# Developer API
ViaFabricPlus provides various events and APIs for developers to use. This page explains how to use them.

## Events
ViaFabricPlus events are using the [Fabric Event API](https://fabricmc.net/wiki/tutorial:events). You can register to them like this:
```java
ChangeProtocolVersionCallback.EVENT.register((oldVersion, newVersion) -> {
    System.out.println("Version changed to " + newVersion.getName());
});
```
### ViaFabricPlus has 8 events at the moment
| Callback class name                  | Description                                                                                                                                                                                                   |
|--------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| ChangeProtocolVersionCallback        | Called when the user changes the target version in the screen, or if you connect to a server for which a specific version has been selected, you disconnect, the event for the actual version is also called. |
| DisconnectCallback                   | Called when the user disconnects from a server                                                                                                                                                                |
| LoadCallback                         | Called at the earliest point ViaFabricPlus is injecting too                                                                                                                                                   |
| LoadClassicProtocolExtensionCallback | Called when the classic server sends the protocol extensions (only in **c0.30 CPE**)                                                                                                                          |
| PostGameLoadCallback                 | Called when Minecraft is finished with loading all its components                                                                                                                                             |
| PostViaVersionLoadCallback           | Called when ViaVersion is loaded and ready to use                                                                                                                                                             |
| RegisterSettingsCallback             | Called after the default setting groups are loaded and before the setting config is loaded                                                                                                                    |
| LoadSaveFilesCallback                | Called before and after the save files are loaded                                                                                                                                                             |

## Get and set the current protocol version
```java
final VersionEnum version = ProtocolHack.getTargetVersion();
if (version == VersionEnum.r1_8) {
    ProtocolHack.setTargetVersion(VersionEnum.r1_9);
}
```

## Get a Minecraft ClientConnection by channel
```java
final ClientConnection connection = channel.attr(ProtocolHack.CLIENT_CONNECTION_ATTRIBUTE_KEY).get();
```

## Interact with UserConnection objects
```java
// If ViaVersion is translating, this field will return the user connection of the client
final UserConnection userConnection = ProtocolHack.getPlayNetworkUserConnection();

// If you need a dummy user connection for testing, you can use this method
final UserConnection cursedDummy = ProtocolHack.createDummyUserConnection(ProtocolHack.NATIVE_VERSION, VersionEnum.r1_18_2);
// The cursedDummy field now contains all protocols from the native version to 1.18.2
```

## ViaVersion internals
### Add CustomPayload channels for versions below 1.13
In order to receive custom payloads with custom channels in versions below 1.13, you need to register them, that's what you do:
```java
Protocol1_13To1_12_2.MAPPINGS.getChannelMappings().put("FML|HS", "fml:hs");
```

### Check if an item exists in a specific version
```java
final VersionRange range = ItemRegistryDiff.ITEM_DIFF.get(Items.WRITABLE_BOOK); // If an item does not appear in the item map, it has always existed

// The Range class then contains all versions in which the item occurs. 
// https://github.com/ViaVersion/ViaLoader
if (ItemRegistryDiff.contains(Items.STONE, VersionRange.andOlder(VersionEnum.r1_8))) {
    // Do something
}
```

### Creating own settings for the settings screen
```java
public class ExampleSettingGroup extends SettingGroup {
    
    private static final ExampleSettingGroup instance = new ExampleSettingGroup();
    
    public final BooleanSetting test = new BooleanSetting(this, Text.of("Test"), false);
    
    public ExampleSettingGroup() {
        super("Example");
    }
    
    public static ExampleSettingGroup global() {
        return instance;
    }
    
}
```

and then you register the setting group in your onLoad method
```java
RegisterSettingsCallback.EVENT.register(state -> {
    if (state == RegisterSettingsCallback.State.POST) {
        ViaFabricPlus.global().getSettingsManager().addGroup(ExampleSettingGroup.INSTANCE);
    }
});
```