> For the complete documentation index, see [llms.txt](https://docsv1.polyfrost.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docsv1.polyfrost.org/configuration/creating-your-config/listening-for-option-changes.md).

# Listening for option changes

Monitoring changes to options for any reason is simple, thanks to the convenient methods provided by OneConfig. You can use them like so:

{% tabs %}
{% tab title="Java" %}

```java
public MyConfig() {
    addCallback("myOptionName", () -> {
        System.out.println("myOptionName changed!");
    });
}
```

{% endtab %}

{% tab title="Kotlin" %}

```kotlin
val myOptionName by observable(switch(<...>)) {
    println("myOptionName changed!")
}

val myOptionName by switch(<...>).onChange { println("myOptionName changed!") }
```

{% endtab %}
{% endtabs %}

Easy enough, eh? But what if we want to know the new value at the time of the change?

{% tabs %}
{% tab title="Java" %}

```java
public MyConfig() {
    addCallback<Boolean>("myOptionName", (value) -> {
        System.out.println("myOptionName value: " + value);
    });
}
```

{% endtab %}

{% tab title="Kotlin" %}

```kotlin
val myOptionName by observable(switch(<...>)) {
    println("myOptionName value: $it")
}

val myOptionName by switch(<...>).onChange { println("myOptionName value: $it") }
```

{% endtab %}
{% endtabs %}


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