📚 03-基本组件与布局

3.1 布局类型

• LinearLayout、RelativeLayout（旧）、ConstraintLayout（推荐）。

3.2 XML 布局示例

<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/tvHello"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

3.3 RecyclerView 列表

class MyAdapter(private val items: List<String>) : RecyclerView.Adapter<MyVH>() {
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyVH {
        val view = LayoutInflater.from(parent.context)
            .inflate(android.R.layout.simple_list_item_1, parent, false)
        return MyVH(view)
    }
    override fun onBindViewHolder(holder: MyVH, position: Int) {
        holder.text.text = items[position]
    }
    override fun getItemCount() = items.size
}

class MyVH(view: View): RecyclerView.ViewHolder(view) {
    val text: TextView = view.findViewById(android.R.id.text1)
}