ListBox.Items.Add is slow and flickers

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Adding a (larger) group of entries to a ListBox is very slow,
because after every "items.add" call the ListBox is repainted.

There are two ways to overcome this:

• use the Windows message WM_SETREDRAW (see Win32.hlp for details).
  The VCL provides two methods for this: BeginUpdate and EndUpdate.
  I would assume that this is faster than method #2.
• read the strings in a temporary TStringList object.
  Maybe you already have such a list - in this case you should use your existing list.
  Then use the Assign method to transfer the whole list.

	// method #1 procedure TForm1.Button1Click(Sender: TObject); var i : integer; begin ListBox1.Items.BeginUpdate; for i:=1 to maxitems do ListBox1.Items.add(IntToStr(i)); ListBox1.Items.EndUpate; end; // method #2 procedure TForm1.Button2Click(Sender: TObject); var i : integer; tmp: tstringlist; begin tmp:=TStringList.Create; for i:=1 to maxitems do tmp.add(inttostr(i)); ListBox1.Items.Assign(tmp); tmp.Free; end;

Comments:

2007-02-16, 05:08:27

anonymous from Lithuania

aa

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