Lobby and matchmaking basics in Unity - Step-by-Step Execution

Concept Flow - Lobby and matchmaking basics

Player opens game

↓

Connect to server

↓

Create or join lobby

↓

Wait for players

↓

Matchmaking starts

↓

Players matched

↓

Start game session

This flow shows how a player connects, joins or creates a lobby, waits for others, and then matchmaking pairs players to start a game.

Execution Sample

Unity

void Start()
{
    ConnectToServer();
    JoinOrCreateLobby();
    StartMatchmaking();
}

This code connects the player to the server, joins or creates a lobby, then starts matchmaking.

Execution Table

Step	Action	Condition/Check	Result/State Change	Output/Next Step
1	Call ConnectToServer()	Is server reachable?	Connected to server	Proceed to lobby
2	Call JoinOrCreateLobby()	Is lobby available?	Joined existing lobby	Wait for players
3	Wait for players	Enough players joined?	Players ready	Start matchmaking
4	Call StartMatchmaking()	Match found?	Players matched	Start game session
5	Start game session	Game ready?	Game started	Gameplay begins

💡 Game session started, matchmaking and lobby process complete

Variable Tracker

Variable	Start	After ConnectToServer	After JoinOrCreateLobby	After Wait for players	After StartMatchmaking	Final
isConnected	false	true	true	true	true	true
lobbyStatus	none	none	joined	joined	joined	joined
playersReady	0	0	0	enough	enough	enough
matchFound	false	false	false	false	true	true
gameStarted	false	false	false	false	false	true

Key Moments - 3 Insights

Why do we check if the server is reachable before joining a lobby?

Because joining a lobby requires a connection to the server. As shown in step 1 of the execution_table, if the server is not reachable, we cannot proceed to join or create a lobby.

What happens if there are not enough players in the lobby?

The matchmaking does not start until enough players join. Step 3 shows waiting for players; matchmaking only starts when playersReady is 'enough'.

Can the game start before matchmaking finds a match?

No, the game starts only after matchmaking finds a match, as shown in step 4 and 5 where matchFound must be true before gameStarted becomes true.

Visual Quiz - 3 Questions

Look at the variable_tracker table, what is the value of 'lobbyStatus' after JoinOrCreateLobby?

A none

B connected

C joined

D waiting

💡 Hint

Check the 'lobbyStatus' row under 'After JoinOrCreateLobby' column in variable_tracker.

At which step in the execution_table does matchmaking start?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look for the action 'Start matchmaking' in execution_table.

If the server is not reachable, what happens to 'isConnected' variable?

A It stays false

B It becomes null

C It becomes true

D It becomes 'connected'

💡 Hint

Refer to 'isConnected' in variable_tracker after 'ConnectToServer' step.

Concept Snapshot

Lobby and matchmaking basics in Unity:
- Connect to server first
- Join or create a lobby
- Wait for enough players
- Start matchmaking to find matches
- Begin game session after match
Use server connection and lobby status variables to track progress.

Full Transcript

This visual execution shows the basic steps of lobby and matchmaking in Unity. First, the player connects to the server. Then they join or create a lobby. The system waits until enough players join the lobby. After that, matchmaking starts to find suitable players to play together. Once a match is found, the game session starts and gameplay begins. Variables like isConnected, lobbyStatus, playersReady, matchFound, and gameStarted track the state at each step. Key moments include ensuring server connection before lobby join, waiting for enough players before matchmaking, and starting the game only after a match is found.

Practice

1. What is the main purpose of a lobby in Unity multiplayer games?

easy

A. To let players wait and prepare before the game starts

B. To automatically find and connect players

C. To render 3D graphics for the game

D. To save player progress locally

Solution

1. Step 1: Understand the role of a lobby

   A lobby is a waiting area where players gather before the game begins.

2. Step 2: Differentiate from matchmaking

   Matchmaking is the process of finding and connecting players automatically, not the lobby itself.

