Bridge

• Acts as a bridge between 2 independent hierarchies
• Build flexible hierarchies that can grow independent of each other.

Classical Structure

Scenario

• Build a remote control app to control various brands of TV

Problem

public abstract class RemoteControl
{
    public abstract void TurnOn();
    public abstract void TurnOff();
}
public abstract class AdvancedRemoteControl : RemoteControl
{
    public abstract void SetChannel(int number);
}
public class SonyRemoteControl : RemoteControl
{
    public override void TurnOff()
    {
        Console.WriteLine("Turn off");
    }

    public override void TurnOn()
    {
        Console.WriteLine("Turn on");
    }
}
public class SonyAdvancedRemoteControl : AdvancedRemoteControl
{
    public override void SetChannel(int number)
    {
        Console.WriteLine("Set channel");
    }

    public override void TurnOff()
    {
        Console.WriteLine("Turn off");
    }

    public override void TurnOn()
    {
        Console.WriteLine("Turn on");
    }
}

• Every time you want to support a new TV brand, you have to create concrete classes for that
• Also every time you introduce a new remote control (eg MovieRemoteControl), you have to provide concrete class for all brands
• Hierarchy gets more complex, every time you want to support a new TV brand or new remote control
• Hierarchy grows into 2 different dimensions (feature and implementation)

Solution

• Whenever hierarchy grows into 2 different dimensions, split into 2 separate hierarchies and connect them using bridge

public interface IDevice
{
    void TurnOn();
    void TurnOff();
    void SetChannel(int number);
}
public class SonyTV : IDevice
{
    public void SetChannel(int number)
    {
        Console.WriteLine("SonyTV Set Channel");
    }

    public void TurnOff()
    {
        Console.WriteLine("SonyTV Turn Off");
    }

    public void TurnOn()
    {
        Console.WriteLine("SonyTV Turn On");
    }
}
public class SamsungTV: IDevice
{
    public void SetChannel(int number)
    {
        Console.WriteLine("SamsungTV Set Channel");
    }

    public void TurnOff()
    {
        Console.WriteLine("SamsungTV Turn Off");
    }

    public void TurnOn()
    {
        Console.WriteLine("SamsungTV Turn On");
    }
}
public class RemoteControl
{
    protected IDevice device;

    public RemoteControl(IDevice device)
    {
        this.device = device;
    }

    public void TurnOn()
    {
        device.TurnOn();
    }
    public void TurnOff()
    {
        device.TurnOff();
    }
}
public class AdvancedRemoteControl : RemoteControl
{
    public AdvancedRemoteControl(IDevice device) : base(device)
    {
    }

    public void SetChannel(int number)
    {
        device.SetChannel(number);
    }
}
public class Program
{
    static void Main(string[] args)
    {
        var remoteControl = new AdvancedRemoteControl(new SamsungTV());
        remoteControl.TurnOn();
    }
}

Example Structure

Example Code