Emptying string grid in Delphi

Question

In Delphi, is there a fast way of emptying a TStringgrid (containing in excess of 5000 rows) that will also free the memory?

Setting the rowcount to 1, empties the grid but does not free the memory.

Thanks in advance,

Paul

Answer 1

This should uninitialize the allocated strings (from the string list where the row texts are stored). Cleaning is done by columns since you have a lot of rows.

procedure TForm1.Button1Click(Sender: TObject);
var
  I: Integer;
begin
  for I := 0 to StringGrid1.ColCount - 1 do
    StringGrid1.Cols[I].Clear;
  StringGrid1.RowCount := 1;
end;

Answer 2

By "does not free the memory", do you mean that if you set RowCount := 1 , and then set the RowCount := 10' you can still see the old content of the Cells`?

If so, this is an old issue and has nothing to do with the memory not being freed; it's simply because you just happen to see the previous content of the memory when it's allocated again, because memory isn't zero'd out.

I have a pretty standard routine in a utility unit that deals with this visual glitch, and unless the grid is huge works fast enough. Just pass the TStringGrid before you change the RowCount or ColCount to a lower value.

procedure ClearStringGrid(const Grid: TStringGrid);
var
  c, r: Integer;
begin
  for c := 0 to Pred(Grid.ColCount) do
    for r := 0 to Pred(Grid.RowCount) do
      Grid.Cells[c, r] := '';
end;

Use it like this:

ClearStringGrid(StringGrid1);
StringGrid1.RowCount := 1;

Answer 3

我建议将您的字符串值存储在您可以完全控制的自己的内存中，然后使用 TDrawGrid 或更好的虚拟 TListView 来根据需要显示该内存的内容。

Answer 4

The fastest way to use a TStringGrid is using OnGetValue/OnSetValue. This way only the text of visible cells are requested dynamically. Adding and removing rows is then lighting fast, otherwise TStringgrid is very slooow when you have more than 5000 records. This way I can fill and clear a grid with 700.000 records within a second!

Answer 5

When memory usage is the critical argument, consider using another grid. For example, NLDStringGrid that is (re)written by myself, and which has an additional property called MemoryOptions . It controls whether data can be stored beyond ColCount * RowCount , whether the storage is proportional (less memory usage for partially filled rows and columns), whether to store the Cols and Rows property results and whether the data is stored in sparse manner.

To clear such grid that has moBeyondGrid excluded from the memory options, setting RowCount to FixedRows suffices.

It's open source and downloadable from here .