delphi – FireDac冻结GUI

下面的代码示例显示了从MSSql Server中检索记录的一种方法
在使用FireDAC的后台线程中.这省略了一些细节.例如,在实践中,而不是TQueryThreads Execute只打开一次然后终止查询,你可能希望线程的Execute包含一个while循环,在调用Synchronize之后它在信号量上等待,然后关闭/重新打开查询以根据需要随时更新主线程.

type

  TForm1 = class;

  TQueryThread = 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 Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  public
    QueryThread : TQueryThread;
  end;

[...]

constructor TQueryThread.Create(AForm : TForm1);
begin
  inherited Create(True);
  FreeOnTerminate := True;
  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 TQueryThread.Destroy;
begin
  FQuery.Free;
  FConnection.Free;
  inherited;
end;

procedure TQueryThread.Execute;
begin
  Query.Open;
  Synchronize(TransferData);
end;

procedure TQueryThread.TransferData;
begin
  Form.FDQuery1.DisableControls;
  Form.FDQuery1.Data := Query.Data;
  Form.FDQuery1.EnableControls;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  QueryThread.Resume;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  QueryThread := TQueryThread.Create(Self);
end;

MJN关于书签的评论告诉你如何保留gui中的当前数据行位置.

顺便说一下,虽然我经常用TClientDataSets做到这一点,把这个答案放在一起是我第一次尝试使用FireDAC.在配置组件方面,我所做的只是将组件拖离Palette,按照您的预期将它们“连接在一起”,然后设置FDConnection的Params和FDQuery的Sql.