeyPressEvent(cEvent) QAllEvents
setMouseButtonPressEvent(cEvent)
setMouseButtonReleaseEvent(cEvent)
setMouseButtonDblClickEvent(cEvent)
setMouseMoveEvent(cEvent)
setCloseEvent(cEvent)
setContextMenuEvent(cEvent)
setDragEnterEvent(cEvent)
setDragLeaveEvent(cEvent)
setDragMoveEvent(cEvent)
setDropEvent(cEvent)
setEnterEvent(cEvent)
setFocusInEvent(cEvent)
setFocusOutEvent(cEvent)
setKeyReleaseEvent(cEvent)
setLeaveEvent(cEvent)
setNonClientAreaMouseButtonDblClickEvent(cEvent)
setNonClientAreaMouseButtonPressEvent(cEvent)
setNonClientAreaMouseButtonReleaseEvent(cEvent)
setNonClientAreaMouseMoveEvent(cEvent)
setMoveEvent(cEvent)
setResizeEvent(cEvent)
setWindowActivateEvent(cEvent)
setWindowBlockedEvent(cEvent)
setWindowDeactivateEvent(cEvent)
setWindowStateChangeEvent(cEvent)
setWindowUnblockedEvent(cEvent)
51.57 The Difference between Qt and RingQt
1. RingQt use simple methods to set the code that will be executed for events.
Syntax:
Set<Event_Name>Event(cEventCode)
2. RingQt change the name of some methods to avoid conﬂict with Ring Keywords.
The next table present these little changes
51.57. The Difference between Qt and RingQt 521

Class Name Qt Method Name RingQt Method Name
QWebView load loadpage
QMediaPlaylist load loadﬁle
QMediaPlaylist next movenext
QPainter end endpaint
QPicture load loadﬁle
QLineEdit end endtext
QDialog done donedialog
QTextDocument end enddoc
QTextBlock next nextblock
QSqlQuery next movenext
QImage load loadimage
QNetworkAccessManager get getvalue
QNetworkAccessManager put putvalue
QThread exit exitfromthread
QRegularExpressionMatchIterator next nextitem
QCamera load loadcamera
51.58 RingQt Classes and their Qt Documentation
Qt Documentation : http://doc.qt.io/qt-5/classes.html
See the “RingQt Classes and Methods Reference” chapter for supported classes and methods.
51.59 New Classes names - Index Start from 1
We added new classes to RingQt - another version of classes where the class names doesn’t start with the “q” letter
Also updated methods so the index start from 1 when we deal with the GUI controls like
• ComboBox
• ListWidget
• TableWidget
• TreeWidget
These classes are inside guilib.ring under the package name : System.GUI
To use it
load "guilib.ring"
import System.GUI
This doesn’t have any effect on our previous code, It’s just another choice for better code that is consistent with Ring
rules.
Also the form designer is updated to provide us the choice between using classes where (index start from 0) or (index
start from 1)
Example (Uses the Form Designer)
1. https://github.com/ring-lang/ring/blob/master/applications/formdesigner/tests/indexstart/indexstartView.ring
2. https://github.com/ring-lang/ring/blob/master/applications/formdesigner/tests/indexstart/indexstartController.ring
51.58. RingQt Classes and their Qt Documentation 522

CHAPTER
FIFTYTWO
BUILDING RINGQT APPLICATIONS FOR MOBILE
In this chapter we will learn about Building RingQt Applications for Mobile.
52.1 Download Requirements
Check the next link : http://doc.qt.io/qt-5/androidgs.html
Download
• The Android SDK Tools
https://developer.android.com/studio/index.html
• The Android NDK
https://developer.android.com/ndk/index.html
• Apache Ant v1.8 or later
http://ant.apache.org/bindownload.cgi
• Java SE Development Kit (JDK) v6 or later
http://www.oracle.com/technetwork/java/javase/downloads/jdk7-downloads-1880260.html
52.2 Update the Android SDK
Update the Android SDK to get the API and tools packages required for development
52.3 Install Qt for Android
• You can install Qt for Android from the next link
https://download.qt.io/archive/qt/5.5/5.5.1/
• Run Qt Creator, Select Tools > Options > Android to add the Android NDK and SDK paths.
http://doc.qt.io/qtcreator/creator-developing-android.html
• Using Qt Creator Open the project
Folder : ring/android/ringqt/project
Project ﬁle : project.pro
523

