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Keep Your Promises: The Liskov Substitution Principle Made Simple

If you're learning clean code, you'll keep running into the "SOLID" principles. The L stands for the Liskov Substitution Principle (LSP) — a scary name for a genuinely simple idea. This guide starts from zero, so no prior knowledge is needed. What it is The Liskov Substitution Principle says: If something is supposed to work like a certain type, then any "version" of that type must be able to take its place without causing problems. That's the whole thing. If you call something a Doctor , it has to actually behave like a doctor everywhere a doctor is expected. If you call something an ApiClient , it has to behave like one everywhere. Break that, and your program fails — usually later, in a confusing way. The principle is named after Barbara Liskov, a computer scientist who described it back in 1987. But you don't need the academic version to use it well. First, what does "substitute" mean? This is the word that makes the whole pr...
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ListView and ListTile!

Listview and Listtile are basic widgets, which are used to make a scrollable lists of item in a mobile app. They are essential component for building app where we need various type of lists, such as menus, chat message lists and etc.



ListView: Listview is a widget used to create a scrollable list of children. It can hold a list of widgets and automatically handles scrolling when the content exceeds the available space.

ListTile: Listtile widget is designed to represent a single item within a list. It typically contains title, subtitle, leading or trailing icon and can be made tappable.

Key Properties of listTile:

  • Title: The primary content of the list item.
  • Subtitle: Optional secondary content.
  • leading: A widget display before the title.
  • trailing: A widget display after the title.
  • Ontap: A callback function that is triggered when the listtile tapped.

Both Listview and Listtile are highly customizable, and you can style them according to the app design requirements. They are versatile and widely used in Flutter app development for presenting list of data or options to users in an organized and user-friendly manner.

body: Container(
  margin: const EdgeInsets.fromLTRB(0, 10, 8, 0),
  child: ListView(
    itemExtent: 70.0,
    children:  [
      ListTile(
        title: Text(
          "Top Faculties(UITS)",
          style: TextStyle(fontSize: 25, fontWeight: FontWeight.bold, color: Colors.red),
          textAlign: TextAlign.center,
        ),
      ),
      ListTile(
        leading: Container(
           height: double.infinity,
            child: Icon(Icons.computer)
        ),
        title: Text(
          "Computer Science",
          style: TextStyle(fontWeight: FontWeight.bold),
        ),
        subtitle: Text("We are the first it university......"),
        trailing: Text("300000"),
        onTap: () {},
      ),
      ListTile(
        leading: Container(
            height: double.infinity,
            child: Icon(Icons.medical_information)
        ),
        title: Text(
          "Pharmacy",
          style: TextStyle(fontWeight: FontWeight.bold),
        ),
        subtitle: Text("We have best medicine......"),
        trailing: Text("450000"),
        onTap: (){},
      ),
      ListTile(
        leading: Container(
          height: double.infinity,
          child: Icon(Icons.electric_bolt)
        ),
        title: Text(
          "Electrical Engineering",
          style: TextStyle(fontWeight: FontWeight.bold),
        ),
        subtitle: Text("Our students works at best....."),
        trailing: Text("500400"),
        onTap: (){},
      )
    ],
  ),
),

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Keep Your Promises: The Liskov Substitution Principle Made Simple

If you're learning clean code, you'll keep running into the "SOLID" principles. The L stands for the Liskov Substitution Principle (LSP) — a scary name for a genuinely simple idea. This guide starts from zero, so no prior knowledge is needed. What it is The Liskov Substitution Principle says: If something is supposed to work like a certain type, then any "version" of that type must be able to take its place without causing problems. That's the whole thing. If you call something a Doctor , it has to actually behave like a doctor everywhere a doctor is expected. If you call something an ApiClient , it has to behave like one everywhere. Break that, and your program fails — usually later, in a confusing way. The principle is named after Barbara Liskov, a computer scientist who described it back in 1987. But you don't need the academic version to use it well. First, what does "substitute" mean? This is the word that makes the whole pr...
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