在Delphi中获取Advantage数据库查询的进度

Question

我已经搜索和搜索，但无法找到如何在Delphi中获取查询的进度。我找到了有关Advantage .NET数据提供者的一些信息，但可以在Delphi中使用一些帮助。

Answer 1

你想要AdsRegisterCallbackFunction方法。下面是一个用于在创建TAdsTable索引期间显示进度的简单示例;它的工作原理完全一样的方式进步的TAdsQuery：

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; 

注意回调必须是一个独立的程序（如上图所示），而不是形式的方法。我已经展示了一种不必通过使用进度条的单位全局引用来硬编码访问特定表单名称的方法。