从firebase数据库获取数据到android应用程序时使用进度条

Question

我想在屏幕上显示进度条，直到从 firebase 数据库中获取所有必需的数据。

如何在 fetchMenu() [in MenuFragment.kt] 中使用以下代码

.addOnSuccessListener(OnSuccessListener<Void?> { // Write was successful!
            // ...
            progressBar.visibility = View.GONE
        })
        .addOnFailureListener(OnFailureListener { // Write failed
            // ...
            progressBar.visibility = View.GONE
        })

MenuFragment.kt

class MenuFragment : Fragment() {

private var dishList: MutableList<DishModel> = mutableListOf()
private lateinit var myRef: DatabaseReference
lateinit var list: RecyclerView
lateinit var proceedToCartLayout: RelativeLayout
lateinit var addToCartBtn: Button
private var selectedCategory = ""
lateinit var progressLayout: RelativeLayout
lateinit var progressBar: ProgressBar

companion object {
    fun newInstance(): Fragment {
        return MenuFragment()
    }
}

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    val view = inflater.inflate(R.layout.fragment_menu, container, false)
    //retrieve id
    val bundle = this.arguments
    selectedCategory = bundle!!.getString("CATEGORY_ID")!!
    list = view.findViewById(R.id.recyclerMenu)
    myRef = FirebaseDatabase.getInstance().getReference("Category")
    proceedToCartLayout = view.findViewById(R.id.ProceedToCart)
    addToCartBtn = view.findViewById(R.id.btn_cart)
    progressLayout = view.findViewById(R.id.progressLayout)
    progressBar = view.findViewById(R.id.progressBar)


    return view
}


override fun onResume() {

    if (ConnectionManager().checkConnectivity(activity as Context)) {
        fetchMenu()

    } else {

        val alterDialog = androidx.appcompat.app.AlertDialog.Builder(activity as 
Context)
        alterDialog.setTitle("No Internet")
        alterDialog.setMessage("Connect to internet to continue")
        alterDialog.setIcon(R.drawable.nointernet)
        alterDialog.setPositiveButton("Open Settings") { _, _ ->
            val settingsIntent = Intent(Settings.ACTION_SETTINGS)//open wifi settings
            startActivity(settingsIntent)
        }

        alterDialog.setNegativeButton("Exit") { _, _ ->
            ActivityCompat.finishAffinity(activity as Activity)
        }
        alterDialog.setCancelable(false)

        alterDialog.create()
        alterDialog.show()

    }

    super.onResume()
}

private fun fetchMenu() {


    progressLayout.visibility = View.VISIBLE

    myRef.child(selectedCategory)
        .addValueEventListener(object : ValueEventListener {
            override fun onCancelled(p0: DatabaseError) {
                progressLayout.visibility = View.GONE
                Toast.makeText(context, "$p0", Toast.LENGTH_SHORT).show()
            }


            override fun onDataChange(p0: DataSnapshot) {
                progressLayout.visibility = View.GONE
                if (p0.exists()) {
                    dishList.clear()
                    for (i in p0.children) {
                        val plan = i.getValue(DishModel::class.java)
                        dishList.add(plan!!)
                    }

                    val adapter = MenuAdapter(
                        context!!,
                        R.layout.menu_list_item,
                        dishList,
                        proceedToCartLayout,
                        addToCartBtn, selectedCategory
                    )
                    list.adapter = adapter

                }
            }


        })
}


}

我在使用进度条后得到了结果，但没有得到所需的结果，因为我想显示进度条，直到 RecyclerView 的所有行都被从 firebase 数据库获取的数据填充并且所有视图都正确放置.

我在使用进度条时得到了这个

see the video

Answer 1

根据您共享的图像，您根本没有显示“ProgressBar”。要解决此问题，请取消注释以下代码行：

progressLayout.visibility = View.VISIBLE

并添加以下行：

progressLayout.visibility = View.GONE

在“onDataChange()”方法中也是如此。通过这种方式，当调用“fetchMenu()”方法时，您将开始显示 ProgressBar，一旦您收到响应，您可以隐藏数据或异常。