如何防止 onCreate 在 doAsync 完成之前返回结果
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【中文标题】如何防止 onCreate 在 doAsync 完成之前返回结果【英文标题】：How to prevent onCreate from returning results before doAsync Completes 【发布时间】：2020-11-15 04:17:25 【问题描述】：我在这里需要一些帮助（我是一名新程序员）。我正在用 Kotlin 编写一个应用程序，要求我根据 GPS 位置找到当地的餐馆。找到它们后，我必须将它们归还给用户。我正在处理的特定部分（我已完成地图视图）是餐厅特定详细信息的列表视图。
我遇到的问题是我的 doAsync 任务在 onCreateView （是的，它在一个片段中）返回视图之前没有完成。因此，视图是空白的。我试图让线程休眠，但它会暂停一切，包括异步任务。无论我做什么，当返回视图时，restaurantList.size 始终为 0，并且视图始终为空白。我可以在日志中看到，视图在列表被填充之前返回。我已经为此工作了 2 周。有人可以帮帮我吗？
这是我的 onCreateView 代码：
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View?
val root = inflater.inflate(R.layout.fragment_list, container, false)
fusedLocationClient = LocationServices.getFusedLocationProviderClient(requireActivity())
if (checkPermission(Manifest.permission.ACCESS_COARSE_LOCATION, Manifest.permission.ACCESS_FINE_LOCATION))
fusedLocationClient?.lastLocation?.addOnSuccessListener(requireActivity()) location: Location? ->
if (location == null)
// TODO, handle it
else location.apply
var long = location.longitude
var lat = location.latitude
// Handle location object
var type = "restaurant"
var url = getUrl(lat, long, type)
doAsync
var googlePlacesData = (URL(url).readText())
onComplete
val parser = DataParser()
nearbyPlaceList = parser.parse(googlePlacesData)
for (i in nearbyPlaceList.indices)
val googlePlace = nearbyPlaceList[i]
placeName = googlePlace["place_name"]!!
vicinity = googlePlace["vicinity"]
id = googlePlace["place_id"]
val detailURL = StringBuilder("https://maps.googleapis.com/maps/api/place/details/json?")
detailURL.append("place_id=" + id)
detailURL.append("&key=" + "KEY_GOES_HERE")
doAsync
var detailData = (URL(detailURL.toString()).readText())
onComplete
val jsonObject: JSONObject
val jsonObject2: JSONObject
jsonObject = JSONObject(detailData)
jsonObject2 = jsonObject.getJSONObject("result")
if (!jsonObject2.isNull("name"))
placeName = jsonObject2.getString("name")
if (!jsonObject2.isNull("place_id"))
placeId = jsonObject2.getString("place_id")
if (!jsonObject2.isNull("formatted_address"))
address = jsonObject2.getString("formatted_address")
if (!jsonObject2.isNull("formatted_phone_number"))
phone = jsonObject2.getString("formatted_phone_number")
if (!jsonObject2.isNull("website"))
website = jsonObject2.getString("website")
if (!jsonObject2.isNull("rating"))
rating = jsonObject2.getDouble("rating")
if (bmImg == null)
var jsonPhotosArray: JSONArray? = null
if (jsonObject2.has("photos"))
jsonPhotosArray = jsonObject2.getJSONArray("photos")
val obj = jsonPhotosArray.getJSONObject(0)
photoReference = obj.getString("photo_reference")
val photoURL =
StringBuilder("https://maps.googleapis.com/maps/api/place/photo?")
photoURL.append("maxwidth=500")
photoURL.append("&maxheight=500")
photoURL.append("&key=" + "KEY_GOES_HERE")
photoURL.append("&photoreference=" + photoReference)
doAsync
ImageUrl = URL(photoURL.toString())
val conn =
ImageUrl.openConnection() as HttpURLConnection
conn.setDoInput(true)
conn.connect()
var `is` = conn.getInputStream()
val options = BitmapFactory.Options()
options.inPreferredConfig = Bitmap.Config.RGB_565
bmImg =
BitmapFactory.decodeStream(`is`, null, options)!!
onComplete
var style = "Restaurant"
var openTil = "7 p.m."
