Your team is developing VisageTome, a social media platform to rival the greates
ID: 3920149 • Letter: Y
Question
Your team is developing VisageTome, a social media platform to rival the greatest systems of the day. The project is off to a good start, but your manager now wants you to add notifications to the system; specifically, she wants users to be able to follow one another and receive a message when the followed user's status changes. Add an event to the User class and use it to wire up these notifications.
The system begins by executing a list of commands from a document before allowing the user to input commands.
VisageTome.cs
using System;
using System.IO;
using System.Collections.Generic;
class VisageTome
{
#region Main
private static Dictionary<string, User> users = new Dictionary<string, User>();
static void Main()
{
Console.WriteLine("Welcome to VisageTome!");
Console.WriteLine("Executing from file...");
foreach(string line in File.ReadAllLines("commands.txt"))
{
Console.WriteLine(" > {0}", line);
ProcessCommand(line);
}
Console.WriteLine(" Executing from user...");
bool continue_user_input = true;
while(continue_user_input)
{
Console.Write(" > ");
string command = Console.ReadLine();
continue_user_input = ProcessCommand(command);
}
}
static bool ProcessCommand(string command)
{
string[] command_split = command.Split(' ');
if(command_split.Length >= 1)
{
if(command_split[0] == "user")
{
if(command_split.Length >= 2)
{
string new_user = command_split[1];
if(users.ContainsKey(new_user))
{
Console.WriteLine("User {0} already exists.", new_user);
}
else
{
users.Add(new_user, new User(new_user));
Console.WriteLine("User {0} added.", new_user);
}
}
else
{
Console.WriteLine("Usage: user <username>");
}
}
else if(command_split[0] == "list")
{
Console.WriteLine("Users:");
foreach(User user in users.Values)
{
Console.WriteLine(" {0}: {1}", user.Name, user.Status);
}
}
else if(command_split[0] == "status")
{
if(command_split.Length >= 3)
{
string user = command_split[1];
if(users.ContainsKey(user))
{
string status = command.Replace("status "+user+" ", "");
Console.WriteLine("User {0} status changing to "{1}".", user, status);
users[user].Status = status;
}
else
{
Console.WriteLine("User {0} does not exist.", user);
}
}
else
{
Console.WriteLine("Usage: status <username> <new status>");
}
}
else if(command_split[0] == "follow")
{
if(command_split.Length >= 3)
{
string follower = command_split[1];
string target = command_split[2];
if(users.ContainsKey(follower) && users.ContainsKey(target))
{
users[follower].FollowUser(users[target]);
Console.WriteLine("User {0} now following user {1}.", follower, target);
}
else
{
Console.WriteLine("User {0} and/or user {1} not found.", follower, target);
}
}
else
{
Console.WriteLine("Usage: follow <follower> <target>");
}
}
else if(command_split[0] == "unfollow")
{
if(command_split.Length >= 3)
{
string follower = command_split[1];
string target = command_split[2];
if(users.ContainsKey(follower) && users.ContainsKey(target))
{
users[follower].UnfollowUser(users[target]);
Console.WriteLine("User {0} no longer following user {1}.", follower, target);
}
else
{
Console.WriteLine("User {0} and/or user {1} not found.", follower, target);
}
}
else
{
Console.WriteLine("Usage: unfollow <follower> <target>");
}
}
else if(command_split[0] == "quit")
{
return false;
}
else
{
Console.WriteLine("Usage: <command> [command_args]");
Console.WriteLine("Valid commands: user list status follow unfollow quit");
}
}
else
{
Console.WriteLine("Usage: <command> [command_args]");
Console.WriteLine("Valid commands: user status follow unfollow quit");
}
return true;
}
#endregion
#region User Class
class User
{
private string name;
public string Name { get { return name;} }
private string status;
public string Status
{
get { return status; }
set
{
if(value != status)
{
status = value;
//TODO: Invoke an event that notifies subscribers that this user's status has changed
}
}
}
//TODO: Declare an EventHandler delegate to handle subscribers
public User(string name)
{
this.name = name;
status = "(No status yet)";
}
public void FollowUser(User other)
{
//TODO: Let this user subscribe to the status changed event of the other user;
// be sure to keep the subscriber from subscribing multiple times
}
public void UnfollowUser(User other)
{
//TODO: Let this user unsubscribe from the status changed event of the other user
}
private void ReceiveStatusChanged(object sender, StatusChangedEventArgs e)
{
//In a full application, this might involve sending an email or a pop-up to this user
Console.WriteLine(" {0} has been notified that {1}'s status has just changed to "{2}".", Name, e.Name, e.NewStatus);
}
//TODO: Properly finish the StatusChangedEventArgs class (see ReceiveStatusChanged for a use example)
public class StatusChangedEventArgs : EventArgs
{
}
}
#endregion
}
Explanation / Answer
Hi Programmer,
I have completed the program as mentioned. I have used custom event accessors to prevent user from over subscribing. I have ran the program and it runs fine. You can directly copy the code to a program in visual studio and run.
If my answer satisfies all your requirements please upvote it. Thanks in advance.
