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.
The CommandService optionally will 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.
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 invoked.
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 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 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, add int arg. To take
a user as an argument, 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 of your commands, and the command parser will
automatically pick up on it.
If, for whatever reason, you have too commands which are ambiguous to
each other, you may use the @Discord.Commands.PriorityAttribute to
specify which should be tested before the other.
Priority's are sorted in ascending order; the higher priority will be
called first.
CommandContext
Every command can access the execution context through the Context
property on ModuleBase. CommandContext allows you to access the
message, channel, guild, and user that the command was invoked from,
as well as the underlying discord client 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. 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 constructor must be injected into an
@Discord.Commands.IDependencyMap. Alternatively, you may accept an
IDependencyMap as an argument and extract services yourself.
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 module. 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 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
Commands ships with four bundled preconditions; you may view their
usages on their API page.
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.
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:
- 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. Ensure your class inherits from @Discord.Commands.TypeReader
Next, satisfy the TypeReader class by overriding Read.
[!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.
