ClientDataSet1加载数据，统计事件错误：ClientDataSet1: Dataset not in edit or insert mode.

先从数据库加载数据
First;
while not Eof do
begin
ClientDataSet1.Append;
ClientDataSet1.FieldByName('bh').AsString:=FieldByName('bh').AsString;
ClientDataSet1.FieldByName('qm').AsString:=FieldByName('qm').AsString;
ClientDataSet1.FieldByName('dw').AsString:=FieldByName('dw').AsString;
ClientDataSet1.FieldByName('sl').AsString:=FieldByName('sl').AsString;//数量
ClientDataSet1.FieldByName('bz').AsString:=FieldByName('bz').AsString;
ClientDataSet1.Post;
Next;
end;

然后 ClientDataSet1slChange 事件里统计数量和
procedure TFormScmbAdd.ClientDataSet1slChange(Sender: TField);
var
a:double;
begin
a:=0;
if ClientDataSet1.IsEmpty then Exit;
if (ClientDataSet1.FieldByName('sl').isnull) or (ClientDataSet1.FieldByName('sl').asString='') then exit;
ClientDataSet1.First;//去掉这句就没有错误，但去掉后就统计不出来
while not ClientDataSet1.Eof do
begin
a:=a+strtoint(ClientDataSet1.FieldByName('sl').AsString);
ClientDataSet1.Next;
end;
Label5.Caption:=floattostr(a);
end;