切换片段时阻止谷歌地图重新加载

Question

在我的应用程序中，我使用DrawerLayout。当我切换到包含SupportMapFragment 的MapFragment 并返回它时，谷歌地图再次被初始化。有没有办法阻止谷歌地图这样做？我正在使用科特林。我已经阅读了关于使用 Wea​​kReference 到 MapView 的想法，但我不明白它在这种情况下有何帮助。

class MapFragment : Fragment(), OnMapReadyCallback {

    lateinit var mMap: GoogleMap

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        val view = inflater.inflate(R.layout.fragment_map, container, false)
        val mapFragment = childFragmentManager.findFragmentById((R.id.map_new)) as SupportMapFragment
        mapFragment.getMapAsync(this)
        return view
    }

    override fun onMapReady(googleMap: GoogleMap) {
        mMap = googleMap
    }


 val navigationView: NavigationView = findViewById(R.id.nav_view)
        navigationView.setNavigationItemSelectedListener {
            if(it.itemId == R.id.nav_logout){
                val intent = Intent(this, LoginActivity::class.java)
                startActivity(intent)
                true
            }
            else {
                var fragment = when (it.itemId) {
                    R.id.nav_map -> MapFragment()
                    R.id.nav_forecast -> ForecastFragment()
                    R.id.nav_app_info -> AboutFragment()
                    else -> MapFragment()
                }

                fragmentManager
                        .beginTransaction()
                        .replace(R.id.main_activity_frame, fragment)
                        .commit()
                it.isChecked = true
                drawerLayout.closeDrawers()
                true
            }
        }

Answer 1

使用以下方法可以让您在 Fragment 关闭时执行任何操作：

@Override
public void onDestroy() {
    super.onDestroy();
    //Anything you wish to do
}

@Override
public void onDetach() {
    super.onDetach();
    //Anything you wish to do
}

Answer 2

以这种方式设置您的地图，

检查它是否已经不存在 findFragmentById(R.id.map_new) 然后加载片段，否则使用已经加载的。

childFragmentManager?.run {
        findFragmentById(R.id.map)?.let {
            val mapFragment = childFragmentManager.findFragmentById(R.id.map_new)
            if (mapFragment is SupportMapFragment) {
                mapFragment.getMapAsync(this@MapFragment)
            }
        }
    }

编辑：-

这里是创建活动：-

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.act_test)

    supportFragmentManager.beginTransaction()
            .replace(R.id.fragment, MapFragment.getInstance())
            .addToBackStack("MapFragment")
            .commit()

    btnBlank.setOnClickListener {
        val frag = supportFragmentManager.findFragmentById(R.id.fragment)
        if(frag !is BlankFragment) {
            supportFragmentManager.beginTransaction()
                    .replace(R.id.fragment, BlankFragment())
                    .addToBackStack("BlankFragment")
                    .commit()
        }
    }

    btnMap.setOnClickListener {
        supportFragmentManager.popBackStack("MapFragment", 0)
    }

}

还有MapFragment：-

class MapFragment : Fragment(), OnMapReadyCallback {

private lateinit var map: GoogleMap

companion object {
    private val INSTANCE = MapFragment()
    fun getInstance() = INSTANCE
}

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? =
        inflater.inflate(R.layout.fragment_map, container, false)

override fun onActivityCreated(savedInstanceState: Bundle?) {
    super.onActivityCreated(savedInstanceState)
    childFragmentManager.run {
        findFragmentById(R.id.map)?.let {
            val mapFragment = childFragmentManager.findFragmentById(R.id.map)
            if (mapFragment is SupportMapFragment) {
                mapFragment.getMapAsync(this@MapFragment)
            }
        }
    }
}

override fun onMapReady(p0: GoogleMap?) {
    p0?.animateCamera(CameraUpdateFactory.newLatLngZoom(LatLng(
            p0.cameraPosition.target.latitude,
            p0.cameraPosition.target.longitude
    ), 14f))
}


}

Answer 3

您必须通过此代码阻止片段重新创建页面：

   mViewPager.setOffscreenPageLimit(NumberOfYourPages);