LMDGrid columns clear question.

Carlo Marangoni

I have tried two different methods for clearing or emptying a grid. The first one was a loop, deleting each row one at a time (This was notably slow). The second one was 

calling on the column.clear; in which it did indeed clear it very fast. Then I recreated the columns in code. The problem with the second method was, even though it repopulated the grid, when selecting a row I would get all sorts of errors. 

What else does the column.clear; also effect besides removing the headers? Is there a proper way to clear the row - column data that does not require deleting each row one at a time?

Eugene Balabuev (LMD)

You can assing zero to Grid.DataRowCount property:

MyGrid.DataRowCount := 0;

Carlo Marangoni

I am already doing this.

for RowDelete := 0 to ContactsGrid.DataRowCount -1 do

ContactsGrid.DeleteDataRow(RowCount);

But it is slow compared to Grid.column.clear;

Carlo Marangoni

I checked what the column count is after doing columns clear, and it reports back as zero. I thought a first that it was only clearing the data

under the columns including the header information. I also thought that by recreating the columns, I was duplicating what was already there

but not visible. So I have verified that both the columns and row are 0. So I feel that I need to reinitialize the grid component before I insert the new columns, this part I am not sure how to do this.

Carlo Marangoni

Here is more on the code.

procedure TContactsForm.GridCreate();

Var

cn1, cn2, cn3, cn4, cn5: TLMDGridTextColumn;

Begin

ContactsGrid.Columns.Clear;

  cn1 := TLMDGridTextColumn.Create(Self);

  cn1.Title.Caption := 'ID';

  cn1.Width := 30;

  ContactsGrid.Columns.Add(cn1);

  cn2 := TLMDGridTextColumn.Create(Self);

  cn2.Title.Caption := 'Company';

  cn2.Width := 100;

  ContactsGrid.Columns.Add(cn2);

  cn3 := TLMDGridTextColumn.Create(Self);

  cn3.Title.Caption := 'First Name';

  cn3.Width := 85;

  ContactsGrid.Columns.Add(cn3);

  cn4 := TLMDGridTextColumn.Create(Self);

  cn4.Title.Caption := 'Last Name';

  cn4.Width := 100;

  ContactsGrid.Columns.Add(cn4);

  cn5 := TLMDGridTextColumn.Create(Self);

  cn5.Title.Caption := 'Phone Number';

  cn5.Width := 50;

  ContactsGrid.Columns.Add(cn5);

refreshGrid // this repopulates the grid

showmessage('Column Count' + inttostr(ContactsGrid.columns.Count) + 'Row Count' + inttostr(ContactsGrid.DataRowCount))

End;

So what I have noticed is I can recreate the columns as many times as I need, but once a row is selected and recreate the columns it does not create all the columns. The first refresh on a selected row doesn't create the ID column and produces an appropriate error, and then the company column until no columns are created.

Carlo Marangoni

Ok last question what is the best method on removing or deleting a grid column?

Eugene Balabuev (LMD)

If you want to delete a column, you can do it like this:

MyGrid.Columns[MyColumnIndex].Free;

But, if you simply want to refresh the grid data, then you do not need to clear and recreate columns. As I answered to you previously, to clear grid data you can use DataRowCount property:

MyGrid.DataRowCount := 0;

Carlo Marangoni

Thanks for the reply, This is helpful. I started going down a rabbit hole with reusing the grid for various other reasons with in my app.

I will try this today.