Discord.Net/docs/guides/commands/commands.md

The Command Service

Discord.Commands provides an Attribute-based command parser.

Setup

To use Commands, you must create a Command Service and a Command Handler.

Included below is a very barebone Command Handler. You can extend your Command Handler as much as you like; however, the below is the bare minimum.

The CommandService will optionally accept a CommandServiceConfig, which does set a few default values for you. It is recommended to look over the properties in CommandServiceConfig and their default values.

[!code-csharpCommand Handler]

With Attributes

In 1.0, Commands can be defined ahead of time with attributes, or at runtime with builders.

For most bots, ahead-of-time Commands should be all you need, and this is the recommended method of defining Commands.

Modules

The first step to creating Commands is to create a module.

A Module is an organizational pattern that allows you to write your Commands in different classes and have them automatically loaded.

Discord.Net's implementation of Modules is influenced heavily from ASP.NET Core's Controller pattern. This means that the lifetime of a module instance is only as long as the Command is being invoked.

Avoid using long-running code in your modules wherever possible. You should not be implementing very much logic into your modules, instead, outsource to a service for that.

If you are unfamiliar with Inversion of Control, it is recommended to read the MSDN article on IoC and Dependency Injection.

To begin, create a new class somewhere in your project and inherit the class from ModuleBase. This class must be public.

Note

ModuleBase is an abstract class, meaning that you may extend it or override it as you see fit. Your module may inherit from any extension of ModuleBase.

By now, your module should look like this:

[!code-csharpEmpty Module]

Adding Commands

The next step to creating Commands is actually creating the Commands.

To create a Command, add a method to your module of type Task. Typically, you will want to mark this method as async, although it is not required.

Adding parameters to a Command is done by adding parameters to the parent Task.

For example, to take an integer as an argument from the user, add int arg; to take a user as an argument from the user, add IUser user. In 1.0, a Command can accept nearly any type of argument; a full list of types that are parsed by default can be found in the below section on Type Readers.

Parameters, by default, are always required. To make a parameter optional, give it a default value. To accept a comma-separated list, set the parameter to params Type[].

Should a parameter include spaces, it must be wrapped in quotes. For example, for a Command with a parameter string food, you would execute it with !favoritefood "Key Lime Pie".

If you would like a parameter to parse until the end of a Command, flag the parameter with the RemainderAttribute. This will allow a user to invoke a Command without wrapping a parameter in quotes.

Finally, flag your Command with the CommandAttribute (you must specify a name for this Command, except for when it is part of a Module Group - see below).

Command Overloads

You may add overloads to your Commands, and the Command parser will automatically pick up on it.

If for whatever reason, you have two Commands which are ambiguous to each other, you may use the @Discord.Commands.PriorityAttribute to specify which should be tested before the other.

The Priority attributes are sorted in ascending order; the higher priority will be called first.

Command Context

Every Command can access the execution context through the Context property on ModuleBase. ICommandContext allows you to access the message, channel, guild, and user that the Command was invoked from, as well as the underlying Discord client that the Command was invoked from.

Different types of Contexts may be specified using the generic variant of ModuleBase. When using a SocketCommandContext, for example, the properties on this context will already be Socket entities, so you will not need to cast them.

To reply to messages, you may also invoke ReplyAsync, instead of accessing the channel through the Context and sending a message.

Warning

Contexts should NOT be mixed! You cannot have one module that uses CommandContext and another that uses SocketCommandContext.

Example Module

At this point, your module should look comparable to this example: [!code-csharpExample Module]

Loading Modules Automatically

The Command Service can automatically discover all classes in an Assembly that inherit ModuleBase and load them.

To opt a module out of auto-loading, flag it with DontAutoLoadAttribute.

Invoke CommandService.AddModulesAsync to discover modules and install them.

Loading Modules Manually

To manually load a module, invoke CommandService.AddModuleAsync by passing in the generic type of your module and optionally, a dependency map.

