Ofline
Remarks This FireDAC example, and the others I'm planning to submit, will avoid the use of native calls to asynchronously open the dataset. Examples FireDAC example The code sample below shows one way to retrieve records from an MSSql Server in a background thread using FireDAC. Tested for Delphi 10 Seattle As written: The thread retrieves data using its own TFDConnection and TFDQuery and transfers the data to the form's FDQuery in a call to Sychronize(). • The Execute retrieves the data only once. It could be altered to run the query repeatedly in response to a message posted from the VCL thread.
Код:
type
TForm1 = class;
TFDQueryThread = class(TThread)
private
FConnection: TFDConnection;
FQuery: TFDQuery;
FForm: TForm1;
published
constructor Create(AForm : TForm1);
destructor Destroy; override;
procedure Execute; override;
procedure TransferData;
property Query : TFDQuery read FQuery;
property Connection : TFDConnection read FConnection;
property Form : TForm1 read FForm;
end;
TForm1 = class(TForm)
FDConnection1: TFDConnection;
FDQuery1: TFDQuery;
DataSource1: TDataSource;
DBGrid1: TDBGrid;
DBNavigator1: TDBNavigator;
Button1: TButton;
procedure FormDestroy(Sender: TObject);
procedure Button1Click(Sender: TObject);
procedure FormCreate(Sender: TObject);
private
public
QueryThread : TFDQueryThread;
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
{ TFDQueryThread }
constructor TFDQueryThread.Create(AForm : TForm1);
begin
inherited Create(True);
FreeOnTerminate := False;
FForm := AForm;
FConnection := TFDConnection.Create(Nil);
FConnection.Params.Assign(Form.FDConnection1.Params);
FConnection.LoginPrompt := False;
FQuery := TFDQuery.Create(Nil);
FQuery.Connection := Connection;
FQuery.SQL.Text := Form.FDQuery1.SQL.Text;
end;
destructor TFDQueryThread.Destroy;
begin
FQuery.Free;
FConnection.Free;
inherited;
end;
procedure TFDQueryThread.Execute;
begin
Query.Open;
Synchronize(TransferData);
end;
procedure TFDQueryThread.TransferData;
begin
Form.FDQuery1.DisableControls;
try
if Form.FDQuery1.Active then
Form.FDQuery1.Close;
Form.FDQuery1.Data := Query.Data;
finally
Form.FDQuery1.EnableControls;
end;
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
QueryThread.Free;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
if not QueryThread.Finished then
QueryThread.Start
else
ShowMessage('Thread already executed!');
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
FDQuery1.Open;
QueryThread := TFDQueryThread.Create(Self);
end;
end.
Read Retrieving updated TDataSet data in a background thread online