• You will find the code in resourcestest.ring
You can modify the code then build and run for Desktop or Mobile.
52.4 Comments about developing for Android using RingQt
1. The main project file is main.cpp
This file load Ring Compiler/Virtual Machine and RingQt
Then copy files during the runtime from the resources to temp. folder
Then run the test.ring
Through main.cpp you can extract more files from the resources to temp. folder once you add them
(create projects with many files).
2. The next functions are missing from this Ring edition
• Database (ODBC, SQLite & MySQL)
• Security and Internet functions (LibCurl & OpenSSL)
• RingAllegro (Allegro Library)
• RingLibSDL (LibSDL Library)
Just use Qt Classes through RingQt.
For database access use the QSqlDatabase Class
Note: All of the missing libraries ((LibCurl, OpenSSL & Allegro) can be compiled for Android, but they are not
included in this Qt project.
3. use if isandroid() when you want to modify the code just for android
52.4. Comments about developing for Android using RingQt 524

Example:
if isandroid()
// Android code
else
// other platforms
ok
(4) Sometimes you will ﬁnd that the button text/image is repeated in drawing ! it’s Qt problem that you can avoid
using the next code.
if isandroid()
setStyleSheet("
border-style: outset;
border-width: 2px;
border-radius: 4px;
border-color: black;
padding: 6px;")
ok
5. Always use Layouts instead of manual setting of controls position and size.
This is the best way to get the expected user interface to avoid problems like (controls with small/extra size)
6. When you deal with Qt Classes you can determine the images from resources (you don’t need to copy them
using main.cpp)
Example:
if isandroid()
mypic = new QPixmap(":/resources/cardsimage")
else
mypic = new QPixmap("cards.jpg")
ok
In the previous example, cards.jpg is added to the resources then we write the “cardsimage” as alias for “cards.jpg”
52.4. Comments about developing for Android using RingQt 525

CHAPTER
FIFTYTHREE
OBJECTS LIBRARY FOR RINGQT APPLICATION
In this chapter we will learn about the objects library for RingQt applications.
Ring comes with the Objects library for RingQt applications. Instead of using global variables for windows objects
and connecting events to objects using the object name, the Objects Library will manage the GUI objects and will
provide a more natural API to quickly create one or many windows from the same class and the library provide a way
to quickly set methods to be executed when an event is ﬁred. Also the library provide a natural interface to quickly
use the parent or the caller windows from the child or sub windows.
The Objects Library is designed to be used with the MVC Design Pattern.
The Objects Library is merged in RingQt so you can use it directly when you use RingQt
53.1 Library Usage
• Use the Open_Window(cWindowControllerClassName) function to open new Windows
• Create at least Two Classes for each window, The Controller Class and the View Class
• Create each controller class from the WindowsControllerParent Class
• Create each view class from the WindowsViewParent Class
• Use the Last_Window() function to get the object of the last window created (The Controller object).
• When you call a sub window, use the SetParentObject() method and pass the self object.
• In the View Class, To determine the event method use the Method(cMethodName) function.
• The Method(cMethodName) function determine the method in the controller class that will be executed.
• Each controller class contains by default the CloseAction() method that you can call to close the window.
• You don’t need to call the Show() Method for each window, When you use Open_Window() It will be called.
• In the view class, Deﬁne the GUI window object as an attribute called win.
• You can use Open_WindowNoShow() to avoid displaying the window.
• You can use Open_WindowAndLink() to quickly get methods to access the windows.
53.2 Example
In the next example we will create two types of windows.
• Main Window contains a button. When the user click on the button a sub window will be opened.
526

