科特林与地图Android中

Question

override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View { 
var view: View = inflater?.inflate(R.layout.map_fragment, null)!! 

var mapFragment : SupportMapFragment?=null 
mapFragment= fragmentManager.findFragmentById(R.id.map) as SupportMapFragment 
mapFragment.getMapAsync(this) 

return view 
} 

的logcat：

FATAL EXCEPTION: main 
kotlin.TypeCastException: null cannot be cast to non-null type 
com.google.android.gms.maps.SupportMapFragment 
at example.com.kotlinexamplebydimple.Mapfragment.onCreateView(Mapfragment.kt:36) 

在此线路上错误显示：

mapFragment= fragmentManager.findFragmentById(R.id.map) as SupportMapFragment 

Answer 1

你宣布mapFragment为可以为空，所以你不得不面对它：

var mapFragment : SupportMapFragment?=null 
mapFragment = fragmentManager.findFragmentById(R.id.map) as SupportMapFragment? 
mapFragment?.getMapAsync(this) 

Answer 2

错误意味着您试图将null投射到SupportMapFragment。所以，首先检查类型会更安全。

val mapFragment = fragmentManager.findFragmentById(R.id.map) 
if (mapFragment is SupportMapFragment) { 
    mapFragment.getMapAsync(this) 
}