How to do it...

1. Add #define to your main header file (ProjectName.h), defining LOCTEXT_NAMESPACE as something unique to your codebase:

#define LOCTEXT_NAMESPACE "Chapter11Namespace"

This #define is used by the LOCTEXT() macro, which we use to generate FText objects, but is not seen in output messages.

2. Declare your FMessageLog by constructing it somewhere very global. You can use extern in your ProjectName.h file. Consider the following piece of code as an example:

#define LOCTEXT_NAMESPACE "Chapter11Namespace"
#define FTEXT(x) LOCTEXT(x, x) 

extern FName LoggerName;

void CreateLog(FName logName);

3. Then, create your FMessageLog by defining it in a .cpp file and registering it with MessageLogModule. Be sure to give your logger a clear and unique name on construction. It's the category of your log that will appear to the left of your log messages in Output Log. For example, ProjectName.cpp:

#include "Chapter_11.h"
#include "Modules/ModuleManager.h"
#include "MessageLog/Public/MessageLogModule.h"
#include "MessageLog.h"

// ...

FName LoggerName("MessageLogChapter11");

void CreateLog(FName logName)
{
    FMessageLogModule& MessageLogModule = FModuleManager::LoadModuleChecked<FMessageLogModule>("MessageLog");
    FMessageLogInitializationOptions InitOptions;
    InitOptions.bShowPages = true;
    InitOptions.bShowFilters = true;
    FText LogListingName = FTEXT("Chapter 11's Log Listing");
    MessageLogModule.RegisterLogListing(logName, LogListingName, InitOptions);
}

4. Then, head back to somewhere in your code to actually create the log and use it. For example, we can add the following GameModeBase class's BeginPlay method:

void AChapter_11GameModeBase::BeginPlay()
{
    // 11-01 - Core/Logging API - Defining a custom log
    // category
    // Traditional Logging
    UE_LOG(LogTemp, Warning, TEXT("Message %d"), 1);

    // Our custom log type
    UE_LOG(LogCh11, Display, TEXT("A display message, log is working" ) ); // shows in gray 
    UE_LOG(LogCh11, Warning, TEXT("A warning message"));
    UE_LOG(LogCh11, Error, TEXT("An error message "));

    // 11-02 - Core/Logging API - FMessageLog to write 
    // messages to the Message Log
    CreateLog(LoggerName);
    // Retrieve the Log by using the LoggerName. 
    FMessageLog logger(LoggerName);
    logger.Warning(FTEXT("A warning message from gamemode"));
}

The KEY to LOCTEXT (first argument) must be unique or you will get a previously hashed string back. If you'd like, you can include a #define that repeats the argument to LOCTEXT twice, as we did earlier:

#define FTEXT(x) LOCTEXT(x, x)

5. Log your messages using the following code:

logger.Info( FTEXT( "Info to log" ) ); 
logger.Warning( FTEXT( "Warning text to log" ) ); 
logger.Error( FTEXT( "Error text to log" ) ); 

This code utilizes the FTEXT() macro we defined earlier. Ensure it is in your codebase.