• The User Can click on the button many times to open many sub windows.
• Each Sub Window contains Two buttons.
• The ﬁrst button in the sub window change the Main and the Sub Windows Titles.
• The second button in the sub window close the Sub Window.
load "guilib.ring"
new qApp {
open_window( :MainWindowController )
exec()
}
class MainWindowController from WindowsControllerParent
oView = new MainWindowView
func SubWindowAction
Open_window( :SubWindowController )
Last_Window().SetParentObject(self)
class MainWindowView from WindowsViewParent
win = new qWidget() {
SetWindowTitle("Main Window")
btnSub = new qPushButton(win) {
setText("Sub Window")
setClickEvent( Method( :SubWindowAction ) )
}
resize(400,400)
}
class SubWindowController from WindowsControllerParent
oView = new SubWindowView
func SetMainWindowTitleAction
Parent().oView.win.SetWindowTitle("Message from the Sub Window")
oView.win.SetWindowTitle("Click Event Done!")
class SubWindowView from WindowsViewParent
SetWindowTitle("Sub Window")
btnMsg = new qPushButton(win) {
setText("Set Main Window Title")
setClickEvent( Method( :SetMainWindowTitleAction ) )
}
btnClose = new qPushButton(win) {
Move(200,0)
setText("Close")
setClickEvent( Method( :CloseAction ) )
}
resize(400,400)
}
The next screen shot after creating three sub windows.
53.2. Example 527

The next screen shot after clicking on the button in each sub window.
53.2. Example 528

53.3 Open_WindowAndLink() Function
We can use the Open_WindowAndLink() function to connect between the application windows, pass messages (call
methods) between the objects.
This function uses Meta-programming to define dynamic methods in the Caller Class to use the dynamic objects of
other windows that we create.
Example : (Uses the Form Designer)
First Window
1. https://github.com/ring-lang/ring/blob/master/applications/formdesigner/tests/twowindowspart5/firstwindowView.ring
2. https://github.com/ring-lang/ring/blob/master/applications/formdesigner/tests/twowindowspart5/firstwindowController.ring
Second Window
1. https://github.com/ring-lang/ring/blob/master/applications/formdesigner/tests/twowindowspart5/secondwindowView.ring
2. https://github.com/ring-lang/ring/blob/master/applications/formdesigner/tests/twowindowspart5/secondwindowController.ring
53.3. Open_WindowAndLink() Function 529

In the next code for example (from FirstWindowController.ring)
The Open_WindowAndLink() will create an object from the SecondWindowController Class
Then will add the Method : SecondWindow(), IsSecondWindow() Methods to the FirstWindowController Class
Also will add the Method : FirstWindow(), IsFirstWindow() Methods to the SecondWindowController Class
So the SendMessage() method in FirstWindowController class can use the SecondWindow() method to access the
object.
This is more simple than using Last_Window(), Parent() and SetParentObject() methods.
class firstwindowController from windowsControllerParent
oView = new firstwindowView
func OpenSecondWindow
Open_WindowAndLink(:SecondWindowController,self)
func SendMessage
if IsSecondWindow()
SecondWindow().setMessage("Message from the first window")
ok
func setMessage cMessage
oView.Label1.setText(cMessage)
53.4 Objects Library Source Code
The library source code is very simple, You can check the source code ﬁles
• https://github.com/ring-lang/ring/blob/master/extensions/ringqt/objectslib/objects.ring
• https://github.com/ring-lang/ring/blob/master/extensions/ringqt/objectslib/subwindows.ring
53.4. Objects Library Source Code 530

CHAPTER
FIFTYFOUR
USING THE FORM DESIGNER
In this chapter we will learn about using the Form Designer.
We can run the From Designer from Ring Notepad
From the Menubar in Ring Notepad - View Menu - We can Show/Hide the Form Designer window.
Also we can run the Form Designer in another window.
From the Ring Notepad - Tools Menu - Select the Form Designer.
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54.1 The Designer Windows
• Toolbox : To select controls to be added to the window.
• Properties : To set the properties of the active window or controls.
• Design Region : To select, move and resize the window and the controls.
54.2 The Toolbox
We have many buttons.
• Lock : We can use it to draw many controls of the same type quickly.
• Select : We can use it to select a control in the Design Region
• Controls Buttons : Select a control to be added to the window.
54.3 The Properties
• When we select the window or one control, We will have the selected object properties.
• Also In the properties window we have a combobox to select the active control.
• Some properties provide a button next to the property value. We can click on the button to get more options.
• When we select more than one control, We will have options for multi-selection
54.1. The Designer Windows 532

