Android入門教程之RecyclerView的具體使用詳解

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RecyclerView 的基本用法

和我們之前學習的控件不一樣，RecyclerView 屬於新增控件，所以我們需要在項目的 build.gradle 中添加 RecyclerView 庫的依賴，才能使用該控件

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 中的代碼，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>

這裡我們想要使用 RecyclerView 實現瞭 ListView 一樣的效果，準備一個適配器，新建 FruitAdapter 類，讓這個適配器繼承 RecyclerView.Adapter，並將泛型指定為 FruitAdapter.ViewHolder，其中 ViewHolder 是我們在 FruitAdapter 中定義的一個內部類

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，我們定義一個內部類 ViewHolder，繼承自 RecyclerView.ViewHolder，然後 ViewHolder 的主構造函數中傳入一個 View 參數，這個參數通常是 RecyclerView 子項的最外層佈局，然後我們就可以通過 findViewById() 方法來獲取佈局中的 ImageView 和 TextView 實例瞭

FruitAdapter 繼承自 RecyclerView.Adapter，那麼就必須重寫 onCreateViewHolder()、onBindViewHolder()、getItemCount() 這三個方法：

  • onCreateViewHolder() 方法用於創建 ViewHolder 實例
  • onBindViewHolder() 方法用於對 RecyclerView 子項的數據進行賦值
  • getItemCount() 方法告訴 RecyclerView 一共有多少個子項，直接返回數據源的長度

修改 MainActivity 中的代碼，開始使用 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() 方法中先創建一個 LinearLayoutManager 對象，並設置到 RecyclerView 中，用於指定 RecyclerView 的佈局方式。然後再創建 FruitAdapter 的實例，調用 RecyclerView 的 setAdapter() 方法完成適配器設置

在這裡插入圖片描述

橫向滾動

如果我們要實現橫向滾動的話，要先對 fruit_item 的佈局進行修改，把裡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>

接下來修改 MainActivity 中的代碼

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
    }

	...
}

在這裡插入圖片描述

除瞭橫向滾動，RecyclerView 還能實現瀑佈流和網格佈局

RecyclerView 點擊事件

不同於 ListView，RecyclerView 並沒有提供類似於 setOnItemClickListener() 這樣的註冊監聽器方法，而是需要我們自己給子項具體的 View 註冊點擊事件

修改 FruitAdapter 中的代碼

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
    }
}

到此這篇關於Android入門教程之RecyclerView的具體使用詳解的文章就介紹到這瞭,更多相關Android RecyclerView內容請搜索WalkonNet以前的文章或繼續瀏覽下面的相關文章希望大傢以後多多支持WalkonNet！

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