C# Design Pattern: Flyweight

The Flyweight pattern is useful for saving memory by sharing heavy objects that can be used by multiple instances. In this example, we deal with file icons. Each file type (PDF, Word, Image) has its own icon, but many files share the same icon. By using Flyweight, we can load the icon once and reuse it for all files of the same type, instead of loading the image repeatedly.

C# Code Example:

// Flyweight: File Icon
public class FileIcon
{
    private string _iconName;

    public FileIcon(string iconName)
    {
        _iconName = iconName;
        Console.WriteLine($"Loading icon {_iconName} from memory...");
    }

    public void Display(int size)
    {
        Console.WriteLine($"Displaying icon {_iconName} with size {size}.");
    }
}

// Flyweight Factory: File icon manager
public class IconFactory
{
    private Dictionary<string, FileIcon> _icons = new Dictionary<string, FileIcon>();

    public FileIcon GetIcon(string fileType)
    {
        if (!_icons.ContainsKey(fileType))
        {
            _icons[fileType] = new FileIcon(fileType);
        }
        return _icons[fileType];
    }
}

// Class representing an individual file
public class File
{
    private string _name;
    private FileIcon _icon;

    public File(string name, FileIcon icon)
    {
        _name = name;
        _icon = icon;
    }

    public void Display()
    {
        Console.WriteLine($"Displaying file: {_name}");
        _icon.Display(32);
    }
}

class Program
{
    static void Main(string[] args)
    {
        IconFactory factory = new IconFactory();

        // Load and share icons for different file types
        FileIcon pdfIcon = factory.GetIcon("PDF");
        FileIcon wordIcon = factory.GetIcon("Word");
        FileIcon imageIcon = factory.GetIcon("Image");

        // Create files with shared icons
        File file1 = new File("Document1.pdf", pdfIcon);
        File file2 = new File("Document2.pdf", pdfIcon);
        File file3 = new File("Report.docx", wordIcon);
        File file4 = new File("Photo.jpg", imageIcon);

        // Display files with their icons
        file1.Display();  // Output: Displaying file: Document1.pdf. Displaying icon PDF with size 32.
        file2.Display();  // Output: Displaying file: Document2.pdf. Displaying icon PDF with size 32.
        file3.Display();  // Output: Displaying file: Report.docx. Displaying icon Word with size 32.
        file4.Display();  // Output: Displaying file: Photo.jpg. Displaying icon Image with size 32.
    }
}

Code Explanation:

In this example, the FileIcon class represents an icon shared between different files of the same type. The IconFactory manages these icons and ensures that each file type (PDF, Word, Image) has only one icon loaded in memory. When a file is created, it gets the appropriate icon from the factory, reusing the existing icon if it’s already loaded.

Conclusion:

The Flyweight pattern is useful in scenarios where you have many similar objects that can share common data, such as file icons. It helps save memory by avoiding the creation of multiple instances of the same icon, making the system more efficient.

Source code: GitHub