54.4 Running Forms
When we save the form file (*.rform), The Form Designer will create two Ring files
• The Controller Class
• The View Class
For example, if the form file is helloworld.rform
The form designer will generate two files
• helloworldcontroller.ring
• helloworldview.ring
To run the program, Open the controller class file then click the Run button (CTRL+F5)
Tip: When you open a form using Ring Notepad, the controller class will be opened automatically, So we can press
(CTRL+F5) or click on the Run button while the form designer window is active.
54.5 Events Code
1. Just type the method name in the event property.
54.4. Running Forms 533

(2) Then write the method code in the controller class.
54.5. Events Code 534

In this example we write
func CloseWindow
oView.win.close()
Where inside the controller class, We uses the oView object to access the form.
Another Example :
54.5. Events Code 535

The Event Code
func SayHello
oView {
LineEdit2.setText("Hello "+ LineEdit1.text() )
}
54.6 Keyboard Shortcuts
After selecting one or group of controls
• Use the Arrows (Up, Down, Left and Right) to move them around.
• Shift + the Arrows (Up, Down, Left and Right) to Resize the controls.
• Del button to delete the controls.
• CTRL+SHIFT+V to Duplicate the controls.
54.7 Menubar Designer
From the Window properties we can open the Menubar Designer
54.6. Keyboard Shortcuts 536

54.8 Window Flags
From the Window properties we can open the Window Flags window.
54.8. Window Flags 537

54.9 Entering Items
For some controls like the List Widget we can enter items separated by comma ‘,’
54.10 Using Layouts
1. To use layouts, At ﬁrst add the layout control to the window.
2. Use the window “Set Layout” property to determine the main layout.
3. From the layout properties determine the controls and the layout type.
54.11 More Samples and Tests
Check the folder : ring/applications/formdesigner/tests
Online : https://github.com/ring-lang/ring/tree/master/applications/formdesigner/tests
54.9. Entering Items 538

CHAPTER
FIFTYFIVE
SCOPE RULES FOR VARIABLES AND ATTRIBUTES
In this chapter we will learn about scope rules and how Ring find variables.
Also we will learn about conflicts and how to solve/avoid them.
The next information are important once you start developing large applications using Ring
These application may uses
• Global variables (Try to avoid them)
• Classes (Object-Oriented)
• braces { } to access objects
• Declarative Programming
• Natural Programming
55.1 Three Scopes
In Ring we have three scopes :-
1. Public/Global Scope - Each variable you define in the statements part (before functions and classes)
2. Object Scope - When you are inside an object (Inside class method or using { } to access the object )
3. Local Scope - Related to functions and methods
55.2 Defining Variables and Variables Access
1. Ring uses lexical scoping, i.e. the scope of the variable is based on where we defined the variable.
2. Inside braces { } when you access an object, You will change the current active object scope to this object scope
but you still can access the global scope and the local scope.
3. After the ‘Class’ keyword and the class name, when you write variable names to be defined as attributes, You
still can access the global scope.
In this region (class region - after the class name and before methods) we have
• Global Scope —-> The Global Scope
• Object Scope —-> The Object Scope
• Local Scope —-> The Object Scope
539

Note: Since the local scope in the class region point also to the object scope in this region, we can use nested braces
and still have access to the object scope of the class through the local scope.
Tip: You can create windows and controls as attibutes by defining them in this region.
Tip: In the class region if you created objects and used braces {} to access them then using self.attribute inside braces
will use the class (not the object that you access) because you have access to the class through the local scope.
4. Function Parameters are automatically defined in the local scope.
55.3 How Ring find the variable?
1 - Search First in the Local Scope
if not found !
2 - Search in the Object Scope
if not found !
3 - Search in the public scope
if not found —-> Runtime Error
if found —-> Check if we can do optimization to avoid searching next time (Cache / Pointers for performance).
55.4 Using Object.Attribute
When we use object.attribute the search will be in the object attributes only.
I.e. no search will be done in the local scope or in the global scope for the object attribute.
Note: Using self.attribute will search for the first self before searching for attributes.
55.5 The Self Object
The self object is a reference to the current object that we can use from the class methods.
When we are inside class method and use Self we mean the object that will be created from this class.
Inside the class methods if we used Braces { } this will change the current object scope and self will be changed also
inside braces to reference the object that we access using Braces.
Inside the Class Region (after the class name and before any method) we have access to the object through the object
scope and the local scope also. In this region using Self will always be a reference to the class object. if we used
Braces to change the object scope then used Self inside Braces, Also self will be a reference to the class object (not
the object that we already access using braces) because in the class region we have :-
• Global Scope —> Global Scope
• Object Scope —> Object Scope
55.3. How Ring find the variable? 540

