Android入门教程之RecyclerView的具体使用详解

目录

• 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

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>

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<Fruit>) : RecyclerView.Adapter<FruitAdapter.ViewHolder>() {

    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.size

    override 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<Fruit>()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        initFruits()
        val layoutManager = LinearLayoutManager(this)
        recyclerView.layoutManager = layoutManager
        val 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

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

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="80dp"
    android:layout_height="wrap_content"
    tools:ignore="UseCompoundDrawables">

    <ImageView
        android:id="@+id/fruitImage"
        android:layout_width="40dp"
        android:layout_height="40dp"
        android:layout_gravity="center_vertical"
        android:layout_marginLeft="10dp"
        tools:ignore="ContentDescription,RtlHardcoded" />

    <TextView
        android:id="@+id/fruitName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:layout_marginLeft="10dp"
        tools:ignore="RtlHardcoded" />

</LinearLayout>

接下来修改 MainActivity 中的代码

class MainActivity : AppCompatActivity() {

    private val fruitList = ArrayList<Fruit>()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        initFruits()
        val layoutManager = LinearLayoutManager(this)
        layoutManager.orientation = LinearLayoutManager.HORIZONTAL
        recyclerView.layoutManager = layoutManager
        val adapter = FruitAdapter(fruitList)
        recyclerView.adapter = adapter
    }

	...
}

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<Fruit>) : RecyclerView.Adapter<FruitAdapter.ViewHolder>() {

    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.adapterPosition
            Log.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.adapterPosition
            Log.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.size

    override 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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