kotlin: 用viewmodel展示数据
一，引入lifecycle
1,libs.versions.toml
[versions]
lifecycle = "2.9.1"
[libraries]
# lifecycle
androidx-lifecycle-livedata-core-ktx = { group = "androidx.lifecycle", name = "lifecycle-livedata-core-ktx", version.ref = "lifecycle" }
androidx-lifecycle-livedata-ktx = { group = "androidx.lifecycle", name = "lifecycle-livedata-ktx", version.ref = "lifecycle" }
androidx-lifecycle-runtime-ktx = { group = "androidx.lifecycle", name = "lifecycle-runtime-ktx", version.ref = "lifecycle" }
androidx-lifecycle-viewmodel-ktx = { group = "androidx.lifecycle", name = "lifecycle-viewmodel-ktx", version.ref = "lifecycle" }2,build.gradle.kts
dependencies {
//lifecycle
implementation(libs.androidx.lifecycle.livedata.core.ktx)
implementation(libs.androidx.lifecycle.livedata.ktx)
implementation(libs.androidx.lifecycle.runtime.ktx)
implementation(libs.androidx.lifecycle.viewmodel.ktx)
}二，UI:
fragment_user_list.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".fragment.UserListFragment">
<Button
android:id="@+id/getJsonButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:text="获取数据" />
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recycle"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"
android:background="#ffff00" />
</LinearLayout>item_oneuser_layout.xml
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/textItem"
android:layout_width="match_parent"
android:layout_height="100dp"
android:gravity="center_vertical"
android:background="#dddddd"
android:padding="16dp"
android:textSize="30sp" />三，代码
viewmodel
package com.example.okdemo2.fragment
import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel
class UserListViewModel: ViewModel() {
private val _listData = MutableLiveData<MutableList<UserListItem>>()
val listData: LiveData<MutableList<UserListItem>> = _listData
fun updateData(newData: MutableList<UserListItem>) {
_listData.value = newData
}
}model
package com.example.okdemo2.fragment
import androidx.annotation.Keep
import kotlinx.serialization.InternalSerializationApi
import kotlinx.serialization.SerialName
import kotlinx.serialization.Serializable
@Keep
@Serializable
data class UserList(
@SerialName("list")
val `list`: MutableList<UserListItem>,
@SerialName("curPage")
val curPage: Int,
@SerialName("total")
val total: Int,
@SerialName("totalPage")
val totalPage: Int,
@SerialName("token")
val token: String,
)
@Keep
@Serializable
data class UserListItem(
@SerialName("id")
val id: Int,
@SerialName("name")
val name: String,
@SerialName("image")
val image: String,
)adapter
package com.example.okdemo2.fragment
import android.view.LayoutInflater
import android.view.ViewGroup
import androidx.recyclerview.widget.DiffUtil
import androidx.recyclerview.widget.RecyclerView
import com.example.okdemo2.databinding.ItemOneuserLayoutBinding
class UserListAdapter : RecyclerView.Adapter<UserListAdapter.UserListViewHolder>(){
private var userListData: MutableList<UserListItem> = mutableListOf()
override fun onCreateViewHolder(
parent: ViewGroup,
viewType: Int
): UserListViewHolder {
//TODO("Not yet implemented")
var binding = ItemOneuserLayoutBinding.inflate(LayoutInflater.from(parent.context), parent, false)
return UserListViewHolder(binding)
}
override fun onBindViewHolder(holder: UserListViewHolder, position: Int) {
//TODO("Not yet implemented")
val item = userListData[position]
holder.bind(item)
}
override fun getItemCount(): Int {
//TODO("Not yet implemented")
return userListData.size
}
//更新数据
fun updateData(list: MutableList<UserListItem>) {
val diffResult = DiffUtil.calculateDiff(object : DiffUtil.Callback() {
override fun getOldListSize(): Int {
return userListData.size
}
override fun getNewListSize(): Int {
return list.size
}
override fun areItemsTheSame(
oldItemPosition: Int,
newItemPosition: Int
): Boolean {
var oldItem = userListData[oldItemPosition]
var newItem = list[newItemPosition]
return oldItem.id == newItem.id
}
override fun areContentsTheSame(
oldItemPosition: Int,
newItemPosition: Int
): Boolean {
var oldItem = userListData[oldItemPosition]
var newItem = list[newItemPosition]
return oldItem.id == newItem.id &&
oldItem.name == newItem.name
}
})
userListData.clear()
userListData.addAll(list)
diffResult.dispatchUpdatesTo(this)
}
// ViewHolder定义，用于绑定UI组件
class UserListViewHolder(val view: ItemOneuserLayoutBinding) : RecyclerView.ViewHolder(view.root) {
fun bind(item: UserListItem) {
view.textItem.text = item.name
}
}
}fragment
private const val ARG_PARAM1 = "param1"
private const val ARG_PARAM2 = "param2"
class UserListFragment : Fragment() {
// TODO: Rename and change types of parameters
private var param1: String? = null
private var param2: String? = null
private var _binding: FragmentUserListBinding? = null
// This property is only valid between onCreateView and
// onDestroyView.
private val binding get() = _binding!!
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
arguments?.let {
param1 = it.getString(ARG_PARAM1)
param2 = it.getString(ARG_PARAM2)
}
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
//_binding = FragmentUserListBinding.inflate(inflater, container, false)
_binding = FragmentUserListBinding.inflate(inflater, container, false)
return binding.root
}
private lateinit var viewModel: UserListViewModel //保存数据的viewmodel
private lateinit var ulAdapter: UserListAdapter //adapter
private lateinit var list: ArrayList<UserListItem> //数据
private var curPage = 0 // id,生成数据时使用
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
// 创建ViewModel实例
viewModel = ViewModelProvider(this).get(UserListViewModel::class.java)
// 创建Adapter实例
ulAdapter = UserListAdapter()
list = ArrayList<UserListItem>() // 创建可变列表
// 关联Adapter和ViewModel
viewModel.listData.observe(viewLifecycleOwner, Observer {
println("viewmodel的数据有变化...")
ulAdapter.updateData(it)
})
//绑定view和adapter
binding.recycle.layoutManager = LinearLayoutManager(context)
binding.recycle.adapter = ulAdapter
//按钮点击
binding.getJsonButton.setOnClickListener {
//创建数据
val id1 = curPage*3+1
val name1="张三"+id1
val image1 = "image"+id1
val u1 = UserListItem(id1,name1,image1)
val id2 = curPage*3+2
val name2="赵四"+id2
val image2 = "image"+id2
val u2 = UserListItem(id2,name2,image2)
val id3 = curPage*3+3
val name3="王五"+id3
val image3 = "image"+id3
val u3 = UserListItem(id3,name3,image3)
list.add(u1) // 添加元素
list.add(u2) // 添加元素
list.add(u3) // 添加元素
viewModel.updateData(list)
curPage++
}
}
override fun onDestroyView() {
super.onDestroyView()
_binding = null
}
companion object {
// TODO: Rename and change types and number of parameters
@JvmStatic
fun newInstance(param1: String, param2: String) =
UserListFragment().apply {
arguments = Bundle().apply {
putString(ARG_PARAM1, param1)
putString(ARG_PARAM2, param2)
}
}
}
}四，运行效果
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