Re: Detecting if changes have been made

Posted by webmaster Guido on August 22, 2002 at 05:35:19:

In Reply to: Detecting if changes have been made posted by P12256 + Lesley on August 21, 2002 at 06:41:12:

: 1. Where a file has been opened and the user clicks on File Save - how can I get it to save to the file without displaying the File Save As Dialog box yet ask for a filename when the file is new?

: 2. Detect if the contents of a list box have changed or had new entries added to it and if true, then ask the user if they want to save the changes when they select File Exit
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1A. Declare a global string variable that contains the filename:

var TheFile: string;

1B. At program start, set TheFile to an empty string:

TheFile := '';

1C. Before saving to a file, check variable TheFile. If it's empty, show a secondary form, containing an edit box called edFileName and a button. The user enters the filename; next, he clicks the button, and that closes the form.

if Length(TheFile) = 0 then begin
  Form2.ShowModal; // form stays open until button clicked
  TheFile := Form2.edFileName.Text;
end;
if Length(TheFile) = 0 then
  ShowMessage('Not saved. Need a filename.');
else
  // ...set up the entire path and save the file
  // e.g.: save under the name
  // 'C:\Results' + TheFile + '.txt'

This is still quite basic: even if TheFile is not empty, you should check if it is valid. For example, it can not be only spaces.

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2. Simply checking if there are items added is easy: store the number of items at in an integer variable OldNumber program start, and after each saving of the file:

OldNumber := Listbox1.Items.Count;

Before exiting the program, compare the number of items with OldNumber.

But... if you want to save also when the *contents* of (one ore more) item(s) is changed, it is more complicated. You need a backup copy of all the listbox items, for comparing with the current listbox before exiting. You can use a TStringList for this:

var OldList: TStringList;

At program start:

OldList := TStringList.Create;

After each save, copy the items:

OldList.Clear;
for i := 0 to ListBox1.Items.Count - 1 do
  OldList.Add(ListBox1.Items[i]);

Before exiting, compare the lists:

var SaveIt: Boolean;
  ...
  SaveIt := ListBox1.Items.Count <> OldList.Items.Count;
  if (not SaveIt) and (ListBox1.Items.Count > 0) then 
    for i := 0 to ListBox1.Items.Count - 1 do begin
      SaveIt := ListBox1.Items[i] <> OldList.Items[i];
      if SaveIt then break;
    end;
  if SaveIt then
    // ...save the file...

Don't forget, at program end, to free the TStringList:

  OldList.Free;

This is because OldList is an *object* that you created, so you must destroy it in order to have no "memory leaks".

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