Description
Provide a surrogate or placeholder for another object to control access to it.
- Control access to an object
- Proxy and subject objects share the same interface
Proxy vs decorator pattern
- Decorator informs and empowers its client, it adds functionalities to an object.
The client knows those functionalities.
- Proxy restricts and disempowers its client, it controls access to an object.
The client doesn't know those control access functionalities.
Exemple
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public class User
{
public string Name { get; set; }
}
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| IUserClient.cs
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public interface IUserClient
{
IReadOnlyList<User> GetUsers();
}
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| UserClient.cs
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public class UserClient : IUserClient
{
public IReadOnlyList<User> GetUsers()
{
return new[]
{
new User { Name = "Nicolas" },
new User { Name = "Paul" }
};
}
}
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| ProxyUserClient
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public class ProxyUserClient : IUserClient
{
private UserClient userClient;
public bool Authenticate(string userName, string password)
{
if (userName == "Nicolas" && password == "0000")
{
userClient = new UserClient();
return true;
}
return false;
}
public IReadOnlyList<User> GetUsers() => userClient?.GetUsers();
}
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|
IUserClient userClient = new UserClient();
// call GetUsers from UserClient: no restrictions
var users = userClient.GetUsers();
Console.WriteLine(string.Join('\n', users.Select(x => $"{x.Name}")));
userClient = new ProxyUserClient();
// authentication
((ProxyUserClient)userClient).Authenticate("Nicolas", "0000");
// call GetUsers from ProxyUserClient: authentication restriction
users = userClient.GetUsers();
if (users == null)
Console.WriteLine("You need to authenticate first.");
else
Console.WriteLine(string.Join('\n', users.Select(x => $"{x.Name}")));
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