• Local Scope —> Object Scope
And using Braces changes the object scope only (not the local scope) and when Ring search for variables it will search
in the Local Scope first so it will find self in the class that we are inside.
55.6 How Ring Define Variables and Attributes
Ring will use the variable name in the Assignment operation
1 - Search using the variable name
2 - If not found —> Avoid the runtime error and define the variable in the current scope
3 - If found —> Use the variable and don’t define anything in the current scope
• In the global region (before any function or class) the current scope is the global scope.
• In the class region (after the class name and before any method) the current scope is the object attributes.
• In Functions and methods the current scope is the local scope.
55.7 Conflict between Global Variables and Class Attributes
Look at this example:
name = "test"
o1 = new person
see o1
class person
name
address
phone
In the previous example we have a global variable called ‘name’ inside the class person.
when we use the variable ‘name’, Ring will start the search operation and will try to find it.
if found —> Use it
if not found —> Define new attribute
But the variable name is a global variable, so it will be found and used!
We will not have the attribute name! added to the object.
Solution (1) - Use the Main Function
func main
name = "test"
o1 = new person
see o1
class person
name
address
phone
Solution (2) - Use special mark for global variable names like $
55.6. How Ring Define Variables and Attributes 541

$name = "test"
o1 = new person
see o1
class person
name
address
phone
Solution (3) - Use the AddAttribute() Method
name = "test"
o1 = new person
see o1
class person
AddAttribute(self,"name")
address
phone
Solution (4) - Use self before the attribute name
name = "test"
o1 = new person
see o1
class person
self.name
address
phone
So what is the best solution to this conflict?
1 - Use the $ Mark for global variables
2 - Optional : Try to avoid global variables and use the Main function
In practice i do both of them.
The other solution
• Use self before the attribute name or use AddAttribute()
55.8 Conflict between Class Attributes and Local Variables
This conflict may happen when we access the object using braces
Example:
func main
name = "nice"
o1 = new person {name="mahmoud" address="Egypt" phone = 000 }
see o1
class person
name
address
phone
55.8. Conflict between Class Attributes and Local Variables 542

In the previous example we have the local variable name.
The value of this variable will be set to “mahmoud” instead of the object attribute.
Solution (1) : Just use Self
func main
name = "nice"
o1 = new person {self.name="mahmoud" address="Egypt" phone = 000 }
see o1
class person
name
address
phone
Solution (2) : Change the Local variable name
func main
cName = "nice"
o1 = new person {name="mahmoud" address="Egypt" phone = 000 }
see o1
class person
name
address
phone
Solution (3) : Change Braces and use the Dot operator
func main
name = "nice"
o1 = new person
o1.name ="mahmoud"
o1.address ="Egypt"
o1.phone = 000
see o1
class person
name
address
phone
55.9 Using Braces to access objects inside Class Methods
Remember that we have Three scopes (Local Scope, Object Scope and Global Scope) and when we are inside a class
method, we expect that we have access to the object attributes and methods and this is true until we use braces to
access another object attributes and methods because in this case our object scope will be switched to another object.
new point { test() }
class point
x=10 y=20
func test
see x + nl + y + nl # works fine
myobj = new otherclass {
see name + nl
see x + nl + y + nl # error !
55.9. Using Braces to access objects inside Class Methods 543

