我正在開發一個包含片段的 kotlin 應用程式。我正在將使用活動創建的應用程式轉換為片段，但我遇到了問題。運行應用程式時出現錯誤，屬性 fragmentHomeBinding 尚未初始化并且應用程式關閉。
這是片段 Home.kt
class Home : Fragment() {
private lateinit var fusedLocationProviderClient: FusedLocationProviderClient
private lateinit var fragmentHomeBinding: FragmentHomeBinding
@SuppressLint("WrongViewCast")
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
getCurrentLocation()
fragmentHomeBinding.etGetCityName.setOnEditorActionListener { v, actionId, keyEvent ->
if(actionId == EditorInfo.IME_ACTION_SEARCH)
{
getCityWeather(fragmentHomeBinding.etGetCityName.text.toString())
val view = activity?.currentFocus
if(view!=null)
{
val imm:InputMethodManager=
activity?.getSystemService(Context.INPUT_METHOD_SERVICE) as InputMethodManager
imm.hideSoftInputFromWindow(view.windowToken, 0)
fragmentHomeBinding.etGetCityName.clearFocus()
}
true
}
else false
}
}
private fun getCityWeather(cityName:String)
{
fragmentHomeBinding.pbLoading.visibility = View.VISIBLE
ApiUtilities.getApiInterface()?.getCityWeatherData(cityName, API_KEY)?.enqueue(
object:Callback<ModelClass>{
override fun onResponse(call: Call<ModelClass>, response: Response<ModelClass>) {
setDataOnViews((response.body()))
}
override fun onFailure(call: Call<ModelClass>, t: Throwable) {
Toast.makeText(activity?.applicationContext, "Wrong City", Toast.LENGTH_SHORT).show()
}
})
}
private fun getCurrentLocation()
{
if(checkPermission())
{
if(isLocationEnabled())
{
if(ActivityCompat.checkSelfPermission(
requireActivity(), android.Manifest.permission.ACCESS_FINE_LOCATION
) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(
requireActivity(),
android.Manifest.permission.ACCESS_COARSE_LOCATION
) != PackageManager.PERMISSION_GRANTED
){
requestPermission()
return
}
fusedLocationProviderClient.lastLocation.addOnCompleteListener(requireActivity()){ task->
val location: Location?=task.result
if(location==null)
{
fetchCurrentLocationWeather(23.76137119142536.toString(), 90.35059989467042.toString())
}
else
{
fetchCurrentLocationWeather(location.latitude.toString(),location.longitude.toString())
}
}
}
else
{
Toast.makeText(activity?.applicationContext, "Turn on Location", Toast.LENGTH_SHORT).show()
val intent = Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS)
startActivity(intent)
}
}
}
private fun fetchCurrentLocationWeather(latitude: String, longitude:String)
{
fragmentHomeBinding.pbLoading.visibility = View.VISIBLE
ApiUtilities.getApiInterface()?.getCurrentWeatherData(latitude, longitude, API_KEY)?.enqueue(
object : Callback<ModelClass> {
override fun onResponse(call: Call<ModelClass>, response: Response<ModelClass>) {
if(response.isSuccessful)
{
setDataOnViews(response.body())
}
}
override fun onFailure(call: Call<ModelClass>, t: Throwable) {
Toast.makeText(activity?.applicationContext, "ERROR", Toast.LENGTH_SHORT).show()
}
})
}
private fun setDataOnViews(body: ModelClass?) {
val sdf = SimpleDateFormat("dd/MM/yyyy hh:mm")
val currentDate = sdf.format(Date())
fragmentHomeBinding.tvDateTime.text = currentDate
fragmentHomeBinding.tvDayMaxTemp.text = "" kelvinToCelsius(body!!.main.temp_max) "°"
fragmentHomeBinding.tvDayMinTemp.text = "" kelvinToCelsius(body!!.main.temp_min) "°"
fragmentHomeBinding.tvTemp.text = "" kelvinToCelsius(body!!.main.temp)
fragmentHomeBinding.tvFeelsLike.text = "Feels like: " kelvinToCelsius(body!!.main.feels_like) "°"
fragmentHomeBinding.tvWeatherType.text = body.weather[0].main
fragmentHomeBinding.tvPressure.text = body.main.pressure.toString()
fragmentHomeBinding.tvHumidity.text = body.main.humidity.toString() " %"
fragmentHomeBinding.tvWindSpeed.text = body.wind.speed.toString() " m/s"
fragmentHomeBinding.tvCityName.text = body.name
updateUI(body.weather[0].id)
}
private fun updateUI(id: Int) {
fragmentHomeBinding.pbLoading.visibility = View.GONE
fragmentHomeBinding.mainLayout.visibility = View.VISIBLE
}
private fun kelvinToCelsius(temp: Double): Double
{
var intTemp = temp
intTemp = intTemp.minus(273)
return intTemp.toBigDecimal().setScale(1, RoundingMode.UP).toDouble()
}
companion object
{
const val PERMISSION_REQUEST_ACCESS_LOCATION = 100
const val API_KEY = "3c709ccaf2730aa1c263925f75db631a"
}
private fun isLocationEnabled():Boolean{
val locationManager:LocationManager=activity?.getSystemService(Context.LOCATION_SERVICE) as LocationManager
return locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER) || locationManager.isProviderEnabled(
LocationManager.NETWORK_PROVIDER
