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# The Command Service |
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[Discord.Commands](xref:Discord.Commands) provides an Attribute-based |
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command parser. |
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## Setup |
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To use Commands, you must create a [Command Service] and a Command |
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Handler. |
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Included below is a very barebone Command Handler. You can extend your |
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Command Handler as much as you like; however, the below is the bare |
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minimum. |
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The `CommandService` will optionally accept a [CommandServiceConfig], |
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which _does_ set a few default values for you. It is recommended to |
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look over the properties in [CommandServiceConfig] and their default |
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values. |
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[!code-csharp[Command Handler](samples/command_handler.cs)] |
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[Command Service]: xref:Discord.Commands.CommandService |
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[CommandServiceConfig]: xref:Discord.Commands.CommandServiceConfig |
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## With Attributes |
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In 1.0, Commands can be defined ahead of time with attributes, or at |
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runtime with builders. |
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For most bots, ahead-of-time Commands should be all you need, and this |
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is the recommended method of defining Commands. |
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### Modules |
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The first step to creating Commands is to create a _module_. |
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A Module is an organizational pattern that allows you to write your |
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Commands in different classes and have them automatically loaded. |
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Discord.Net's implementation of Modules is influenced heavily from |
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ASP.NET Core's Controller pattern. This means that the lifetime of a |
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module instance is only as long as the Command is being invoked. |
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**Avoid using long-running code** in your modules wherever possible. |
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You should **not** be implementing very much logic into your modules, |
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instead, outsource to a service for that. |
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If you are unfamiliar with Inversion of Control, it is recommended to |
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read the MSDN article on [IoC] and [Dependency Injection]. |
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To begin, create a new class somewhere in your project and inherit the |
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class from [ModuleBase]. This class **must** be `public`. |
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>[!NOTE] |
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>[ModuleBase] is an _abstract_ class, meaning that you may extend it |
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>or override it as you see fit. Your module may inherit from any |
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>extension of ModuleBase. |
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By now, your module should look like this: |
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[!code-csharp[Empty Module](samples/empty-module.cs)] |
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[IoC]: https://msdn.microsoft.com/en-us/library/ff921087.aspx |
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[Dependency Injection]: https://msdn.microsoft.com/en-us/library/ff921152.aspx |
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[ModuleBase]: xref:Discord.Commands.ModuleBase`1 |
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### Adding Commands |
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The next step to creating Commands is actually creating the Commands. |
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To create a Command, add a method to your module of type `Task`. |
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Typically, you will want to mark this method as `async`, although it |
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is not required. |
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Adding parameters to a Command is done by adding parameters to the |
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parent Task. |
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For example, to take an integer as an argument from the user, add `int |
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arg`; to take a user as an argument from the user, add `IUser user`. |
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In 1.0, a Command can accept nearly any type of argument; a full list |
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of types that are parsed by default can be found in the below section |
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on _Type Readers_. |
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Parameters, by default, are always required. To make a parameter |
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optional, give it a default value. To accept a comma-separated list, |
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set the parameter to `params Type[]`. |
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Should a parameter include spaces, it **must** be wrapped in quotes. |
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For example, for a Command with a parameter `string food`, you would |
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execute it with `!favoritefood "Key Lime Pie"`. |
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If you would like a parameter to parse until the end of a Command, |
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flag the parameter with the [RemainderAttribute]. This will allow a |
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user to invoke a Command without wrapping a parameter in quotes. |
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Finally, flag your Command with the [CommandAttribute]. (you must |
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specify a name for this Command, except for when it is part of a |
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Module Group - see below) |
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[RemainderAttribute]: xref:Discord.Commands.RemainderAttribute |
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[CommandAttribute]: xref:Discord.Commands.CommandAttribute |
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### Command Overloads |
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You may add overloads to your Commands, and the Command parser will |
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automatically pick up on it. |
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If for whatever reason, you have two Commands which are ambiguous to |
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each other, you may use the @Discord.Commands.PriorityAttribute to |
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specify which should be tested before the other. |
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The `Priority` attributes are sorted in ascending order; the higher |
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priority will be called first. |
