Why can't I call kotlin suspend function under lambda function

Question

Let me start with example code snippets

suspend fun executeLive(result: MutableLiveData<Person>) {

    val response = ... //suspend api request

    mediatorLiveData.removeSource(response)

    mediatorLiveData.addSource(response) {
        result.value = sortData(it) // sortData is also suspend function which sortData at Dispatcher.Default
    }

}

In this example, sortData can't call under lambda function(in this case addSource).And also I already declare executeLive as suspend, that why suspend api request can start at first. But sortData function show compile time error

Suspend function can only be called from a coroutine body

So how do I change my code structure to solve this problems?

Update: Is there any article about this?

Answer 1

A lambda is generally a callback function. Callback functions are so called because we wrap a block of code in a function, and pass it to someone else (or some place else) to be executed. It is a basic inversion of control where the code is not for you to execute, but someone else to do it (example the framework).

For example when you set a onClickListener on a button, we don't know when it will get called, we pass a lambda for the framework which takes care of the user interaction to call the specified action.

In your case similarly the suspend function is not calling the sortdata, it is passing it to the mediatorLiveData object to call it in its own context. It is not necessary the lambda you passed would be called from a coroutine body, as such this is not allowed.