Interactive dialogs or How to let user decide
Sometimes we need to ask the user for data or inform him about something. In that case we need an interactive dialog.
The simplest one is ShowMessage(const Msg: String) procedure that takes a string and displays it as a small popup window with OK button.
ShowMessage('That''s a message for you!');
If we know that the string might contain unicode characters we need to use WideShowMessage(const Msg: WideString) procedure instead.
There are several dialogs to ask user for data. The most representative functions are:
|function DialogYesNo(const Msg: String): Boolean;|
|function InputQuery(const ACaption, APrompt: String; var Value: String): Boolean;|
DialogYesNo function takes a message string and lets user to choose between YES and NO buttons to click. It returns TRUE if YES was choosen and FALSE otherwise.
begin if DialogYesNo('This filename "'+FileName+'" looks bad.'+#13+ 'I would prefer to name that file "Very Important File.txt". '+#13#13+'Do you agree?') then FileName := 'Very Important File.txt'; end.
The code above shows two important things about string constants. First is that you need to use #13 (or #10 or #13#10) to break the line. And second that you need to escape every ' by doubling it (''). So if you want to start a string constant with ' you will need three of them ''' !
InputQuery is the most powerful dialog. It takes two string constants (a caption of the popup window and a prompt, in which you can explain what kind of data you are expecting from user). The third parameter is a string variable Value that will return user text input. The current content of the Value variable is displayed in the input text box as the default value.
var Value: String; begin Value := 'Meaningless filename.txt'; InputQuery('Incorrect filename', 'I am not able to produce any meaningful filename!'+ ' Would you mind giving it manually?', Value); FileName := Value; end.