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### Command Context |
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Every Command can access the execution context through the [Context] |
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property on [ModuleBase]. `ICommandContext` allows you to access the |
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message, channel, guild, and user that the Command was invoked from, |
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as well as the underlying Discord client that the Command was invoked |
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from. |
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Different types of Contexts may be specified using the generic variant |
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of [ModuleBase]. When using a [SocketCommandContext], for example, the |
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properties on this context will already be Socket entities, so you |
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will not need to cast them. |
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To reply to messages, you may also invoke [ReplyAsync], instead of |
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accessing the channel through the [Context] and sending a message. |
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> [!WARNING] |
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>Contexts should **NOT** be mixed! You cannot have one module that |
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>uses `CommandContext` and another that uses `SocketCommandContext`. |
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[Context]: xref:Discord.Commands.ModuleBase`1#Discord_Commands_ModuleBase_1_Context |
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[SocketCommandContext]: xref:Discord.Commands.SocketCommandContext |
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[ReplyAsync]: xref:Discord.Commands.ModuleBase`1#Discord_Commands_ModuleBase_1_ReplyAsync_System_String_System_Boolean_Discord_Embed_Discord_RequestOptions_ |
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### Example Module |
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At this point, your module should look comparable to this example: |
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[!code-csharp[Example Module](samples/module.cs)] |
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#### Loading Modules Automatically |
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The Command Service can automatically discover all classes in an |
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Assembly that inherit [ModuleBase] and load them. |
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To opt a module out of auto-loading, flag it with |
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[DontAutoLoadAttribute]. |
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Invoke [CommandService.AddModulesAsync] to discover modules and |
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install them. |
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[DontAutoLoadAttribute]: xref:Discord.Commands.DontAutoLoadAttribute |
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[CommandService.AddModulesAsync]: xref:Discord.Commands.CommandService#Discord_Commands_CommandService_AddModulesAsync_Assembly_ |
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#### Loading Modules Manually |
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To manually load a module, invoke [CommandService.AddModuleAsync] by |
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passing in the generic type of your module and optionally, a |
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dependency map. |
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[CommandService.AddModuleAsync]: xref:Discord.Commands.CommandService#Discord_Commands_CommandService_AddModuleAsync__1 |
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### Module Constructors |
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Modules are constructed using Dependency Injection. Any parameters |
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that are placed in the Module's constructor must be injected into an |
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@System.IServiceProvider first. Alternatively, you may accept an |
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`IServiceProvider` as an argument and extract services yourself. |
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### Module Properties |
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Modules with `public` settable properties will have the dependencies |
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injected after the construction of the Module. |
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### Module Groups |
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Module Groups allow you to create a module where Commands are |
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prefixed. To create a group, flag a module with the |
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@Discord.Commands.GroupAttribute. |
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Module groups also allow you to create **nameless Commands**, where |
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the [CommandAttribute] is configured with no name. In this case, the |
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Command will inherit the name of the group it belongs to. |
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### Submodules |
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Submodules are Modules that reside within another one. Typically, |
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submodules are used to create nested groups (although not required to |
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create nested groups). |
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[!code-csharp[Groups and Submodules](samples/groups.cs)] |
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## With Builders |
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**TODO** |
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## Dependency Injection |
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The Command Service is bundled with a very barebone Dependency |
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Injection service for your convenience. It is recommended that you use |
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DI when writing your modules. |
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### Setup |
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First, you need to create an @System.IServiceProvider; you may create |
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your own one if you wish. |
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Next, add the dependencies that your modules will use to the map. |
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Finally, pass the map into the `LoadAssembly` method. Your modules |
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will be automatically loaded with this dependency map. |
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[!code-csharp[IServiceProvider Setup](samples/dependency_map_setup.cs)] |
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### Usage in Modules |
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In the constructor of your Module, any parameters will be filled in by |
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the @System.IServiceProvider that you've passed into `LoadAssembly`. |
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Any publicly settable properties will also be filled in the same |
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manner. |
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>[!NOTE] |
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> Annotating a property with a [DontInjectAttribute] attribute will prevent the |
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property from being injected. |
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>[!NOTE] |
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>If you accept `CommandService` or `IServiceProvider` as a parameter |
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in your constructor or as an injectable property, these entries will |