Module Constructors

Modules are constructed using Dependency Injection. Any parameters that are placed in the Module's constructor must be injected into an @System.IServiceProvider first. Alternatively, you may accept an IServiceProvider as an argument and extract services yourself.

Module Properties

Modules with public settable properties will have the dependencies injected after the construction of the Module.

Module Groups

Module Groups allow you to create a module where Commands are prefixed. To create a group, flag a module with the @Discord.Commands.GroupAttribute.

Module groups also allow you to create nameless Commands, where the CommandAttribute is configured with no name. In this case, the Command will inherit the name of the group it belongs to.

Submodules

Submodules are Modules that reside within another one. Typically, submodules are used to create nested groups (although not required to create nested groups).

[!code-csharpGroups and Submodules]

With Builders

TODO

Dependency Injection

The Command Service is bundled with a very barebone Dependency Injection service for your convenience. It is recommended that you use DI when writing your modules.

Setup

First, you need to create an @System.IServiceProvider; you may create your own one if you wish.

Next, add the dependencies that your modules will use to the map.

Finally, pass the map into the LoadAssembly method. Your modules will be automatically loaded with this dependency map.

[!code-csharpIServiceProvider Setup]

Usage in Modules

In the constructor of your Module, any parameters will be filled in by the @System.IServiceProvider that you've passed into LoadAssembly.

Any publicly settable properties will also be filled in the same manner.

Note

Annotating a property with a DontInjectAttribute attribute will prevent the property from being injected.

Note

If you accept CommandService or IServiceProvider as a parameter in your constructor or as an injectable property, these entries will be filled by the CommandService that the Module is loaded from and the ServiceProvider that is passed into it respectively.

[!code-csharpServiceProvider in Modules]

Preconditions

Precondition serve as a permissions system for your Commands. Keep in mind, however, that they are not limited to just permissions and can be as complex as you want them to be.

Note

There are two types of Preconditions. PreconditionAttribute can be applied to Modules, Groups, or Commands; ParameterPreconditionAttribute can be applied to Parameters.

Bundled Preconditions

Commands ship with four bundled Preconditions; you may view their usages on their respective API pages.

• @Discord.Commands.RequireContextAttribute
• @Discord.Commands.RequireOwnerAttribute
• @Discord.Commands.RequireBotPermissionAttribute
• @Discord.Commands.RequireUserPermissionAttribute

Custom Preconditions

To write your own Precondition, create a new class that inherits from either PreconditionAttribute or ParameterPreconditionAttribute depending on your use.

In order for your Precondition to function, you will need to override the CheckPermissions method.

Your IDE should provide an option to fill this in for you.

If the context meets the required parameters, return PreconditionResult.FromSuccess, otherwise return PreconditionResult.FromError and include an error message if necessary.

[!code-csharpCustom Precondition]

Type Readers

Type Readers allow you to parse different types of arguments in your commands.

By default, the following Types are supported arguments:

• bool
• char
• sbyte/byte
• ushort/short
• uint/int
• ulong/long
• float, double, decimal
• string
• DateTime/DateTimeOffset/TimeSpan
• IMessage/IUserMessage
• IChannel/IGuildChannel/ITextChannel/IVoiceChannel/IGroupChannel
• IUser/IGuildUser/IGroupUser
• IRole

Creating a Type Readers

To create a TypeReader, create a new class that imports @Discord and @Discord.Commands and ensure the class inherits from @Discord.Commands.TypeReader.

Next, satisfy the TypeReader class by overriding the Read method.

Note

In many cases, Visual Studio can fill this in for you, using the "Implement Abstract Class" IntelliSense hint.

Inside this task, add whatever logic you need to parse the input string.

If you are able to successfully parse the input, return TypeReaderResult.FromSuccess with the parsed input, otherwise return TypeReaderResult.FromError and include an error message if necessary.

Sample

[!code-csharpTypeReaders]

Installing TypeReaders

TypeReaders are not automatically discovered by the Command Service and must be explicitly added.

To install a TypeReader, invoke CommandService.AddTypeReader.