What is called after Loaded() in Delphi

Question

I have some code that does some setup of internal objects in the Loaded() function. However, some external objects are not completely created yet, but are AFTER the Loaded() function is complete. What function does Delphi call after it calls Loaded()?

Better yet what is the creation sequence of a component?

Basically I have a TCP Server and Client. Most people will place those two components into two separate applications, some will place them in the same application for local access.

My Client tries to fetch data from the server in OnLoaded(), but the server may not be up yet! I want to know if another function is called after all the OnLoaded()'s are called.

Answer 1

Normally you would override TObject.AfterConstruction for that purpose.

The order of execution is:

  each Component.AfterConstruction in creation order
(Form or DataModule).Loaded  
  each Component.Loaded in creation order
(Form or DataModule).AfterConstruction 

Trace:

Debug Output: button AfterConstruction Process Project2.exe (4876)
Debug Output: Form Loaded Process Project2.exe (4876)
Debug Output: button Loaded Process Project2.exe (4876)
Debug Output: Form AfterConstruction Process Project2.exe (4876)

Answer 2

I'm not sure what you mean with

the server may not be up yet

Anyway, if the client and the server are both on the same application form or datamodule, I see alternatives:

1. You may "force" the system to create the server before the client and up the server in the server's OnLoad and it will be up at the client OnLoad, because documentation says:

   When the streaming system loads a form or data module from its form file, it first constructs the form component by calling its constructor, then reads its property values from the form file. After reading all the property values for all the components, the streaming system calls the Loaded methods of each component in the order the components were created. This gives the components a chance to initialize any data that depends on the values of other components or other parts of itself.

2. Inform the "client" whenever the server is UP to let it initialize (pull data from the server). You can use a direct method call, post a message or whatever you feel comfortable with.

3. Let the client stand up the server inside it's own OnLoad method.

Answer 3

Why not use the onCreate event of the main Form ?

Answer 4

Loaded is called immediately after the dfm is streamed in, and shouldn't be used to access the server. Your best bet is probably to post a custom message to yourself in the constructor, and have a message handler procedure that responds to that message. Posting the message puts it into the end of the message queue, and therefore it won't get processed until all the other messages ahead of it has been handled. This should delay things long enough for your components to be fully constructed for use.