var distance = "0.0"
var empsGoing = "2"
restaurantList.add(ListViewModel(placeName,style,address, openTil, distance, empsGoing, rating, phone))
Log.d("Log", "List Total = " + restaurantList.size)
Toast.makeText(requireContext(), "Listing Nearby Restaurants", Toast.LENGTH_SHORT).show()
Log.d("Log", "List Total End= " + restaurantList.size)
val recyclerview = root.findViewById(R.id.rvList) as RecyclerView
recyclerview.layoutManager = LinearLayoutManager(requireActivity())
recyclerview.adapter = RecyclerAdapter(restaurantList, requireContext())
return root
这是我得到的日志输出：
2020-07-25 07:39:47.354 17576-17576/com.mark.lunchappredesign D/Log: Inside onCreate
2020-07-25 07:39:53.415 17576-17576/com.mark.lunchappredesign D/Log: List Total End= 0
2020-07-25 07:39:53.494 17576-17576/com.mark.lunchappredesign D/Log: ListFragment - url = https://maps.googleapis.com/maps/api/place/nearbysearch/json?location=39.812755,-85.7664&radius=5000&type=restaurant&sensor=true&key=KEY_GOES_HERE
2020-07-25 07:39:53.992 17576-17576/com.mark.lunchappredesign D/Log: DataParser - jsonobject ="business_status":"OPERATIONAL","geometry":"location":"lat":39.80146370000001,"lng":-85.7692799,"viewport":"northeast":"lat":39.80274508029151,"lng":-85.7679299197085,"southwest":"lat":39.80004711970851,"lng":-85.7706278802915,"icon":"https:\/\/maps.gstatic.com\/mapfiles\/place_api\/icons\/restaurant-71.png","id":"297878a9f9b57ecb7d7c00c3a695b30ec908c5d4","name":"Subway","opening_hours":"open_now":false,"photos":["height":2988,"html_attributions":["<a href=\"https:\/\/maps.google.com\/maps\/contrib\/116980312202159126535\">Janet Williams<\/a>"],"photo_reference":"CmRaAAAAVQBC5037LqGuRj5bmi0IJg3mYRaZZGWTO--YmFq6iMTRDxWQTEyMILNhI1pjY-T1Ma8Cb_HxvFQc31_Nt-oQv-rOy61APaP5Wytcog
...
...
2020-07-25 07:39:54.918 17576-17576/com.mark.lunchappredesign D/Log: List Total = 1
2020-07-25 07:39:54.931 17576-17576/com.mark.lunchappredesign D/Log: List Total = 2
2020-07-25 07:39:54.942 17576-17576/com.mark.lunchappredesign D/Log: List Total = 3
2020-07-25 07:39:55.022 17576-17576/com.mark.lunchappredesign D/Log: List Total = 4
2020-07-25 07:39:55.034 17576-17576/com.mark.lunchappredesign D/Log: List Total = 5
2020-07-25 07:39:55.034 17576-17576/com.mark.lunchappredesign D/Log: List Total = 6
2020-07-25 07:39:55.083 17576-17576/com.mark.lunchappredesign D/Log: List Total = 7
2020-07-25 07:39:55.091 17576-17576/com.mark.lunchappredesign D/Log: List Total = 8
2020-07-25 07:39:55.126 17576-17576/com.mark.lunchappredesign D/Log: List Total = 9
2020-07-25 07:39:55.131 17576-17576/com.mark.lunchappredesign D/Log: List Total = 10
2020-07-25 07:39:55.172 17576-17576/com.mark.lunchappredesign D/Log: List Total = 11
2020-07-25 07:39:55.183 17576-17576/com.mark.lunchappredesign D/Log: List Total = 12
2020-07-25 07:39:55.194 17576-17576/com.mark.lunchappredesign D/Log: List Total = 13
2020-07-25 07:39:55.203 17576-17576/com.mark.lunchappredesign D/Log: List Total = 14
2020-07-25 07:39:55.273 17576-17576/com.mark.lunchappredesign D/Log: List Total = 15
2020-07-25 07:39:55.278 17576-17576/com.mark.lunchappredesign D/Log: List Total = 16
2020-07-25 07:39:55.310 17576-17576/com.mark.lunchappredesign D/Log: List Total = 17
2020-07-25 07:39:55.410 17576-17576/com.mark.lunchappredesign D/Log: List Total = 18
2020-07-25 07:39:55.611 17576-17576/com.mark.lunchappredesign D/Log: List Total = 19
【问题讨论】：
【参考方案1】：将这部分代码移到onComplete 块中：
Log.d("Log", "List Total End= " + restaurantList.size)
val recyclerview = root.findViewById(R.id.rvList) as RecyclerView
recyclerview.layoutManager = LinearLayoutManager(requireActivity())
recyclerview.adapter = RecyclerAdapter(restaurantList, requireContext())
无论如何，代码显然不是完美的，还有很多需要改进的地方。请注意，无论如何，当您添加Fragment 时，它不一定具有远程数据。通常在创建Fragment 时进行API 调用，然后在onComplete 中，您可以使用数据来填充视图。
【讨论】：
感谢您的帮助和回复。 . .我试过了。 . .当我移动代码时，我收到一条错误消息，告诉我“此处不允许返回”。 。 . .而且，是的，我知道代码需要帮助！ :) 正如我所说，我是编码新手。我想我会“让它工作”然后弄清楚如何清理它！ :) 已编辑。只要让return root留在onCreateView最后一行的代码块之外。
空白屏幕的相同结果！【参考方案2】：
所以，我终于明白了！问题在于“添加”语句的位置！因为我只为每家餐厅下载一张图片，所以我有一个 if 语句来限制那部分代码（if (bmImg == null)）
因此，add 语句只执行了一次。 . .最后添加的餐厅！
感谢大家的帮助，感谢大家的关注！
【讨论】：
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