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be filled by the `CommandService` that the Module is loaded from and |
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the `ServiceProvider` that is passed into it respectively. |
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[!code-csharp[ServiceProvider in Modules](samples/dependency_module.cs)] |
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[DontInjectAttribute]: xref:Discord.Commands.DontInjectAttribute |
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# Preconditions |
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Precondition serve as a permissions system for your Commands. Keep in |
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mind, however, that they are not limited to _just_ permissions and can |
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be as complex as you want them to be. |
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>[!NOTE] |
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>There are two types of Preconditions. |
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[PreconditionAttribute] can be applied to Modules, Groups, or Commands; |
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[ParameterPreconditionAttribute] can be applied to Parameters. |
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[PreconditionAttribute]: xref:Discord.Commands.PreconditionAttribute |
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[ParameterPreconditionAttribute]: xref:Discord.Commands.ParameterPreconditionAttribute |
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## Bundled Preconditions |
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Commands ship with four bundled Preconditions; you may view their |
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usages on their respective API pages. |
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- @Discord.Commands.RequireContextAttribute |
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- @Discord.Commands.RequireOwnerAttribute |
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- @Discord.Commands.RequireBotPermissionAttribute |
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- @Discord.Commands.RequireUserPermissionAttribute |
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## Custom Preconditions |
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To write your own Precondition, create a new class that inherits from |
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either [PreconditionAttribute] or [ParameterPreconditionAttribute] |
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depending on your use. |
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In order for your Precondition to function, you will need to override |
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the [CheckPermissions] method. |
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Your IDE should provide an option to fill this in for you. |
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If the context meets the required parameters, return |
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[PreconditionResult.FromSuccess], otherwise return |
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[PreconditionResult.FromError] and include an error message if |
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necessary. |
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[!code-csharp[Custom Precondition](samples/require_owner.cs)] |
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[CheckPermissions]: xref:Discord.Commands.PreconditionAttribute#Discord_Commands_PreconditionAttribute_CheckPermissions_Discord_Commands_ICommandContext_Discord_Commands_CommandInfo_IServiceProvider_ |
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[PreconditionResult.FromSuccess]: xref:Discord.Commands.PreconditionResult#Discord_Commands_PreconditionResult_FromSuccess |
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[PreconditionResult.FromError]: xref:Discord.Commands.PreconditionResult#Discord_Commands_PreconditionResult_FromError_System_String_ |
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# Type Readers |
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Type Readers allow you to parse different types of arguments in |
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your commands. |
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By default, the following Types are supported arguments: |
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- bool |
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- char |
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- sbyte/byte |
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- ushort/short |
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- uint/int |
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- ulong/long |
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- float, double, decimal |
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- string |
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- DateTime/DateTimeOffset/TimeSpan |
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- IMessage/IUserMessage |
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- IChannel/IGuildChannel/ITextChannel/IVoiceChannel/IGroupChannel |
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- IUser/IGuildUser/IGroupUser |
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- IRole |
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### Creating a Type Readers |
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To create a `TypeReader`, create a new class that imports @Discord and |
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@Discord.Commands and ensure the class inherits from |
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@Discord.Commands.TypeReader. |
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Next, satisfy the `TypeReader` class by overriding the [Read] method. |
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>[!NOTE] |
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>In many cases, Visual Studio can fill this in for you, using the |
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>"Implement Abstract Class" IntelliSense hint. |
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Inside this task, add whatever logic you need to parse the input |
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string. |
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If you are able to successfully parse the input, return |
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[TypeReaderResult.FromSuccess] with the parsed input, otherwise return |
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[TypeReaderResult.FromError] and include an error message if |
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necessary. |
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[TypeReaderResult]: xref:Discord.Commands.TypeReaderResult |
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[TypeReaderResult.FromSuccess]: xref:Discord.Commands.TypeReaderResult#Discord_Commands_TypeReaderResult_FromSuccess_Discord_Commands_TypeReaderValue_ |
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[TypeReaderResult.FromError]: xref:Discord.Commands.TypeReaderResult#Discord_Commands_TypeReaderResult_FromError_Discord_Commands_CommandError_System_String_ |
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[Read]: xref:Discord.Commands.TypeReader#Discord_Commands_TypeReader_Read_Discord_Commands_ICommandContext_System_String_IServiceProvider_ |
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#### Sample |
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[!code-csharp[TypeReaders](samples/typereader.cs)] |
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### Installing TypeReaders |
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TypeReaders are not automatically discovered by the Command Service |
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and must be explicitly added. |
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To install a TypeReader, invoke [CommandService.AddTypeReader]. |
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[CommandService.AddTypeReader]: xref:Discord.Commands.CommandService#Discord_Commands_CommandService_AddTypeReader__1_Discord_Commands_TypeReader_ |
Still Hsu
Christopher F
