Remote procedure calls in Unity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Unity RPC call?

Consider the following Unity C# code snippet using [ClientRpc]. What will be printed in the console when the server calls RpcShowMessage()?

Unity

using Unity.Netcode;
using UnityEngine;

public class MessageHandler : NetworkBehaviour
{
    [ClientRpc]
    public void RpcShowMessage()
    {
        Debug.Log("Hello from server to clients!");
    }

    public override void OnNetworkSpawn()
    {
        if (IsServer)
        {
            RpcShowMessage();
        }
    }
}

A All clients and the server print: Hello from server to clients!

B Only the server console prints: Hello from server to clients!

C No output is printed because RpcShowMessage is not called on clients.

D Only clients print: Hello from server to clients!, server does not print.

💡 Hint

Remember that [ClientRpc] methods run on clients when called by the server.

The RpcShowMessage() method is marked with [ClientRpc], so when the server calls it, the method runs on all clients and the server (if it is also a client). Therefore, all consoles print the message.

❓ Predict Output

intermediate

What happens when a client calls a ServerRpc without permission?

Given this Unity C# code snippet, what will happen if a client calls CmdChangeScore(10)?

Unity

using Unity.Netcode;
using UnityEngine;

public class ScoreManager : NetworkBehaviour
{
    private int score = 0;

    [ServerRpc]
    public void CmdChangeScore(int amount)
    {
        score += amount;
        Debug.Log($"Score changed to {score}");
    }
}

A The method runs on the client instead of the server, so score is not updated.

B The server updates the score and prints the new value.

C The server throws a security exception and disconnects the client.

D Nothing happens because clients cannot call ServerRpc methods.

💡 Hint

Clients can call [ServerRpc] methods to request actions on the server.

Clients are allowed to call [ServerRpc] methods. When a client calls CmdChangeScore(10), the server runs the method, updates the score, and prints the new value.

🔧 Debug

advanced

Why does this ServerRpc not execute on the server?

Examine the following code. The CmdSendData method is never executed on the server when called by a client. What is the cause?

Unity

using Unity.Netcode;
using UnityEngine;

public class DataSender : NetworkBehaviour
{
    [ServerRpc]
    public void CmdSendData(string data)
    {
        Debug.Log($"Data received: {data}");
    }

    void Update()
    {
        if (IsClient && Input.GetKeyDown(KeyCode.Space))
        {
            CmdSendData("Hello Server");
        }
    }
}

A The method name must start with 'Rpc' to be recognized as a ServerRpc.

B The client is not connected to the server, so the ServerRpc never reaches the server.

C The method is missing the <code>RequireOwnership = false</code> attribute, so the client must own the object to call the ServerRpc.

D The method is private and cannot be called from clients.

💡 Hint

Check ownership requirements for ServerRpc calls.

By default, ServerRpc methods require the client to own the NetworkObject to call them. If the client does not own it, the ServerRpc is ignored. Adding [ServerRpc(RequireOwnership = false)] allows any client to call it.

📝 Syntax

advanced

Identify the syntax error in this ClientRpc method

Which option correctly fixes the syntax error in this ClientRpc method?

Unity

using Unity.Netcode;
using UnityEngine;

public class Notifier : NetworkBehaviour
{
    [ClientRpc]
    public void RpcNotify(string message)
    {
        Debug.Log(message)
    }
}

A Change the method to static void RpcNotify(string message)

B Change Debug.Log(message) to Debug.Log(message); return;

C Remove the parentheses from Debug.Log to Debug.Log;

D Add a semicolon after Debug.Log(message);

💡 Hint

Check for missing punctuation in C# statements.

The line Debug.Log(message) is missing a semicolon at the end. Adding it fixes the syntax error.

🚀 Application

expert

How to synchronize a player's health using RPCs?

You want to keep all clients updated with the player's health value in a multiplayer Unity game using Netcode. Which approach using RPCs is best?

A Use a <code>[ServerRpc]</code> method for clients to send health changes to the server, then a <code>[ClientRpc]</code> method to broadcast the updated health to all clients.

B Use only a <code>[ClientRpc]</code> method to send health updates from clients to the server.

C Use only a <code>[ServerRpc]</code> method to send health updates from the server to clients.

D Use local variables on each client and do not use RPCs for health synchronization.

💡 Hint

Think about how data flows from clients to server and then to all clients.

Clients send health changes to the server using [ServerRpc]. The server then broadcasts the updated health to all clients using [ClientRpc]. This ensures consistent health state across all players.