RecycleView懒加载失效问题

前言：当数据量比较大（如200条以上）明显感觉到APP卡顿，通过排查发现是RecycleView适配器的onBindViewHolder有多少条数据就执行多少次，滑动显示懒加载失效了。

原因：RecycleView或父控件在水平方向使用android:layout_weight="1"属性则会导致RecycleView懒加载无效

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal">
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rv_test"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"/>
    <LinearLayout
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"/>
</LinearLayout>

class TestAdapter : RecyclerView.Adapter<TestAdapter.TestViewHolder>(){
    private val testList = arrayListOf<String>()

    init {
        for (i in 1..500){
            testList.add("第{$i}项")
        }
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): TestViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.item_test, parent, false)
        return TestViewHolder(view)
    }

    override fun getItemCount(): Int {
        return testList.size
    }

    override fun onBindViewHolder(holder: TestViewHolder, position: Int) {
        holder.tvItem.text = testList[position]
        Log.e("aa", "***********$position")
    }


    class TestViewHolder(view: View) : RecyclerView.ViewHolder(view) {
        val tvItem = view.findViewById<TextView>(R.id.tv_item)
    }
}

rv_test.layoutManager = LinearLayoutManager(this)
rv_test.adapter = TestAdapter()

方案：对于RecycleView在水平方向需要百分比，不要采用“LinearLayout + layout_weight”方案，可以使用“ConstraintLayout+layout_constraintWidth_percent”代替

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rv_test"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintWidth_percent="0.5"/>
    <LinearLayout
        android:layout_width="0dp"
        android:layout_height="match_parent"
        app:layout_constraintStart_toEndOf="@+id/rv_test"
        app:layout_constraintEnd_toEndOf="parent"/>
</androidx.constraintlayout.widget.ConstraintLayout>

最后：还有另一种失效情况《RecycleView懒加载失效问题（二）》