3. Final Answer:

   To let players wait and prepare before the game starts -> Option A

4. Quick Check:

   Lobby = waiting area before game [OK]

Hint: Lobbies are for waiting; matchmaking is for finding players [OK]

Common Mistakes:

• Confusing lobby with matchmaking
• Thinking lobby handles graphics
• Assuming lobby saves progress

2. Which of the following is the correct way to override a lobby method in Unity C#?

easy

A. public override void OnPlayerJoined() {}

B. override public void OnPlayerJoined() {}

C. public void OnPlayerJoined() override {}

D. void override OnPlayerJoined() {}

Solution

1. Step 1: Recall C# override syntax

   In C#, the correct syntax places 'override' before the return type.

2. Step 2: Check each option

   public override void OnPlayerJoined() {} uses 'public override void MethodName()' which is correct syntax.

3. Final Answer:

   public override void OnPlayerJoined() {} -> Option A

4. Quick Check:

   Override keyword before return type [OK]

Hint: In C#, 'override' comes before the return type [OK]

Common Mistakes:

• Placing override after method name
• Omitting override keyword
• Wrong order of keywords

3. Given this code snippet in a Unity lobby script:

public override void OnPlayerJoined(Player player) {
    Debug.Log($"Player {player.Name} joined.");
    if (Players.Count >= 4) {
        StartGame();
    }
}

What happens when the 4th player joins?

medium

A. The lobby closes without starting the game

B. Nothing happens until manually started

C. The game starts automatically

D. An error occurs because Players.Count is undefined

Solution

1. Step 1: Analyze the OnPlayerJoined method

   When a player joins, it logs their name and checks if Players.Count is 4 or more.

2. Step 2: Understand the condition

   If Players.Count is 4 or more, StartGame() is called, starting the game automatically.

3. Final Answer:

   The game starts automatically -> Option C

4. Quick Check:

   Players.Count >= 4 triggers StartGame() [OK]

Hint: Check conditions that trigger StartGame() call [OK]

Common Mistakes:

• Assuming manual start needed
• Thinking Players.Count is undefined
• Confusing lobby closing with game start

4. Identify the error in this matchmaking code snippet:

public void Matchmake() {
    var match = Matchmaker.CreateMatch();
    match.OnPlayerJoined += OnPlayerJoined;
    match.Start();
}

void OnPlayerJoined(Player player) {
    Debug.Log("Player joined: " + player.Name);
}

medium

A. Start() method does not exist on match object

B. Event subscription syntax is incorrect

C. OnPlayerJoined method must be public to subscribe

D. Matchmaker.CreateMatch() might return null and is not checked

Solution

1. Step 1: Review event subscription

   The syntax 'match.OnPlayerJoined += OnPlayerJoined;' is correct for subscribing to events.

2. Step 2: Check for null safety

   Matchmaker.CreateMatch() might return null if no match is found, but code does not check for null before using match.

3. Final Answer:

   Matchmaker.CreateMatch() might return null and is not checked -> Option D

4. Quick Check:

   Always check for null after CreateMatch() [OK]

Hint: Always check if CreateMatch() returns null before use [OK]

Common Mistakes:

• Assuming event subscription syntax is wrong
• Ignoring null checks
• Assuming Start() method is missing

5. You want to create a lobby that only starts the game when all players are ready. Which approach is best in Unity matchmaking?

hard

A. Call StartGame() immediately when the first player joins

B. Override OnPlayerJoined to check a 'ready' flag on each player before calling StartGame()

C. Use a timer to start the game after 30 seconds regardless of players

D. Disable matchmaking and start game manually from UI

Solution

1. Step 1: Understand the requirement

   The game should start only when all players are ready, not just when they join.

2. Step 2: Choose the best method

   Overriding OnPlayerJoined to check each player's 'ready' status before starting the game ensures all are prepared.

3. Final Answer:

   Override OnPlayerJoined to check a 'ready' flag on each player before calling StartGame() -> Option B

4. Quick Check:

   Check readiness before starting game [OK]

Hint: Check all players' ready flags before starting game [OK]

Common Mistakes:

• Starting game too early
• Ignoring player readiness
• Disabling matchmaking unnecessarily