Object-oriented Software in Ada 95

Packages as classes 87
The Ada specification of the class TUI is:
package Class_TUI is
type Menu_Item is ( M_1, M_2, M_3, M_4, M_Quit );
type TUI is private;
procedure Menu( The:in out TUI; M1,M2,M3,M4:in String );
function Event( The:in TUI ) return Menu_Item;
procedure Message( The:in TUI; Mes:in String );
procedure Dialog(The:in TUI; Mes:in String; Res:out Float);
procedure Dialog(The:in TUI; Mes:in String; Res:out Integer);
private
-- Not a concern of the client of the class
end Class_TUI;
For example, if an instance of the TUI had been declared with:
Screen : TUI;
then, to setup the menu system:
[a] Print
[b] Calculate
Input selection:
the following code sequence would be used:
Menu( Screen, "Print", "Calculate", "", "" );
Note:
Null or empty menu items are not displayed.
A string may be of any length. However, to store a string the receiving object must be of the correct
size. Ada strings are fully discussed in Section 8.8.
The user’s response to this menu is elicited with the function event. The function event returns an
enumeration representing the menu item selected. For example, if the user selected option [b] then the code:
case Event( Screen ) is
when M_1 =>
when M_2 =>
--Print
--Calculate
associated with label M_2 would be obeyed.
Note:
The selected menu item is indicated by an enumeration M_1 for menu item 1, M_2 for menu item 2, etc.
A programmer can display a message onto the TUI by using the procedure message which has the text to be
output as its second parameter. Likewise, a programmer can initiate a dialog with the user by using the procedure
dialog that returns a floating point number. The TUI currently only supports dialogs that solicit a floating point
number or integer number.
The fragment of code below illustrates the use of message and dialog interactions in a program which converts
miles to kilometres.
Message( Screen, "Distance converter" );
Dialog ( Screen, "Enter distance in miles", Miles );
Message( Screen, "Distance in Kilometres is " &
Float'Image( Miles * 1.6093 ) );
Note:
The operator & concatenates two strings into a single string. For example, "Hello" & " " &
"world" delivers the single string "Hello world".
© M A Smith - May not be reproduced without permission