1

我想观察一个 MutableList，因此当从 MutableList 添加或删除项目时，DiffUtil 将更新 RecycerView。我认为更新列表的最佳方法是使用 LiveData，但我无法在 MutableList 中添加或删除项目。

我一直在关注下面的这个代码实验室来尝试帮助我。

https://codelabs.developers.google.com/codelabs/kotlin-android-training-diffutil-databinding/#4

主要活动

class MainActivity : AppCompatActivity() {
    val list: LiveData<MutableList<User>>? = null
    var mAdapter = RVAdapter

    override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
        addUser()
        val rv = findViewById<RecyclerView>(R.id.recycler_view)
        rv.apply {
            LayoutManager = LinearLayoutManager(baseContext, LinearLayoutManager.VERTICAL, false)
            adapter = mAdapter
        }

        list?.observe(viewLifeCycleOwner, Observer {
            it?.let {
                mAdapter.submitList(it)
            }
        }
    }

    private fun addUser() {
        list.add(User("Shawn", 1)
        list.add(User("Shannon", 2)
        list.add(User("Steve", 3)
        list.add(User("Sara", 4)

    } 
}

用户数据类

data class User(val name: String, val accountNumber: Int) {
}

适配器

class RVAdapter : ListAdapter<User, RVAdapter.ViewHolder>(MyDiffCallback()) {

    class MyDiffCallback : DiffUtil.ItemCallback<User>() {
        override fun areItemsTheSame(oldItem: User, newItem: User): Boolean {
            return oldItem.name == newItem.name
        }

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

   ... 
}

这是我目前的代码，我无法从列表中添加或删除项目，并且 ViewLifecycleOwner 未定义。

4

2 回答 2

0

可能这会有所帮助。你可以实现你想要的，但你总是必须将 LiveData 与 ViewModel 结合起来以获取数据并更新它。谷歌建议这样做。

class MainActivity : AppCompatActivity() {
    val list: LiveData<MutableList<User>> = MutableLiveData<List<User>>().apply{
       postValue(mutableListOf<User>())
    }
    var mAdapter = RVAdapter

    override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
        addUser()
        val rv = findViewById<RecyclerView>(R.id.recycler_view)
        rv.apply {
            LayoutManager = LinearLayoutManager(baseContext, LinearLayoutManager.VERTICAL, false)
            adapter = mAdapter
        }

        list?.observe(viewLifeCycleOwner, Observer {
            it?.let {
                mAdapter.submitList(it)
            }
        }
    }

    private fun addUser() {
        
        val userList = list.getValue()
        userList .add(User("Shawn", 1)
        userList .add(User("Shannon", 2)
        userList .add(User("Steve", 3)
        userList .add(User("Sara", 4)
        list.postValue(userList)

    } 

    private fun editUser() {
       val userList = list.getValue()
        userList.add(User("Shawn", 21)
        
        list.postValue(userList)
    }
}
于 2020-10-05T15:41:44.100 回答
0

首先，您需要初始化您的 livedata 并将您的列表发布到它。您可以查看以下示例

class MainActivity : AppCompatActivity() {
    val list = MutableLiveData<List<User>?>()
    var mAdapter = RVAdapter

    override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
        addUser()
        val rv = findViewById<RecyclerView>(R.id.recycler_view)
        rv.apply {
            LayoutManager = LinearLayoutManager(baseContext, LinearLayoutManager.VERTICAL, false)
            adapter = mAdapter
        }

        list.observe(this, Observer {
            it?.let {
                mAdapter.submitList(it)
            }
        }
    }

    private fun addUser() {
        val newList = mutableListOf<User>()
        newList.add(User("Shawn", 1)
        newList.add(User("Shannon", 2)
        newList.add(User("Steve", 3)
        newList.add(User("Sara", 4)
        list.postValue(newList)
    } 
}
于 2020-10-05T14:58:03.197 回答