HelloWorld-quickstart_2.md

We discussed the most basic ideas about the delphivcl library in the first simplest quickstart. We created an empty GUI application without displaying anything on the Form/GUI window. Also, we didn't use any object-oriented approach to create the GUI application. So, let's expand on those ideas and develop an object-oriented version of that and display a text message.

First, let's look at the code to achieve our idea. You might be able to guess what the below code does as you understood the basics from the first guide.

from delphivcl import *

class GUIApp(Form):

    def __init__(self, owner):
        self.SetProps(Caption = "Welcome")

        self.lblHello = Label(self)
        self.lblHello.SetProps(
            Parent=self,
            Caption="Hello DelphiVCL for Python")

def main():
    Application.Initialize()
    Application.Title = "Hello Delphi VCL"
    app = GUIApp(Application)
    app.Show()
    FreeConsole()
    Application.Run()
    app.Destroy()

main()

As you save the above code in a Python file and run it, you'll get the following GUI window with a text message as follows:

In the following line of the code;

    app = GUIApp(Application)

Instead of instantiating the Form directly, we instantiated a class - GUIApp that inherited the Form class. Let's investigate the code in the GUIApp class:

class GUIApp(Form):

    def __init__(self, owner):
        self.SetProps(Caption = "Welcome")

        self.lblHello = Label(self)
        self.lblHello.SetProps(
            Parent=self,
            Caption="Hello DelphiVCL for Python")

As we instantiated the GUIApp using app = GUIApp(Application), the owner argument gets assigned with the Application object. After that, Form uses the owner in its initialization and creates an empty Form/GUI window. This owner variable can be of any other name as it's just a placeholder of the Application object. In the first line of the GUIApp initialization, we've set the Caption property of the Form.

Then we instantiated the Label component/class with the instance/object of the Form as its parameter using the self.lblHello = Label(self) code snippet. We use Label to display any single-line text messages. Every component other than Form will have a parent and is set using the Parent property. The parent holds the child component in it.

In our code, we're setting Label's parent as Form using the Parent=self. So, now the Form object - app holds the Label object - lblHello. Next, the text of the Label is set using its Caption property. So, the Form/GUI window gets populated by a text message - Hello DelphiVCL for Python.

We used all the default positions and sizes of the Form and Label and didn't handle any events in this guide. However, we shall implement them and introduce some new components in the following advanced quick start guide.