}
class otherclass
name = "test"
Output:
10
20
test
Line 8 Error (R24) : Using uninitialized variable : x
In method test() in file methodbraceerror.ring
called from line 5 in file methodbraceerror.ring
Now what we will do to solve the previous problem?
Solution (1) : Write the code that access the class attributes outside braces.
class point
x=10 y=20
func test
see x + nl + y + nl # works fine
see name + nl
}
see x + nl + y + nl # Outside braces - works fine
class otherclass
name = "test"
Output:
10
20
test
10
20
Solution (2) : Don’t Use Braces
class point
x=10 y=20
func test
see x + nl + y + nl
myobj = new otherclass
see myobj.name
see x + nl + y + nl
class otherclass
name = "test"
Solution (3) : Copy the self object
We may use this solution if we want to use braces and get access to the class attributes (Just Reading).

class point
x=10 y=20
func test
oSelf = self
see x + nl + y + nl
see name + nl
see oself.x + nl + oself.y + nl
}
class otherclass
name = "test"
Output:
10
20
test
10
20
Now look at this line
oself = self
The problem with the previous line is that we will have a new copy from the object Because in Ring the assignment
operator copy lists and objects by value (not by reference).
When we access the new object attributes (reading) we don’t have problems
But if we modiﬁed the object attributes (Then we will modify the copy!).
Note: We can use braces again with the copy
class point
x=10 y=20
func test
oSelf = self
see x + nl + y + nl
see name + nl
oSelf {
see x + nl + y + nl
}
}
class otherclass
name = "test"
In a GUI application, we may create a class contains the window objects as attributes to be able to access the controls
from different methods. Remember the previous information when you try to access objects using braces inside
methods because in this case you can’t access the object attributes directly and if you copied the self object you will
work on a copy and the new controls that you create will be related to the copy and you can’t access them.

55.10 Accessing the class attributes from braces inside class meth-
ods
We access the class attributes directly from the class methods, also we have the choice to use the Self reference before
the attribute/method name. Using Braces {} inside class method change the active object scope and prevent us from
getting direct access to the class attributes. Also using Self will not help because the Self reference will be changed to
the object that we access using Braces.
In this case if you want to read an attribute you have to copy the Self object before using Braces and if you want to
modify an attribute you have to the copy from local variable to the object attribute after using Braces.
This case happens when you want to read/modify attribute insead braces.
Class MyApp
oCon # Attribute
# some code here
Func OpenDatabase
# some code here
new QSqlDatabase() {
oCon = addDatabase("QSQLITE") {
setDatabaseName("weighthistory.db")
open()
}
}
self.oCon = oCon
# some code here
In the previous example we want to create the connection object and save it inside the oCon attribute.
The object is an output from the addDatabase() method that we use after accessing the QSQLDatabase() object.
Inside braces we can’t use the Self reference to use the object created from the MyApp class, Because the Self reference
here will be to the object that we access using Braces.
We solved the problem in the previous example by creating a local variable called oCon then after Braces we copied
that variable to the oCon attribute.
The next code is another solution.
Class MyApp
oCon # Attribute
# some code here
Func OpenDatabase
# some code here
oCon = new QSqlDatabase()
oCon = oCon.addDatabase("QSQLITE") {
Open()
}
# some code here
The next code is a better solution.
55.10. Accessing the class attributes from braces inside class methods 546

Class MyApp
oCon # Attribute
# some code here
Func OpenDatabase
# some code here
new QSqlDatabase() {
this.oCon = addDatabase("QSQLITE") {
Open()
}
}
# some code here
Note: We used this.attribute to access the class attribute (oCon) while we are inside Braces.
55.11 Creating a Class for each Window in GUI applications
A good way for creating classes for windows is to deﬁne the window directly after the class name
In this area you can use nested braces without problems to deﬁne the window and the controls, and they will be
attributes that you can access from methods.
Example:
Load "guilib.ring"
new qApp
{
$ObjectName = "oFirstWindow"
oFirstWindow = new FirstWindow
$ObjectName = "oSecondWindow"
oSecondWindow = new SecondWindow
exec()
}
Class FirstWindow
setgeometry(0,50,300,200)
setWindowTitle("First Window")
label1 = new qLabel(win)
{
setgeometry(10,10,300,30)
setText("0")
}
btn1 = new qPushButton(win)
{
move(100,100)
setText("Increment")
setClickEvent($ObjectName+".increment()")
}
55.11. Creating a Class for each Window in GUI applications 547

The Ring programming language version 1.4 book - Part 19 of 30

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The Ring programming language version 1.4 book - Part 19 of 30