2

I'm trying to show an information message and an animated gif (an Hourglass) while my application is busy (loading a query).

I have defined a Form to show that Message (using the code shown in this post: How to use Animated Gif in a delphi form). This is the constructor.

constructor TfrmMessage.Show(DisplayMessage: string); begin inherited Create(Application); lblMessage.Caption := DisplayMessage; // Set the Message Window on Top SetWindowPos(Handle, HWND_TOPMOST, 0, 0, 0, 0, SWP_NoMove or SWP_NoSize); Visible := True; // Animate the HourGlass image (imgHourGlass.Picture.Graphic as TGIFImage).Animate := True; Update; end;

The problem is that the animated Gif remains still while the main thread is busy (loading the query).

I have tried drawing manually the animation on a separate thread.

type TDrawHourGlass = class(TThread) private FfrmMessage: TForm; public constructor Create(AfrmMessage: TForm); procedure Execute; override; procedure ShowFrame1; procedure ShowFrame2; procedure ShowFrame3; procedure ShowFrame4; procedure ShowFrame5; end; constructor TDrawHourGlass.Create(AfrmMessage: TForm); begin inherited Create(False); FfrmMessage := AfrmMessage; end; procedure TDrawHourGlass.Execute; var FrameActual: integer; begin FrameActual := 1; while not Terminated do begin case FrameActual of 1: Synchronize(ShowFrame1); 2: Synchronize(ShowFrame2); 3: Synchronize(ShowFrame3); 4: Synchronize(ShowFrame4); 5: Synchronize(ShowFrame5); end; FrameActual := FrameActual + 1; if FrameActual > 6 then FrameActual := 1; sleep(200); end; end; procedure TDrawHourGlass.ShowFrame1; begin (FfrmMessage as TfrmMessage).imgHourGlass.Picture.Bitmap.Assign((FfrmMessage as TfrmMessage).Frame1.Picture.Graphic); (FfrmMessage as TfrmMessage).imgHourGlass.Update; end; implementation procedure TDrawHourGlass.ShowFrame2; begin (FfrmMessage as TfrmMessage).imgHourGlass.Picture.Bitmap.Assign((FfrmMessage as TfrmMessage).Frame2.Picture.Graphic); (FfrmMessage as TfrmMessage).imgHourGlass.Update; end; procedure TDrawHourGlass.ShowFrame3; begin (FfrmMessage as TfrmMessage).imgHourGlass.Picture.Bitmap.Assign((FfrmMessage as TfrmMessage).Frame3.Picture.Graphic); (FfrmMessage as TfrmMessage).imgHourGlass.Update; end; procedure TDrawHourGlass.ShowFrame4; begin (FfrmMessage as TfrmMessage).imgHourGlass.Picture.Bitmap.Assign((FfrmMessage as TfrmMessage).Frame4.Picture.Graphic); (FfrmMessage as TfrmMessage).imgHourGlass.Update; end; procedure TDrawHourGlass.ShowFrame5; begin (FfrmMessage as TfrmMessage).imgHourGlass.Picture.Bitmap.Assign((FfrmMessage as TfrmMessage).Frame5.Picture.Graphic); (FfrmMessage as TfrmMessage).imgHourGlass.Update; end;

But I get the same result, while the main thread is busy the animation remains still, because the calls (FfrmMessage as TfrmMessage).imgHourGlass.Update; to draw each frame, waits until the main thread has finished (even when not calling them within a Synchronize).

Do you have a suggestion what can I also try ?.

Thank you.

Improve this question
9
  • Are you using FireDAC or another library? Commented Jul 19, 2017 at 14:18
  • Yes, FireDAC (calling a Datasnap remote method that returns a Dataset). Commented Jul 19, 2017 at 15:18
  • Well, then it's not a data component that needs to work in the background but a REST call (why would you need to display such dialog on server?). FireDAC has support for asynchronous mode, but for REST server it's unwanted. It has some threading model, as far as I remember. Commented Jul 19, 2017 at 15:34
  • 1
    I see. Then create a thread in which you'll be waiting for an execution event, do the REST call and post the received dataset as a parameter of a message posted to an invisible window created by AllocateHwnd, or use Synchronize to pass the dataset to the main thread. The animation keep running in the main thread. Create that form when the thread starts, destroy it when thread is terminated or starts waiting for another execution. Commented Jul 19, 2017 at 15:46
  • 1
    No, so long you keep the main thread message loop blocked by a long running synchronous call, any worker thread won't help you (Synchronize will execute after such call finishes). Rule of thumb for a responsible UI is, keep the main thread without any long running blocking calls (which such REST call is, so move that call to a worker thread). Commented Jul 19, 2017 at 16:36

2 Answers 2

Reset to default
4

It's very unfortunate that the many components in Delphi basically encourage poor application design (blocking the main thread). In situations like this, you should seriously consider swapping around the purpose of your thread, so that all lengthy processing is done inside of a thread (or multiple), and leave all the drawing up to the main UI thread. There aren't many clean ways to make the main thread responsive while it's processing any amount of data.

Improve this answer
Sign up to request clarification or add additional context in comments.

6 Comments

I would not say that data components do that. If you're speaking about binded data aware controls, then simply unbind them, do the work in the worker thread and bind them back. Or if the component supports asynchronous execution, you can give that a try.
@Victoria Indeed, certainly not all components, and not just a few either. Many of them, by nature, lock the main thread. And I don't mean anything with binding or data-aware components. Just executing a simple query on a table with millions of records is enough to lock the main thread - of course, depending on which components are being used.
I've never met what you say. If you execute query in a worker thread, it doesn't block the main one in general. We need more information about used technology to be more specific.
@Victoria Exactly, that's why I'm recommending it as a solution. In the original question: "The problem is that the animated Gif remains still while the main thread is busy (loading the query)" I don't understand your comment. The solution is the same, even for other components which have nothing to do with a database.
It's a REST call that needs to work in the background (see the answer to my question comment). Besides, FireDAC offers asynchronous execution modes, but not for this case. Here you are right in swapping the logic.
|
3

If it's only for a query and you're using FireDAC, then check out http://docwiki.embarcadero.com/RADStudio/Berlin/en/Asynchronous_Execution_(FireDAC) it seems to be possible.

To handle any kind of lengthy processing, you can use the Threading unit. You don't do the work in the main thread so the UI can be displayed correctly.

This example is not perfect (you should probably use some kind of callback), but the gif is spinning.

procedure TForm3.ButtonProcessClick(Sender: TObject); begin // Block UI to avoid executing the work twice ButtonProcess.Enabled := false; TTask.Create( procedure begin Sleep(10000); // Enable UI again ButtonProcess.Enabled := true; end).Start(); end;

To make the gif spin in the first place I use :

procedure TForm3.FormCreate(Sender: TObject); begin (GifLoading.Picture.Graphic as TGIFImage).Animate := true; end;

I haven't tried, but this link seems to provide something very close from what you want.

Hope this helps.

Improve this answer

4 Comments

Why would you use asynchronous execution on REST server? It's the REST client call that needs to run (and display that dialog) in background.
@Victoria I can think of plenty reasons. One of my own projects is an emulator for a credit card machine, which has a REST server inside of it, receiving commands.
@Victoria I haven't seen OP mentioning REST. The TForm3 class of my example suggests we're in a classic VCL heavy client application.
I see. Here is this comment.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.