)
}
private fun requestPermission(){
ActivityCompat.requestPermissions(
requireActivity(), arrayOf(android.Manifest.permission.ACCESS_COARSE_LOCATION,
android.Manifest.permission.ACCESS_FINE_LOCATION),
PERMISSION_REQUEST_ACCESS_LOCATION
)
}
private fun checkPermission():Boolean{
if(ActivityCompat.checkSelfPermission(requireActivity(),
android.Manifest.permission.ACCESS_COARSE_LOCATION) == PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(requireActivity(),
android.Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED)
{
return true
}
return false
}
@Suppress("DEPRECATION")
override fun onRequestPermissionsResult(
requestCode: Int,
permissions: Array<out String>,
grantResults: IntArray
) {
super.onRequestPermissionsResult(requestCode, permissions, grantResults)
if(requestCode== PERMISSION_REQUEST_ACCESS_LOCATION)
{
if(grantResults.isNotEmpty() && grantResults[0] == PackageManager.PERMISSION_GRANTED)
{
Toast.makeText(activity?.applicationContext, "Granted", Toast.LENGTH_SHORT).show()
getCurrentLocation()
}
else{
Toast.makeText(activity?.applicationContext, "Denied", Toast.LENGTH_SHORT).show()
}
}
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
fragmentHomeBinding = DataBindingUtil.inflate(inflater, R.layout.fragment_home, container, false)
// Inflate the layout for this fragment
return fragmentHomeBinding.root
}
}
這是顯示在 logcat 上的錯誤：
2022-05-20 17:45:20.582 22026-22048/com.example.weather D/EGL_emulation: app_time_stats: avg=30.74ms min=18.05ms max=34.54ms count=33
2022-05-20 17:45:21.416 22026-22026/com.example.weather D/AndroidRuntime: Shutting down VM
2022-05-20 17:45:21.417 22026-22026/com.example.weather E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.weather, PID: 22026
kotlin.UninitializedPropertyAccessException: lateinit property fragmentHomeBinding has not been initialized
at com.example.weather.Home.onCreate(Home.kt:58)
at androidx.fragment.app.Fragment.performCreate(Fragment.java:2949)
at androidx.fragment.app.FragmentStateManager.create(FragmentStateManager.java:475)
at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:278)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2189)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:2100)
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:2002)
at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:3138)
at androidx.fragment.app.FragmentManager.dispatchActivityCreated(FragmentManager.java:3072)
at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:251)
at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:502)
at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:246)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1455)
at android.app.Activity.performStart(Activity.java:8076)
at android.app.ActivityThread.handleStartActivity(ActivityThread.java:3660)
at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:221)
at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:201)
at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:173)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:97)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2210)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loopOnce(Looper.java:201)
at android.os.Looper.loop(Looper.java:288)
at android.app.ActivityThread.main(ActivityThread.java:7839)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
2022-05-20 17:45:21.435 22026-22026/com.example.weather I/Process: Sending signal. PID: 22026 SIG: 9
幫助表示贊賞，謝謝。
uj5u.com熱心網友回復：
您的片段視圖系結實體fragmentHomeBinding在onCreateView()生命周期方法中初始化。但是您正在以onCreate()生命周期方法訪問。在 Fragment 生命周期中，onCreate()會在之前呼叫onCreatedView()。
結果，您正在訪問一個未初始化的物件。要解決此問題，請將 onCreate() 中的視圖系結參考代碼移動到 onCreateView()，如下所示。
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
fragmentHomeBinding = DataBindingUtil.inflate(inflater, R.layout.fragment_home, container, false)
fragmentHomeBinding.etGetCityName.setOnEditorActionListener { v, actionId, keyEvent ->
if(actionId == EditorInfo.IME_ACTION_SEARCH)
{
getCityWeather(fragmentHomeBinding.etGetCityName.text.toString())
val view = activity?.currentFocus
if(view!=null)
{
val imm:InputMethodManager=
activity?.getSystemService(Context.INPUT_METHOD_SERVICE) as InputMethodManager
imm.hideSoftInputFromWindow(view.windowToken, 0)
fragmentHomeBinding.etGetCityName.clearFocus()
}
true
}
else false
}
// Inflate the layout for this fragment
return fragmentHomeBinding.root
}
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