How do i bind and invoke`function type` in android data binding?

Question

I've a variable of type (position: Int) -> Unit and I want to invoke the method from xml like this android:onClick="@{theMethod.invoke(someInt)}

Is it possible?, then How can I do it ?

Answer 1

The way I went about it is as follows. The method you have will correspond to the class kotlin.jvm.functions.Function1. so the idea is to declare this in the XML as such:

<data>
    <import type="kotlin.jvm.functions.Function1"/>
    <import type="kotlin.Unit"/>

    <variable
        name="theMethod"
        type="Function1&lt;Integer, Unit>"/>
</data>

It doesn't look pretty, but it works. We import what we want and then declare a binding variable of the type we want. Note that the character < is illegal when trying to define generic types, so we use <.

Now it should be easy to use. I do it like:

android:onClick="@{_ -> theMethod.invoke(someInt)}"

The method signature for onClick requires us to pass in a method that receives one parameter of type View. I'm not interested in using it, so I declare it as _ in the lambda I pass to the onClick. Then inside the lambda I invoke the method I want.

I always make an effort not to put logic inside the XML, but I allow myself these kind of shortcuts, since I don't really think of them as business logic.

Hope it helps.

Answer 2

Use the lambda form

android:onClick="@{() -> theMethod.invoke(someInt)}