Chapter 12 - Challenge: Efficient RecyclerView Reloading (SOLUTION)

Android Programming (4th Edition) 12. Fragment Navigation
1

Hi :wave:.This code is dedicated to everyone who stuck on this task :upside_down_face: . Please rate my solution :face_with_monocle:

package com.bignerdranch.android.criminalintent

import android.content.Context
import android.os.Bundle
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import android.widget.TextView
import androidx.fragment.app.Fragment
import androidx.lifecycle.ViewModelProvider
import androidx.recyclerview.widget.DiffUtil
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.ListAdapter
import androidx.recyclerview.widget.RecyclerView
import java.util.*

private const val TAG = "CrimeListFragment"

class CrimeListFragment : Fragment() {
    interface Callbacks {
        fun onCrimeSelected(crimeId: UUID)
    }

    private var callbacks: Callbacks? = null
    private lateinit var crimeRecyclerView: RecyclerView
    private var adapter: CrimeAdapter? = CrimeAdapter()
    private val crimeListViewModel: CrimeListViewModel by lazy {
        ViewModelProvider(this).get(CrimeListViewModel::class.java)

    }

    override fun onAttach(context: Context) {
        Log.i(TAG, "onAttach")
        super.onAttach(context)
        callbacks = context as Callbacks?
    }

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        Log.i(TAG, "onCreate")
        val view = inflater.inflate(R.layout.fragment_crime_list, container, false)
        crimeRecyclerView =
            view.findViewById(R.id.crime_recycler_view) as RecyclerView
        crimeRecyclerView.layoutManager = LinearLayoutManager(context)
        crimeRecyclerView.adapter = adapter
        return view
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        Log.i(TAG, "onViewCreated")
        crimeListViewModel.crimeListLiveData.observe(
            viewLifecycleOwner,
            { crimes ->
                crimes?.let {
                    Log.i(TAG, "Got crimes it ${it.size}")
                    updateUI(it)
                }
            })
    }

    private fun updateUI(crimes: List<Crime>) {
        adapter?.submitList(crimes)
    }


    private inner class CrimeHolder(view: View) : RecyclerView.ViewHolder(view),
        View.OnClickListener {

        private lateinit var crime: Crime

        private val titleTextView: TextView = itemView.findViewById(R.id.crime_title)
        private val dateTextView: TextView = itemView.findViewById(R.id.crime_date)
        private val solvedImageView: ImageView = itemView.findViewById(R.id.crime_solved)

        init {
            itemView.setOnClickListener(this)
        }

        fun bind(crime: Crime) {
            this.crime = crime
            titleTextView.text = this.crime.title
            dateTextView.text = this.crime.date.toString()
            solvedImageView.visibility = if (crime.isSolved) {
                View.VISIBLE
            } else {
                View.GONE
            }
        }

        override fun onClick(v: View) {
            callbacks?.onCrimeSelected(crime.id)
        }
    }

    private inner class CrimeAdapter
        : ListAdapter<Crime, CrimeHolder>(DiffCallback) {


        override fun onCreateViewHolder(parent: ViewGroup, viewType: Int)
                : CrimeHolder {
            val view = layoutInflater.inflate(R.layout.list_item_crime, parent, false)
            return CrimeHolder(view)
        }

        override fun onBindViewHolder(holder: CrimeHolder, position: Int) {
            val crime = currentList[position]
            holder.bind(crime)
        }

        override fun getItemCount() = currentList.size
    }

    object DiffCallback : DiffUtil.ItemCallback<Crime>() {
        override fun areItemsTheSame(oldItem: Crime, newItem: Crime): Boolean {
            return oldItem.id == newItem.id
        }

        override fun areContentsTheSame(oldItem: Crime, newItem: Crime): Boolean {
            return oldItem == newItem
        }
    }


    companion object {
        fun newInstance(): CrimeListFragment {
            return CrimeListFragment()
        }
    }

    override fun onDetach() {
        super.onDetach()
        callbacks = null
    }
}
3 Likes
2

thanks for your solution.

3

i’ve tried your solution. after modifing updateUI method, i found crimeListFragment has no list to display on the screen.