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INPUT & OUTPUT
An integral property of computer hardware is the idea of input, processing
and output - this is also used in software. When getting input
variables are often used.
Input is usually done using the following
components:
Edit
RichEdit
Memo
RichEdit
MaskEdit
StringGrid
Output is usually done using the following components:
Label
Panel
Memo
ListBox
RichEdit
StringGrid
Input and output from windows created during runtime
a) ShowMessage
• This calls up a small window that can be used to give the user extra
information.
• The only parameter (value typed in by programmer) is the message that
needs to be displayed.
• It usually uses the name of the project file as form caption.
• An example of coding would be:
ShowMessage('This is a ShowMessage!');
b) InputBox
• This dialog box allows the user to enter data that can be used in the
program.
• The coding for an InputBox requires the following:
StringResult := InputBox(‘Window caption, ‘Prompt’, ‘Default value’);
• For example to enter data into the string variable sName and then
transfer this to a label:
procedure
TForm1.Button1Click(Sender: TObject);
var
sName : string;
begin
sName := InputBox('Name', 'Enter your name', '');
lblName.Caption := sName;
end;
c) MessageDlg (Message Dialog box)
• Message Dialog boxes are used to provide the user with certain options
or warnings and let the user then accept the message or make decision.
• This is often used to display errors or ask whether a user wants to save
a file or exit the program or not.
• The code structure for a MessageDlg:
MessageDlg(StringDisplayed, MessageType, Buttons, HelpTopic);
• Here are three examples of the usage of the MessageDlg:
MessageDlg('Invalid input!', mtWarning, [mbOK],0);
if MessageDlg('This is an error', mtError,
[mbOK, mbAbort],0) = mrOK then
lblOutput.caption := 'User pressed OK'
else
lblOutput.caption := 'User pressed Abort';
if MessageDlg('Do you want to exit',
mtConfirmation, [mbYes, mbNo],0) = mrYes then
Application.Terminate; {Close form with Form1.Close}
Message types: mtWarning, mtError,
mtInformation, mtConfirmation, mtCustom.
Button types: mbYes, mbNo, mbCancel, mbHelp, mbAbort, mbRetry, mbIgnore,
mbAll. (There are also groupings such as: mbYesNoCancel, mbOKCancel and
mbAbortRetryIgnore.)
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