Kotlin：等待异步调用完成，然后将值分配给 var 然后返回

Question

I have a variable loginToken . I want to assign value to is as

var loginToken: String = getLoginToken()

Following is my getLoginToken function

private fun getLoginToken(context: Context): String {
    val sharedPref: SharedPreferences = context.getSharedPreferences(PREF_NAME, PRIVATE_MODE)
    var token =  sharedPref.getString("token", null)
    if (token == null) {
        token = LoginManager(activity).getToken(onGetSuccess = {
                // I get token here, i want to assign it to token var
             }, onGetFailure = {
                // I want to set token as empty string
             })
    }
    return token
}

How should I assign value to token and finally return it only when I get the result of getToken call?

Answer 1

You can use suspendCancellableCoroutine to convert a callback approach to coroutines. So for a coroutine approach, we can do something like this:

private fun getLoginToken(context: Context): String {
    val sharedPref: SharedPreferences = context.getSharedPreferences(PREF_NAME, PRIVATE_MODE)
    var token = sharedPref.getString("token", null)
    if (token == null) {
        token = runBlocking { getTokenFromActivity(activity) }
    }
    return token
}

private suspend fun getTokenFromActivity(activity: Activity) =
    suspendCancellableCoroutine {
            LoginManager(activity).getToken(onGetSuccess = {
                it.completeResume(result)
            }, onGetFailure = {
                it.completeResume("")
            })
        }

You can also use a locking approach. For example, using a CountdownLatch . (lock it before the getToken function and unlock when the result is ready in the callback.)