android - 如果 null 其他不起作用

Question

如果 location 为空，我想执行一个消息，如果不为空，我想执行另一个消息，所以我正在尝试使用 elvis-operator作为 a?.let{} ?: run{} 语句，但是 run 部分不可访问，它告诉我它不是必需的，也不是不可空的!

我遇到错误的函数是:

getLocation(
           context,
                { location ->
                    location?.let {
                        msg = ("As of: ${Date(it.time)}, " +
                                "I am at: http://maps.google.com/?q=@" +
                                "${it.latitude}, ${it.longitude}, " +
                                "my speed is: ${it.speed}")
                    } ?: run { . // Getting error here
                        msg = "Sorry, it looks GPS is off, no location found\""
                    }

                    sendSMS(
                            context,
                            address,
                            msg,
                            subId
                    )
                }
        )

getLocation 函数是:

object UtilLocation {
    private lateinit var l : Location

    @SuppressLint("MissingPermission")
    fun getLocation(context: Context, callback: (Location) -> Unit) {
        fusedLocationClient = LocationServices.getFusedLocationProviderClient(context!!)

        fusedLocationClient.lastLocation
                .addOnSuccessListener { location : Location? ->
                    this.l = location!!
                    callback.invoke(this.l)
                }
    }
}

Answer 1

在fun getLocation(context: Context, callback: (Location) -> Unit)中，callback的参数Location为NotNull，所以它永远不会为空，这就是 location?.let 导致警告的原因——它永远不会为空，所以不可能输入表达式的 ?: run 部分。

据我所知，您需要此代码(回调 的参数可空，删除不必要的 NotNull 断言，添加空检查而不是断言):

object UtilLocation {
    private lateinit var l : Location

    @SuppressLint("MissingPermission")
    fun getLocation(context: Context, callback: (Location?) -> Unit) {
        fusedLocationClient = LocationServices.getFusedLocationProviderClient(context)
        fusedLocationClient.lastLocation
                .addOnSuccessListener { location : Location? ->
                    if (location != null) this.l = location
                    callback.invoke(this.l)
                }
    }
}

现在这段代码可以工作了。我做了一些重构，让它看起来更漂亮

getLocation(context) { location ->
    msg = location?.let {
        "As of: ${Date(it.time)}, " +
                "I am at: http://maps.google.com/?q=@" +
                "${it.latitude}, ${it.longitude}, " +
                "my speed is: ${it.speed}"
    } ?: run {
        "Sorry, it looks GPS is off, no location found\""
    }

    sendSMS(context, address, msg, subId)
}