简要介绍

本demo按照MVVM方式实现最简单的数据展示(支持自动分页加载)和删除的demo,用于展示一个完整的MVVM架构.

1. 包含:ViewModel+LiveData+Room+Paging
2. 语言:Kotlin
3. 采用kotlin coroutines实现数据库操作
4. 包含databinding

代码实现(只贴出重点代码,完整代码见源代码)

1. UserActivity

class UserActivity : AppCompatActivity() {
    private lateinit var viewModel: UserViewModel
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val binding: ActivityUserBinding = DataBindingUtil.setContentView(this, R.layout.activity_user)
        val factory = InjectorUtils.provideUserViewModelFactory(this)
        viewModel = ViewModelProviders.of(this, factory).get(UserViewModel::class.java)
        val adapter = UserAdapter()
        adapter.listener = View.OnClickListener { view ->
            view?.let {
                val user = view.tag as User
                viewModel.delUser(user.id)
            }
        }

        binding.userRv.adapter = adapter
        viewModel.userList.observe(this, Observer { adapter.submitList(it) })
    }
}

2. UserAdapter

class UserAdapter : PagedListAdapter<User, UserAdapter.ViewHolder>(UserDiffCallback()) {
    lateinit var listener: View.OnClickListener
    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        val data = getItem(position) ?: return
        holder.apply {
            bind(listener, data)
            itemView.tag = data
        }
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        return ViewHolder(ItemUserBinding.inflate(
                LayoutInflater.from(parent.context), parent, false))
    }

    class ViewHolder(
            private val binding: ItemUserBinding
    ) : RecyclerView.ViewHolder(binding.root) {
        fun bind(listener: View.OnClickListener, item: User) {
            binding.apply {
                clickListener = listener
                user = item
                executePendingBindings()
            }
        }
    }
}

private class UserDiffCallback : DiffUtil.ItemCallback<User>() {
    override fun areContentsTheSame(oldItem: User, newItem: User): Boolean {
        return oldItem.id == newItem.id
    }

    override fun areItemsTheSame(oldItem: User, newItem: User): Boolean {
        return oldItem == newItem
    }
}

3. UserViewModel

class UserViewModel internal constructor(private val userRepository: UserRepository) : ViewModel() {
    val userList = userRepository.getUserList()

    fun delUser(id: Int) {
        GlobalScope.launch {
            userRepository.delUser(id)
        }
    }
}

4. UserRepository

class UserRepository private constructor(private val userDao: UserDao) {

    fun getUserList() = userDao.getUserList().toLiveData(Config(
            pageSize = 30,
            enablePlaceholders = true))

    suspend fun addUser(name: String) {
        withContext(Dispatchers.IO) {
            val user = User(0, name)
            userDao.add(user)
        }
    }

    suspend fun delUser(id: Int) {
        withContext(Dispatchers.IO) {
            val user = User(id, "")
            userDao.del(user)
        }
    }

    companion object {
        @Volatile
        private var instance: UserRepository? = null

        fun getInstance(userDao: UserDao) =
                instance ?: synchronized(this) {
                    instance
                            ?: UserRepository(userDao).also { instance = it }
                }
    }
}

5. UserDao

@Dao
interface UserDao {
    @Query("SELECT * FROM User")
    fun getUserList(): DataSource.Factory<Int, User>

    @Insert
    fun add(user: User)

    @Insert
    fun add(users: List<User>)

    @Delete
    fun del(user:User)
}

Demo源代码

https://gitee.com/cxyzy1/mvvmDemo/tree/master/app_paging_databinding

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