Below is the entire program,
using System;
using System.IO;
using System.Collections.Generic;
namespace Chegg_StatusNotification
{
class VisageTome
{
#region Main
private static Dictionary<string, User> users = new Dictionary<string, User>();
static void Main()
{
Console.WriteLine("Welcome to VisageTome!");
Console.WriteLine("Executing from file...");
foreach (string line in File.ReadAllLines("commands.txt"))
{
Console.WriteLine(" > {0}", line);
ProcessCommand(line);
}
Console.WriteLine(" Executing from user...");
bool continue_user_input = true;
while (continue_user_input)
{
Console.Write(" > ");
string command = Console.ReadLine();
continue_user_input = ProcessCommand(command);
}
}
static bool ProcessCommand(string command)
{
string[] command_split = command.Split(' ');
if (command_split.Length >= 1)
{
if (command_split[0] == "user")
{
if (command_split.Length >= 2)
{
string new_user = command_split[1];
if (users.ContainsKey(new_user))
{
Console.WriteLine("User {0} already exists.", new_user);
}
else
{
users.Add(new_user, new User(new_user));
Console.WriteLine("User {0} added.", new_user);
}
}
else
{
Console.WriteLine("Usage: user <username>");
}
}
else if (command_split[0] == "list")
{
Console.WriteLine("Users:");
foreach (User user in users.Values)
{
Console.WriteLine(" {0}: {1}", user.Name, user.Status);
}
}
else if (command_split[0] == "status")
{
if (command_split.Length >= 3)
{
string user = command_split[1];
if (users.ContainsKey(user))
{
string status = command.Replace("status " + user + " ", "");
Console.WriteLine("User {0} status changing to "{1}".", user, status);
users[user].Status = status;
}
else
{
Console.WriteLine("User {0} does not exist.", user);
}
}
else
{
Console.WriteLine("Usage: status <username> <new status>");
}
}
else if (command_split[0] == "follow")
{
if (command_split.Length >= 3)
{
string follower = command_split[1];
string target = command_split[2];
if (users.ContainsKey(follower) && users.ContainsKey(target))
{
users[follower].FollowUser(users[target]);
Console.WriteLine("User {0} now following user {1}.", follower, target);
}
else
{
Console.WriteLine("User {0} and/or user {1} not found.", follower, target);
}
}
else
{
Console.WriteLine("Usage: follow <follower> <target>");
}
}
else if (command_split[0] == "unfollow")
{
if (command_split.Length >= 3)
{
string follower = command_split[1];
string target = command_split[2];
if (users.ContainsKey(follower) && users.ContainsKey(target))
{
users[follower].UnfollowUser(users[target]);
Console.WriteLine("User {0} no longer following user {1}.", follower, target);
}
else
{
Console.WriteLine("User {0} and/or user {1} not found.", follower, target);
}
}
else
{
Console.WriteLine("Usage: unfollow <follower> <target>");
}
}
else if (command_split[0] == "quit")
{
return false;
}
else
{
Console.WriteLine("Usage: <command> [command_args]");
Console.WriteLine("Valid commands: user list status follow unfollow quit");
}
}
else
{
Console.WriteLine("Usage: <command> [command_args]");
Console.WriteLine("Valid commands: user status follow unfollow quit");
}
return true;
}
#endregion
#region User Class
class User
{
private string name;
public string Name { get { return name; } }
private string status;
//TODO: Declare an EventHandler delegate to handle subscribers
private EventHandler<StatusChangedEventArgs> statusChanged;
public event EventHandler<StatusChangedEventArgs> StatusChanged
{
add
{
if (statusChanged == null || !DoesEventSubscriberExist(value))
{
statusChanged += value;
}
}
remove { statusChanged -= value; }
}
private bool DoesEventSubscriberExist(EventHandler<StatusChangedEventArgs> Subscriber)
{
bool exists = false;
foreach(var subscription in statusChanged.GetInvocationList())
{
if (subscription.Equals(Subscriber))
{
exists = true;
break;
}
}
return exists;
}
public string Status
{
get { return status; }
set
{
if (value != status)
{
status = value;
//TODO: Invoke an event that notifies subscribers that this user's status has changed
if (statusChanged != null)
{
statusChanged(this, new StatusChangedEventArgs(name, status));
}
}
}
}
public User(string name)
{
this.name = name;
status = "(No status yet)";
}
public void FollowUser(User other)
{
//TODO: Let this user subscribe to the status changed event of the other user;
other.StatusChanged += ReceiveStatusChanged;
// be sure to keep the subscriber from subscribing multiple times
}
public void UnfollowUser(User other)
{
//TODO: Let this user unsubscribe from the status changed event of the other user
other.StatusChanged -= ReceiveStatusChanged;
}
private void ReceiveStatusChanged(object sender, StatusChangedEventArgs e)
{
//In a full application, this might involve sending an email or a pop-up to this user
Console.WriteLine(" {0} has been notified that {1}'s status has just changed to "{2}".", Name, e.Name, e.NewStatus);
}
//TODO: Properly finish the StatusChangedEventArgs class (see ReceiveStatusChanged for a use example)
public class StatusChangedEventArgs : EventArgs
{
public readonly string Name;
public readonly string NewStatus;
public StatusChangedEventArgs(string name, string newStatus)
{
Name = name; NewStatus = newStatus;
}
}
}
#endregion
}
}
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