Android学习第七天

添加RecyclerView控件

在布局中加入RecyclerView控件也是非常简单的，先为RecyclerView指定一个id，然后将宽度和高度都设
置为match_parent，这样RecyclerView就占满了整个布局的空间。
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
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>

定义实体类和子项布局

接着定义一个实体类，作为RecyclerView适配器的适配类型。

新建Fruit类，代码如下所示： class Fruit(val name:String, val imageId: Int)

定义实体类和子项布局
然后需要为RecyclerView的子项指定一个我们自定义的布局，在layout目录下新建fruit_item.xml，
代码如下所示：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="60dp">
<ImageView
android:id="@+id/fruitImage"
android:layout_width="40dp"
android:layout_height="40dp"
android:layout_gravity="center_vertical"
android:layout_marginLeft="10dp"/>
<TextView
android:id="@+id/fruitName"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:layout_marginLeft="10dp" />
</LinearLayout>

定义RecyclerView适配器

接下来需要为RecyclerView准备一个适配器，新建FruitAdapter类，让这个适配器继承自
RecyclerView.Adapter，并将泛型指定为FruitAdapter.ViewHolder。
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): ViewHolder {
val view = LayoutInflater.from(parent.context).inflate(R.layout.fruit_item, parent, false)
return ViewHolder(view)
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
val fruit = fruitList[position]
holder.fruitImage.setImageResource(fruit.imageId)
holder.fruitName.text = fruit.name
}
override fun getItemCount() = fruitList.size
}

使用RecyclerView
适配器准备好了之后，我们就可以开始使用RecyclerView了。
class MainActivity : AppCompatActivity() {
private val fruitList = ArrayList<Fruit>()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
initFruits() // 初始化水果数据
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))
}
}
}