Discord.Net/docs/guides/commands.md

The Command Service

Discord.Commands provides an Attribute-based Command Parser.

Setup

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

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

[!code-csharpBarebones Command Handler]

Commands

In 1.0, Commands are no longer implemented at runtime with a builder pattern. While a builder pattern may be provided later, commands are created primarily with attributes.

Basic Structure

All commands belong to a Module. (See the below section for creating modules).

All commands in a module must be defined as a Task.

To add parameters to your command, you simply need to add parameters to the Task that represents the command. You are not required to accept all arguments as String, they will be automatically parsed
into the type you specify for the arument. See the Example Module for an example of command parameters.

Modules

Modules are an organizational pattern that allow 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 being ran in it.

Avoid using long-running code in your modules whereever possible. You should not be implementing very much logic into your modules; 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 create a module, create a class that inherits from @Discord.Commands.ModuleBase.

Example Module

[!code-csharpModules]

Loading Modules Automatically

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

To have a module opt-out of auto-loading, pass autoload: false in the Module attribute.

Invoke CommandService.AddModules to discover modules and install them.

Loading Modules Manually

To manually load a module, invoke CommandService.AddModule, 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 constructor must be injected into an @Discord.Commands.IDependencyMap. Alternatively, you may accept an IDependencyMap as an argument and extract services yourself.

Command Groups

Command Groups allow you to create a module where commands are prefixed. To create a group, create a new module and flag it with the @Discord.Commands.GroupAttribute.

Note

Groups do not need to be modules. Only classes with commands should inherit from ModuleBase. If you plan on using a group for strictly organizational purposes, there is no reason to make it a module.

[!code-csharpGroups Sample]

Dependency Injection

The commands service is bundled with a very barebones Dependency Injection service for your convienence. It is recommended that you use DI when writing your modules.

Setup

First, you need to create an @Discord.Commands.IDependencyMap. The library includes @Discord.Commands.DependencyMap to help with this, however you may create your own IDependencyMap if you wish.

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

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

[!code-csharpDependencyMap Setup]

Usage in Modules

In the constructor of your module, any parameters will be filled in by the @Discord.Commands.IDependencyMap you pass into LoadAssembly.

Note

If you accept CommandService or IDependencyMap as a parameter in your constructor, these parameters will be filled by the CommandService the module was loaded from, and the DependencyMap passed into it, respectively.

[!code-csharpDependencyMap in Modules]

Preconditions

Preconditions 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

Preconditions can be applied to Modules, Groups, or Commands.

Bundled Preconditions

@Discord.Commands ships with two built-in preconditions, @Discord.Commands.RequireContextAttribute and @Discord.Commands.RequirePermissionAttribute.

RequireContext

@Discord.Commands.RequireContextAttribute is a precondition that requires your command to be executed in the specified context.

You may require three different types of context:

• Guild
• DM
• Group

Since these are Flags, you may OR them together.

[!code-csharpRequireContext]

RequirePermission

@Discord.Commands.RequirePermissionAttribute is a precondition that allows you to quickly specfiy that a user must poesess a permission to execute a command.

You may require either a @Discord.GuildPermission or @Discord.ChannelPermission

[!code-csharpRequireContext]

Custom Preconditions

To write your own preconditions, create a new class that inherits from @Discord.Commands.PreconditionAttribute

In order for your precondition to function, you will need to override CheckPermissions, which is a Task<PreconditionResult>. Your IDE should provide an option to fill this in for you.

Return PreconditionResult.FromSuccess() if the context met the required parameters, otherwise return PreconditionResult.FromError(), optionally including an error message.

[!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:

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

Creating a Type Readers

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

Next, satisfy the TypeReader class by overriding Task<TypeReaderResult> Read(CommandContext context, string input).

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.

Finally, return a TypeReaderResult. If you were able to successfully parse the input, return TypeReaderResult.FromSuccess(parsedInput). Otherwise, return TypeReaderResult.FromError.

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.