Page Comparison

...

This script creates a button, with the text "Hello world!" inside a window. When you click this button a new information window will pop up, saying "Hello World!" and displaying a OK button.

...

set w [qwidget ]

A window in QTcl is an instance of a QWidget object, hence the command name. It may be followed by a list of flags. Although rarely used, the flags can be used to modify the widgets look and behaviourbehavior. The next statement tells QTcl to delete the widget from memory when it is closed:

qsetattribute deleteonclose

...

qsetwindowtitle "Hello"

The qsetwindowtitle command sets the window title. While there may be several windows available, QTcl will simply apply the command to the most recently created widget, which in this case is the QWidget window. The most recently created widget is also the so-called current widget. It does not matter whether the widget is visible or not. This is in fact how most Qt commands work.

...

qvboxlayout {
	
}

The qvboxlayout command creates a layout manager for the window. A layout manager is also known as a geometry manager. The task of the layout manager is to arrange the widgets in a particular order. For instance, the QVBoxLayout layout manager stacks widgets vertically in their order of creation. There are two other layout managers in QTcl:

...

qpushbutton "Hello world!"

The command qpushbutton creates the conventional button found in user interfaces. There are several types of buttons available in QTcl. Right now this button only has one argument which is the button text. Thus we need a second argument to tell the button what to do when being clicked.

...

qinformation Information "Hello world!"

...

So far we have created the window and the button in memory. No window is yet visible on the screen. To make the window visible we have to invoke the final qshow command.

qshow $w

QTcl will then draw the most recently created widget, or current widget, on to the screen. In this case the current widget is the window, which is then displayed along with its contents.

...

# Create toplevel window
set w [qwidget ]

# Delete window from memory when closing
qsetattribute deleteonclose

qsetwindowtitle "Hello"

# Arrange contents vertically
qvboxlayout {
	# Create a button that show an information dialog when pushed
	qpushbutton "Hello world!" { qinformation Information "Hello world!" }
}

# Make window visible
qshow $w

While this script is short, it has illustrated several key features of QTcl programming. For example, all QTcl commands begin with the letter 'q'. This serves the purpose of setting QTcl commands apart from the built-in Tcl commands. Also, several commands are located inside the '{...}' delimited block that follows the qvboxlayout statement. This syntactical structure tells QTcl that all widgets enclosed in the '{...}' block should be treated according to the enclosing command, in this case qvboxlayout. Moreover, since the QVBoxLayout is owned by the toplevel window, all widgets created inside this layout manager are also made child widgets of this window.