delphi - 在 Delphi 中获取 Advantage 数据库查询的进度

Question

我找了又找，但没有找到如何在Delphi中获取查询的进度。我找到了有关 Advantage .NET 数据提供程序的一些信息，但可以使用 Delphi 的一些帮助。

Answer 1

您想要AdsRegisterCallbackFunction方法。这是我用来显示为 TAdsTable 创建索引期间的进度的一个简单示例；它的工作方式与 TAdsQuery 中的进度完全相同:

implementation

var
  // Holder for reference to progressbar on form, so it can be
  // accessed easily from  the callback - see below
  PB: TProgressBar = nil;  


// replacement for Application.ProcessMessages, since we don't have 
// access to the Application from the callback either

procedure KeepWindowsAlive;
var
  M: TMsg;
begin
  if PeekMessage(M, 0, 0, 0, pm_Remove) then
  begin
    TranslateMessage(M);
    DispatchMessage(M);
  end;
end;

// The callback function itself - note the stdcall at the end
// This updates the progressbar with the reported percentage of progress
function ProgressCallback(Percent: Word; CallBackID: LongInt): LongInt; stdcall;
begin
  if PB <> nil then
    PB.Position := Percent;
  KeepWindowsAlive;
  Result := 0;
end;

// The button click handler. It registers the callback, calls a function 
// that creates the index (not shown here), and then unregisters the callback.
//
// As I mentioned above, it works the same way with a TAdsQuery.
// You'd simply assign the SQL, set any params, and register the
// callback the same way. Then, instead of calling my CreateIndexes
// method, you'd Open the query; it will call the progress callback
// periodically, and when the query finishes you just unhook the
// callback as shown here.
procedure TCreateIndexesForm.CreateButtonClick(Sender: TObject);
begin
  // Grab a reference to the progress bar into the unit global, so we don't
  // need a reference to the form by name in the callback.
  PB := Self.ProgressBar1; 

  // AdsTable is a property of the form itself. It's set
  // during the constructor. It's just a `TAdsTable` instance.
  // The index info is set in that constructor as well (tag, 
  // expression, type, etc.).
  AdsTable.AdsRegisterCallbackFunction(@ProgressCallBack, 1);
  try
    CreateIndexes;
  finally
    // Unhook the progress callback
    AdsTable.AdsClearCallbackFunction;
    // Clear the outside reference to the progress bar
    PB := nil;
  end;
end;

请注意，回调必须是独立过程(如上所示)，而不是表单方法。我展示了一种方法，通过使用进度条的单元全局引用，不必硬编码对特定表单名称的访问。