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Reconnecting to a session

You can permit players to reconnect to a session they were in after their connection gets disrupted by using the FindFriendSession function. This is often used to allow players to rejoin a game after their Internet drops or their game client crashes.

Note that the game server must not have unregistered them as a player in order for this technique to work. Refer to Unregister players for more detail on the requirements to support reconnections.

Checking if a session is available to reconnect to​

You will most likely want to perform this check at the main menu of your game, and at the menu that a user is sent back to after a disconnection, so that you can offer them the option of reconnecting to the game.

First, get the online session interface:

#include "OnlineSubsystem.h"
#include "OnlineSubsystemUtils.h"
#include "Interfaces/OnlineSessionInterface.h"

// ...

IOnlineSubsystem* Subsystem = Online::GetSubsystem(this->GetWorld());
IOnlineSessionPtr Session = Subsystem->GetSessionInterface();

Register the event handler so you know when you receive the search results. FindFriendSessionDelegateHandle is declared as an FDelegateHandle.

this->FindFriendSessionDelegateHandle =
    Session->AddOnFindFriendSessionCompleteDelegate_Handle(
        0 /* LocalUserNum */, 
        FOnFindFriendSessionComplete::FDelegate::CreateUObject(
            this,
            &UMyClass::HandleFindFriendSessionComplete));

Call FindFriendSession, using the current user ID as the "friend ID" parameter:

if (!Session->FindFriendSession(0 /* LocalUserNum */, *UserId))
{
    // Call didn't start, return error.
    Session->ClearOnFindFriendSessionCompleteDelegate_Handle(0 /* LocalUserNum */, this->FindFriendSessionDelegateHandle);
}

When your callback fires, you can handle whether or not a session is available:

void UMyClass::HandleFindFriendSessionComplete(
    int32 LocalUserNum,
    bool bWasSuccessful,
    const TArray<FOnlineSessionSearchResult> &Results)
{
    // NOTE: bWasSuccessful is only true if the call succeeded *AND* a session was found.
    // It's normal for it to be false when the call succeeds if the user doesn't have
    // a session to reconnect to. You should not treat a false value as an indication to
    // retry the request.

    if (bWasSuccessful && Results.Num() > 0)
    {
        // The user has a session they can reconnect to. You can handle the (at most one)
        // search result from the Results array the same way that search results
        // are handled in "Finding a session".

        Session->ClearOnFindFriendSessionCompleteDelegate_Handle(this->FindFriendSessionDelegateHandle);
        this->FindFriendSessionDelegateHandle.Reset();
        return;
    }

    // Otherwise, the user does not have a session to reconnect to.
    Session->ClearOnFindFriendSessionCompleteDelegate_Handle(this->FindFriendSessionDelegateHandle);
    this->FindFriendSessionDelegateHandle.Reset();
}

Refer to Connecting to a game server on how to use the search result to reconnect to the game server.