# Custom Commands

Command represents a single operation, that controls what happens on the scene; e.g., it can be used to change a background, move a character or load another naninovel script. Parametrized command sequences defined in naninovel scripts effectively controls the game flow. You can find available built-in commands in the API reference. In code, all the built-in script command implementations are defined under Naninovel.Commands namespace.

# Adding Custom Command

To add your own custom script command, create a new C# class derived from Command and implement ExecuteAsync abstract method. The created class will automatically be picked up by the engine and you'll be able to invoke the command from the naninovel scripts by either the class name or an alias (if assigned). To assign an alias to the naninovel command, apply CommandAlias attribute to the class.

WARNING

When adding custom implementation types under a non-predefined assembly (via assembly definitions), add the assembly name to the Type Assemblies list found in the engine configuration menu. Otherwise, the engine won't be able to locate your custom types.

ExecuteAsync is an async method invoked when the command is executed by the scripts player; put the command logic there. Use engine services to access the engine built-in systems. Naninovel script execution will halt until this method returns a completed task in case Wait parameter is true.

To expose a command parameter to naninovel scripts, add a public field to the command class with one of the supported types:

Field Type	Value Type	Script Example
StringParameter	String	`LoremIpsum`, `"Lorem ipsum"`
IntegerParameter	Int32	`10`, `0`, `-1`
DecimalParameter	Single	`0.525`, `-55.1`
BooleanParameter	Boolean	`true`, `false`
NamedStringParameter	NamedString	`Script001.LabelName`, `.LabelName`
NamedIntegerParameter	NamedInteger	`Yuko.5`
NamedDecimalParameter	NamedFloat	`Kohaku.-10.25`
NamedBooleanParameter	NamedBoolean	`Misaki.false`
StringListParameter	List<String>	`Lorem,ipsum,"doler sit amet"`
IntegerListParameter	List<Int32>	`10,-1,0`
DecimalListParameter	List<Single>	`0.2,10.5,-88.99`
BooleanListParameter	List<Boolean>	`true,false,true`
NamedStringListParameter	List<NamedString>	`Felix.Happy,Jenna.Confidence`
NamedIntegerListParameter	List<NamedInteger>	`Yuko.5,Misaki.-8`
NamedDecimalListParameter	List<NamedFloat>	`Nanikun.88.99,Yuko.-5.1`
NamedBooleanListParameter	List<NamedBoolean>	`Misaki.false,Kohaku.true`

Optionally, you can apply [ParameterAlias] attribute to the field to assign an alias name to the parameter allowing it to be used instead of the field name when referencing the parameter in naninovel scripts. If you wish to make the parameter nameless, set NamelessParameterAlias constant (empty string) as the alias; please note, that only one nameless parameter is allowed per command.

To make parameter required (causing an error to be logged when it's not specified in naninovel script), apply [RequiredParameter] attribute to the field. When the attribute is not applied, parameter is considered optional.

All the parameter types have HasValue property, which you can use to test whether the parameter has been assigned in naninovel script; optionally, you can use Assigned() static method, which takes a parameter instance and returns true when the provided parameter is not null and has a value assigned.

In case execution of the command requires loading some resources, implement Command.IPreloadable interface to preload the required resources when the game is loading; find more about memory management in the resource providers guide.

In case the command has parameters that can be localized (text directly presented to the user, usually), implement Command.ILocalizable interface to add the command to the generated script localization documents.

You can find scripts with all the built-in command implementations at Naninovel/Runtime/Commands package folder; feel free to use them as a reference when implementing your own custom commands.

Below is an example of a custom command, that can be invoked from naninovel scripts as @HelloWorld or @hello to print "Hello World!" to the console and can also take an optional name parameter (eg, @hello name:Felix) to greet the provided name instead of the world.

using Naninovel;
using Naninovel.Commands;
using UnityEngine;

[CommandAlias("hello")]
public class HelloWorld : Command
{
    public StringParameter Name;

    public override UniTask ExecuteAsync (AsyncToken asyncToken = default)
    {
        if (Assigned(Name))
        {
            Debug.Log($"Hello, {Name}!");
        }
        else
        {
            Debug.Log("Hello World!");
        }

        return UniTask.CompletedTask;
    }
}

EXAMPLE

Another example of adding custom commands to add/remove items of an inventory system can be found in the inventory example project on GitHub.

Specifically, the command implementations are stored at Runtime/Commands directory.

# AsyncToken

Notice the optional AsyncToken argument provided for the ExecuteAsync method. When performing async operations, make sure to check the token for cancellation and completion requests after each async operation and react accordingly:

AsyncToken.Canceled means the engine has been destroyed or reset; in both cases it's no longer safe to use the engine APIs and any state mutations will lead to an undefined behaviour. When canceled, the command implementation is expected to throw AsyncOperationCanceledException immediately, discarding any currently performed activities.
AsyncToken.Completed means the command is expected to complete all the activities as fast as possible; eg, if you're running animations, finish them instantly, no matter the expected duration. This usually happens when player activates continue input or a save game operation is started.

public override async UniTask ExecuteAsync (AsyncToken asyncToken = default)
{
    await PerformSomethingAsync();
    // The engine may have been destroyed while the above async method been running;
    // below will check and throw the exception if that's the case.
    asyncToken.ThrowIfCanceled();
    // It's safe to continue using the Engine APIs after the check.
    var someUI = Engine.GetService<IUIManager>().GetUI<SomeUI>();
    // In case completion is requested, fade the UI instantly.
    var fadeDuration = asyncToken.Completed ? 0 : 5;
    await someUI.ChangeVisibilityAsync(false, fadeDuration, asyncToken);
    // Notice the method above accepted the async token; such methods will handle
    // the cancellations internally, freeing you from checking after awaiting them.
}

# Overriding Built-In Command

In some cases it could be useful to override built-in Naninovel commands. For example, you may want to change how @print commands work without adding a custom one, so that the change will also affect generic text lines (text from the generic lines is parsed into the print commands under the hood).

To override a built-in command, add a custom one and apply the same alias built-in command has. Reimport the naninovel scripts (right-click over a folder they're stored at, then click "Reimport") after overriding a command in order for the changes to take effect. The custom command will then automatically be used instead of the built-in one when playing a naninovel script.

Below is an example of overriding built-in @print command, so that the printed text will be logged into the console before being revealed to the player.

[CommandAlias("print")]
public class MyCustomPrintCommand : PrintText
{
    public override UniTask ExecuteAsync (AsyncToken asyncToken = default)
    {
        Debug.Log(Text);
        return base.ExecuteAsync(asyncToken);
    }
}

EXAMPLE

Find a more useful example of overriding built-in commands on the forum. An overridden and custom commands will allow changing reveal speed right inside generic text lines, eg:

Yuko: [s 0.1] Print text 10 times slower than usual. [s 2] Print 2 times faster.

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