Does VCL components have onCreate event?-CodePudding

Need to access some components right after program start but I have found that doing so from form's onCreate event is bad because at the moment they may still be unavailable (access violation occurs). Can not find onCreate event in any component. Am I missing something?

CodePudding user response：

Use the form's onShow() -event.

But be aware, that the onShow() -event is called every time the form is shown, not only the first time.

CodePudding user response：

In your form, you should override the DoShow method and insert your code there. Since DoShow is called everytime the form changes from invisible to visible, you should also add a boolean variable in your form and check in the DoShow override, if it is false. In that case, it is the first time DoShow is called. Then set the variable to true and do whatever you need to do the first time.

Please note that within DoShow the form is not visible yet. If you need to do something once the form is made visible, you can post a custom message from DoShow and put your code in the corresponding message handler. At the time it is executed, the form just became visible.

const
    WM_APP_STARTUP         = WM_USER   1;
type
    TForm1 = class(TForm)
    protected
        FInitialized            : Boolean;
        procedure DoShow; override;
        procedure WMAppStartup(var Msg: TMessage); message WM_APP_STARTUP;
    end;

implementation    
    procedure TForm1.DoShow;
    begin
        // Form is NOT visible but will soon be
        if not FInitialized then begin
            FInitialized := TRUE;
            // Insert your code here
            PostMessage(Handle, WM_APP_STARTUP, 0, 0);
        end;
        inherited DoShow;
    end;
    
    procedure TForm1.WMAppStartup(var Msg: TMessage);
    begin
        // The form is now visible
        // Insert your code here
    end;