Android入门教程之RecyclerView的具体使用详解 Android入门教程之RecyclerView的具

RecyclerView 的基本用法
横向滚动
RecyclerView 点击事件

RecyclerView 的基本用法和我们之前学习的控件不一样，RecyclerView 属于新增控件，所以我们需要在项目的 build.gradle 中添加 RecyclerView 库的依赖，才能使用该控件

dependencies {implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"implementation 'androidx.core:core-ktx:1.2.0'implementation 'androidx.appcompat:appcompat:1.1.0'implementation 'com.google.android.material:material:1.1.0'implementation 'androidx.constraintlayout:constraintlayout:1.1.3'implementation 'androidx.recyclerview:recyclerview:1.1.0'testImplementation 'junit:junit:4.+'androidTestImplementation 'androidx.test.ext:junit:1.1.1'androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'}

修改 activity_main.xml 中的代码，如下所示

这里我们想要使用 RecyclerView 实现了 ListView 一样的效果，准备一个适配器，新建 FruitAdapter 类，让这个适配器继承 RecyclerView.Adapter，并将泛型指定为 FruitAdapter.ViewHolder，其中 ViewHolder 是我们在 FruitAdapter 中定义的一个内部类

class FruitAdapter(val fruitList: List) : RecyclerView.Adapter() {inner class ViewHolder(view: View) : RecyclerView.ViewHolder(view) {val fruitImage: ImageView = view.findViewById(R.id.fruitImage)val fruitName: TextView = view.findViewById(R.id.fruitName)}override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): FruitAdapter.ViewHolder {val view = LayoutInflater.from(parent.context).inflate(R.layout.fruit_item, parent, false)return ViewHolder(view)}override fun getItemCount() = fruitList.sizeoverride fun onBindViewHolder(holder: FruitAdapter.ViewHolder, position: Int) {val fruit = fruitList[position]holder.fruitImage.setImageResource(fruit.imageId)holder.fruitName.text = fruit.name}}

首先，我们定义一个内部类 ViewHolder，继承自 RecyclerView.ViewHolder，然后 ViewHolder 的主构造函数中传入一个 View 参数，这个参数通常是 RecyclerView 子项的最外层布局，然后我们就可以通过 findViewById() 方法来获取布局中的 ImageView 和 TextView 实例了
FruitAdapter 继承自 RecyclerView.Adapter，那么就必须重写 onCreateViewHolder()、onBindViewHolder()、getItemCount() 这三个方法：

onCreateViewHolder() 方法用于创建 ViewHolder 实例
onBindViewHolder() 方法用于对 RecyclerView 子项的数据进行赋值
getItemCount() 方法告诉 RecyclerView 一共有多少个子项，直接返回数据源的长度

修改 MainActivity 中的代码，开始使用 RecyclerView

class MainActivity : AppCompatActivity() {private val fruitList = ArrayList()override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)setContentView(R.layout.activity_main)initFruits()val layoutManager = LinearLayoutManager(this)recyclerView.layoutManager = layoutManagerval adapter = FruitAdapter(fruitList)recyclerView.adapter = adapter}private fun initFruits() {repeat(2) {fruitList.add(Fruit("Apple", R.drawable.apple_pic))fruitList.add(Fruit("Banana", R.drawable.banana_pic))fruitList.add(Fruit("Orange", R.drawable.orange_pic))fruitList.add(Fruit("Watermelon", R.drawable.watermelon_pic))fruitList.add(Fruit("Pear", R.drawable.pear_pic))fruitList.add(Fruit("Grape", R.drawable.grape_pic))fruitList.add(Fruit("Pineapple", R.drawable.pineapple_pic))fruitList.add(Fruit("Strawberry", R.drawable.strawberry_pic))fruitList.add(Fruit("Cherry", R.drawable.cherry_pic))fruitList.add(Fruit("Mango", R.drawable.mango_pic))}}}

在 onCreate() 方法中先创建一个 LinearLayoutManager 对象，并设置到 RecyclerView 中，用于指定 RecyclerView 的布局方式。然后再创建 FruitAdapter 的实例，调用 RecyclerView 的 setAdapter() 方法完成适配器设置

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横向滚动如果我们要实现横向滚动的话，要先对 fruit_item 的布局进行修改，把里面的元素改成垂直排列

接下来修改 MainActivity 中的代码

class MainActivity : AppCompatActivity() {private val fruitList = ArrayList()override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)setContentView(R.layout.activity_main)initFruits()val layoutManager = LinearLayoutManager(this)layoutManager.orientation = LinearLayoutManager.HORIZONTALrecyclerView.layoutManager = layoutManagerval adapter = FruitAdapter(fruitList)recyclerView.adapter = adapter} ...}

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除了横向滚动，RecyclerView 还能实现瀑布流和网格布局

RecyclerView 点击事件不同于 ListView，RecyclerView 并没有提供类似于 setOnItemClickListener() 这样的注册监听器方法，而是需要我们自己给子项具体的 View 注册点击事件
修改 FruitAdapter 中的代码

class FruitAdapter(val fruitList: List) : RecyclerView.Adapter() {inner class ViewHolder(view: View) : RecyclerView.ViewHolder(view) {val fruitImage: ImageView = view.findViewById(R.id.fruitImage)val fruitName: TextView = view.findViewById(R.id.fruitName)}override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): FruitAdapter.ViewHolder {val view = LayoutInflater.from(parent.context).inflate(R.layout.fruit_item, parent, false)val viewHolder = ViewHolder(view)viewHolder.itemView.setOnClickListener {val position = viewHolder.adapterPositionLog.d("FruitAdapter", position.toString())val fruit = fruitList[position]Toast.makeText(parent.context, "you clicked view ${fruit.name}", Toast.LENGTH_SHORT).show()}viewHolder.fruitImage.setOnClickListener {val position = viewHolder.adapterPositionLog.d("FruitAdapter", position.toString())val fruit = fruitList[position]Toast.makeText(parent.context, "you clicked image ${fruit.name}", Toast.LENGTH_SHORT).show()}return viewHolder}override fun getItemCount() = fruitList.sizeoverride fun onBindViewHolder(holder: FruitAdapter.ViewHolder, position: Int) {val fruit = fruitList[position]holder.fruitImage.setImageResource(fruit.imageId)holder.fruitName.text = fruit.name}}

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