向后按下时碎片会被破坏。 我希望它在后退时不会被破坏，这样我就可以保存片段的状态

Question

我创建了一个 Activity 并向其中添加了 3 个片段。 第一个是 HomeFragment，第二个是 ProductDetailFragment，第三个是 CartFragment。 我已经从 ProductDetailFragment 添加了多个产品数量，并且我希望保存数量详细信息，即使我返回到 HomeFragment 并再次返回到 ProductDetailFragment。 但是，一旦我按回 go 到 HomeFragment，ProductDetailFragment 就会被销毁，如果再次回到 ProductDetailFragment，数量值就会全部消失。

我试过 onSaveInstanceState 来存储 state 即使片段被破坏但在这种情况下不起作用。 让我告诉你我的代码：

产品细节片段

lateinit var binding: FragmentProductDetailBinding
    var quantityValue = 0

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        Toast.makeText(activity,"onCreateCalled",Toast.LENGTH_SHORT).show()
        if(savedInstanceState == null) {
            quantityValue = 0
        } else {
            quantityValue = savedInstanceState.getInt("quantity",0)
        }

override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
       /// return inflater.inflate(R.layout.fragment_product_detail, container, false)


        binding = FragmentProductDetailBinding.inflate(inflater,container,false)
        binding.productDetails1 = arguments?.getParcelable("product")
        var productDetail = binding.productDetails1

       // var priceAmount = binding.priceAmount.text.toString().toFloat()

        Log.d("PriceAmount", binding.priceAmount.text.toString())

       // Log.d("ProductTitle", binding.productDetails1.title)
                binding.addButton.setOnClickListener {
                // Log.d("ProductDetail",initialValue.toString())
                if (productDetail == null) return@setOnClickListener
                quantityValue = quantityValue + 1
                binding.totalPriceText.text = "Total price"
                binding.quantityText.text = quantityValue.toString()
                binding.priceAmount.text = (productDetail.price * quantityValue).toString()


                // Log.d("ProductDetail",priceAmount.toString())
            }
            binding.removeButton.setOnClickListener {
                if (quantityValue != 0) {
                    if (productDetail == null) return@setOnClickListener
                    quantityValue = quantityValue - 1
                    binding.quantityText.text = quantityValue.toString()
                    //   binding.priceAmount.text = (priceAmount*quantityValue).toString()
                    binding.priceAmount.text = (productDetail.price * quantityValue).toString()

                }
            }

            binding.addCartButton.setOnClickListener{
            val bundle = Bundle()
            bundle.putString("quantity_text", String.format("%d",quantityValue))
            val cartFragment = CartFragment()
                cartFragment.arguments = bundle


            val ft = fragmentManager?.beginTransaction()
            ft?.replace(R.id.flFragment,cartFragment)
            ft?.addToBackStack("")
            ft?.commit()
            // Create the transaction
            // Create the transaction
        }
        Toast.makeText(activity,"onCreateViewCalled",Toast.LENGTH_SHORT).show()

        return binding.root
    }

  override fun onSaveInstanceState(outState: Bundle) {
        super.onSaveInstanceState(outState)
        outState.putInt("quantity", quantityValue)

    }

主页片段

class HomeFragment : Fragment() {

    lateinit var binding: FragmentHomeBinding
    private val viewModel: HomeFragmentViewModel by lazy {
        ViewModelProvider(this).get(HomeFragmentViewModel::class.java)

    }



    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        binding = FragmentHomeBinding.inflate(inflater,container,false)
        return binding.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        binding.viewModel = viewModel
        binding.lifecycleOwner = viewLifecycleOwner

        val clickListener = object: ClickListener{
            override fun onClick(itemProduct: ProductDataModel) {
                val productDetailFragment = ProductDetailFragment().apply {
                    arguments = bundleOf(Pair("product",itemProduct))
                }
                val ft : FragmentTransaction = fragmentManager!!.beginTransaction()
                ft.replace(R.id.flFragment, productDetailFragment,"PRODUCT_DETAIL_FRAGMENT")
                ft.addToBackStack(null)
                ft.commit()
            }

        }

        viewModel.products.observe(viewLifecycleOwner){
            if (it.size>0){
                //Log.d("HomeFragment",it.get(0).title)
                //Log.d("HomeFragment", it.get(0).image)
                binding.productRecyclerView.adapter = ProductListAdapter(it,clickListener)
            }
        }
    }

    override fun onResume() {
        super.onResume()
        (activity as AppCompatActivity?)!!.supportActionBar!!.hide()

    }

    override fun onStop() {
        super.onStop()
        (activity as AppCompatActivity?)!!.supportActionBar!!.show()
    }

    override fun onDestroy() {
        super.onDestroy()
        Toast.makeText(activity,"onDestroyHomeFrag",Toast.LENGTH_SHORT).show()
    }

}

MainActivity ( In which all fragments are there )

class MainActivity : AppCompatActivity() {
private val viewModel:MainViewModel by viewModels()
`enter code here`var productDetailFragment = ProductDetailFragment()

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    installSplashScreen().apply {
        setKeepOnScreenCondition{
            viewModel.isLoading.value
        }

    }
    setContentView(R.layout.activity_main)
    val homeFragment = HomeFragment()

    //Starting the fragment transaction from SupportFragmentManager class
    val ft : FragmentTransaction = supportFragmentManager.beginTransaction()
    ft.add(R.id.flFragment, homeFragment,"HOME_FRAGMENT")
    ft.addToBackStack(null)
    ft.commit()

enter code here } }

Answer 1

您可以使用SharedViewModel ，因为两个片段共享相同的活动。 您可以添加要保留的数据，当您 go 到详细页面视图时 model 仍然有您想要的数据，因为它取决于活动的生命周期。

官方文档： https://developer.android.com/topic/libraries/architecture/viewmodel#sharing