CODEWITHSUNDEEP
delphi
user6695319
user6695319

Reputation:

How to use the Initialization and Finalization command in Delphi?

When I generate new application project on Delphi, the first Line of Implementation in source Project1.pas is the following.

Application.Initialize; 
Application.CreateForm(Tform1, form1);
Application.Run;

Then in event OnCreate of Form1 I realize all initialization I need, like Open FdConnections, Activate Queries and so on. I am also closing all Queries and Connection in OnClose of form. Would be Initialization and Finalization one good alternative to do do that? What's this commands purpose, and what different of OnCreate?

var Form1:TForm1;
Implementation

Initialization
Begin
FdConnection1.Open;
FdQuery1.open;
FdQuery2.Open;
...
End;
Finalization
Begin
FdQuery1.Close
...
FdConnection.Close;
End; {Could It works?}

Upvotes: 1

Views: 7894

Answers (2)

MartynA
MartynA

Reputation: 30735

To follow the order of events when a Delphi application starts up, try the following:

  1. Create an Initialization section in your Form1's unit, put some inconsequential code in it and set a debug breakpoint on it. The point of this code is simply so that you can put a breakpoint on it.

  2. Create a Finalization section in your Form1's unit, put some code in that and put a breakpoint on it.

  3. Put a break point on Application.Initialize in your .Dpr file.

  4. Compile and run the app.

  5. The debugger will stop on the breakpoint you created in step 1. If you view the call stack, you will see that the code is being called as a result of being called from the RTL routine InitUnits which calls in turn the initialization section of each unit compiled into your .Exe. The exact order they are called is determined by the compiler at compile time and presumably determined by a depth-first traversal of the USEd units.

  6. Next, the debugger will stop on the Application.Initialize BP in the .Dpr file. By the time execution reaches there, the Initialization sections of all the units compiled into the .Exe will have been called.

  7. When you close the application, the debugger will stop on the Finalization BP you set in step 2. If you trace out of it, you will find that it calls the Finalization sections of the units in the reverse order to the order the Initialization sections were called. And these Initialization and Finalization sections are called only once per execution of the .Exe.

It ought to be apparent from the above that the calls to the Initialization/Finalization sections are unrelated to whether any classes in the units are ever instantiated. The prime reason to instantiate a class in an Initialization section is to ensure that the class instance exists before Application.Initialize is called (or the equivalent of Main() is called in a console application).

Upvotes: 4

bitshftr
bitshftr

Reputation: 54

The Initialization and Finalization sections execute exactly once, no matter how many instances of a Form are created. Contrast that with the OnCreate, OnClose, and OnDestroy events of a Form, which execute once for each instance.

In your example, the Form in question is only created once, so the difference really applies more to Forms that are (or can be) created (instantiated) multiple times, whether each instance is closed or not.

Upvotes: 2

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