FindField (Delphi)

Description

This example uses a button to copy the value of a field of the previous record into the corresponding field of the current record. The field to copy is specified by using FindField and the name of the field.

Code

procedure TForm1.Button1Click(Sender: TObject);
var
   SavePlace: TBookmark;
   PrevValue: Variant;
begin
  Close;
   with Customers do
   begin
    { Get a bookmark so that you can return to the same record. }
    SavePlace := GetBookmark;
    try
      { Move to previous record. }
      FindPrior; 
      { Get the value. }
      { This is the safe way to get the 'CustNo' field. }
      PrevValue := FindField('Field2').Value;
      { This is not the safe way to change the 'CustNo' field. }
//    PrevValue := Fields[1].Value;
      { Move back to the bookmark.
      This may not be the next record anymore,
      if something else is changing the dataset asynchronously. }
      GotoBookmark(SavePlace);
      { Set the value. }
      Edit;
      { This is the safe way to change the 'CustNo' field. }
      FindField('Field2').AsString := PrevValue;
      { This is not the safe way to change the 'CustNo' field. }
//      Fields[1].AsString := PrevValue;
      { Free the bookmark. }
    finally
      FreeBookmark(SavePlace);
    end;
  end;
end;

{
To ensure that the button is disabled when there is no
previous record, the OnDataChange event of the DataSource
detects when you move to the beginning of the file (BOF
property becomes True) and disables the button. Detection
occurs on scrolling and editing, not on selection with the mouse.
procedure TForm1.DS2DataChange(Sender: TObject; Field: TField);
begin
  if Customers.Bof then
    Button1.Enabled := False
  else
    Button1.Enabled := True;
end;

Uses

• Data.DB.TDataSet.FindField ( fr | de | ja )
• Data.DB.TField.AsString ( fr | de | ja )
• Data.DB.TDataSource.OnDataChange ( fr | de | ja )