GoogleMap 和 ViewModel

Question

我有一个包含片段作为地图的屏幕

XML

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

    <androidx.appcompat.widget.Toolbar
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="@color/design_default_color_background"
            android:fitsSystemWindows="true"
            android:minHeight="?attr/actionBarSize"
            app:theme="@style/ToolbarColoredBackArrow">

        <androidx.constraintlayout.widget.ConstraintLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent">

            <ImageView
                    android:id="@+id/imageView_back"
                    android:layout_width="48dp"
                    android:layout_height="48dp"
                    android:padding="12dp"
                    app:layout_constraintStart_toStartOf="parent"
                    app:layout_constraintTop_toTopOf="parent"
                    app:srcCompat="@drawable/back" />

            <TextView
                    android:id="@+id/toolbar_title"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_gravity="center"
                    android:layout_marginStart="8dp"
                    android:layout_marginLeft="8dp"
                    android:layout_marginEnd="8dp"
                    android:layout_marginRight="8dp"
                    android:textColor="@color/colorTextBlack"
                    android:textSize="18sp"
                    app:layout_constraintBottom_toBottomOf="parent"
                    app:layout_constraintEnd_toEndOf="parent"
                    app:layout_constraintStart_toStartOf="parent"
                    app:layout_constraintTop_toTopOf="parent" />

        </androidx.constraintlayout.widget.ConstraintLayout>

    </androidx.appcompat.widget.Toolbar>

    <fragment
        app:layout_constraintTop_toBottomOf="@id/toolbar"
        app:layout_constraintBottom_toTopOf="@id/ll_bottom"
        android:id="@+id/googleMap"
        class="com.google.android.gms.maps.SupportMapFragment"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        />

    <LinearLayout
        android:id="@+id/ll_bottom"
        app:layout_constraintBottom_toBottomOf="parent"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="4dp"
        android:gravity="center">
        <View
            app:layout_constraintBottom_toBottomOf="parent"
            android:layout_width="100dp"
            android:layout_height="8dp"
            android:background="@drawable/bottom_sheet_divider"/>
    </LinearLayout>
</androidx.constraintlayout.widget.ConstraintLayout>

在OnViewCreated中，我先设置map，再设置viewModel 然后我才得到包并在 viewModel 中设置值以观察变量

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        setupMap()

        viewModel = ViewModelProvider(requireActivity(), viewModelFactory).get(MapNewTwoViewModel::class.java)

        setupViewModel()
        getBundle()
    }

SetupMap 没有什么特别之处

private fun setupMap(){

        val fragment = childFragmentManager.findFragmentById(R.id.googleMap) as SupportMapFragment

        fragment.getMapAsync(this)

    }

override fun onMapReady(map: GoogleMap?) {
        googleMap = map
        googleMap?.uiSettings?.isMyLocationButtonEnabled = true
        googleMap?.uiSettings?.isZoomControlsEnabled = true
        googleMap?.uiSettings?.isCompassEnabled = true
        googleMap?.let {
            setupCluster(googleMap!!)
        }
        googleMap?.setOnMapClickListener {
            if (isClient) {
                viewModel.setType(MapNewTwoViewModel.OrderType.MY)
            } else
                viewModel.setType(MapNewTwoViewModel.OrderType.ALL)

        }
    }

setupCluster

private fun setupCluster(map: GoogleMap) {
        clusterManager = ClusterManager(MyApplication.applicationContext(), map)

        renderer = DotRenderer()
        clusterManager?.renderer = renderer
        if(clusterManager != null){
            Log.d("ClusterManager", "true")
        } else {
            Log.d("ClusterManager", "false")
        }
        map.setOnCameraIdleListener(clusterManager)
        map.setOnMarkerClickListener(clusterManager)
        map.setOnInfoWindowClickListener(clusterManager)


        clusterManager?.setOnClusterClickListener(this)
        clusterManager?.setOnClusterItemClickListener(this)

    }

在 setupViewModel 中我只是在看 MediatorLiveData

viewModel.mediatorLiveData.observe(viewLifecycleOwner, {
            Log.d("MediatorLiveData", it.size.toString())
            setItemsCluster(it)
        })

集群所需的setItemsCluster

private fun setItemsCluster(orders: List<OrderX>){
        //---somesthing Operation/.
        if(clusterManager == null){
            Log.d("ClusterManager", "null")
        }
        clusterManager?.addItems(itemClusters)
        clusterManager?.cluster()
    }

现在记录：

2020-10-21 18:53:23.658 30104-30104/com.app D/ClusterManager: null
2020-10-21 18:53:23.722 30104-30104/com.app D/ClusterManager: true
2020-10-21 18:53:23.734 30104-30104/com.app D/OnClustersChanged: []

问题，为什么viewModel.observe() 比 onMapReady 工作得更快？

毕竟我调用的比setupMap晚（onMapReady，初始化Cluster的地方）

如何解决？ 为此，我没有给ClusterManager加分

Answer 1

准备好后为地图设置绑定。像这样：

override fun onMapReady(map: GoogleMap?) {
    ...

    setupMapBindings()
}

fun setupMapBindings() {
    viewModel.mediatorLiveData.observe(viewLifecycleOwner, {
        setItemsCluster(it)
    })
}

Answer 2

getMapAsync 是异步的（顾名思义）并且地图准备好需要一些时间，当您最初观察 LiveData 时，它将返回其当前值，以便您始终拥有一个值