RecycleView懶加載失效問題（二）

前言：繼《RecycleView懶加載失效問題》之后，再介紹另一個場景，如下圖，兩層RecycleView，外層是豎向串列樣式，內層是網格樣式，由于內層網格個數不固定，需要內層RecycleView的根布局高度為wrap_content（注：這是導致內層RecycleView懶加載失效的原因）

問題：盡管第2項只顯示了一小部分，但仍加載了全部資料，內層懶加載失效，當內層資料量很大，一次要全部加載，會感覺到卡頓，

分析：首先，分析為什么外層的RecycleView懶加載正常，而內層的RecycleView失效了呢？區別在于外層RecycleView高度是確定的，至少不會超過父控制元件，而內層根布局高度為wrap_content，即item沒有對最大高度做限制，內層需要多大就賦予多大，于是就加載了全部內層的資料，我們可以先將內層的根布局高度設定為固定值驗證一下，發現高度固定后內層也支持懶加載了，畢竟RecycleView高度限制了，超過高度的item就不加載了，但是這個就不滿足我們的需求了，內層資料少的時候會留白，資料多的時候顯示不全，而且只是外層回應滑動事件，內層無法回應，所有我們只能將內層根布局高度設定為wrap_content，

1、外層配接器

class TestPercentAdapter : RecyclerView.Adapter<TestPercentAdapter.TestPercentViewHolder>(){
    private val testPercentList = arrayListOf<TestPercentBean>()

    init {
        for (i in 1..20){
            testPercentList.add(TestPercentBean("外層第${i}項"))
        }
    }

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

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

    override fun onBindViewHolder(holder: TestPercentViewHolder, position: Int) {
        holder.tvItem.text = testPercentList[position].mTitle
        holder.adapterTwo.testChildrenList = testPercentList[position].mChildrenList
        holder.adapterTwo.notifyDataSetChanged()
        Log.e("aa", "***************${testPercentList[position].mTitle}")
    }


   inner class TestPercentViewHolder(view: View) : RecyclerView.ViewHolder(view) {
        val tvItem = view.findViewById<TextView>(R.id.tv_item)
        val rvItem = view.findViewById<RecyclerView>(R.id.rv_item)
        val adapterTwo = TestChildrenAdapter()
        init {
            rvItem.layoutManager = GridLayoutManager(rvItem.context, 2)
            rvItem.adapter = adapterTwo
        }
    }
}

2、外層布局

<?xml version="1.0" encoding="utf-8"?>
<com.hualala.myapplication.MyLinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <TextView
        android:id="@+id/tv_item"
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:gravity="center"
        android:textColor="@color/colorAccent"/>

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rv_item"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
</com.hualala.myapplication.MyLinearLayout>

3、內層配接器

class TestChildrenAdapter : RecyclerView.Adapter<TestChildrenAdapter.TestChildrenViewHolder>(){
    var testChildrenList = arrayListOf<TestPercentBean.TestChildrenBean>()


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

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

    override fun onBindViewHolder(holder: TestChildrenViewHolder, position: Int) {
        holder.tv_test.text = testChildrenList[position].mTitle
        Log.e("aa", "***********${testChildrenList[position].mTitle}")
    }

    class TestChildrenViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val tv_test = itemView.findViewById<TextView>(R.id.tv_test)
    }
}

4、內層布局

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/tv_test"
    android:layout_width="match_parent"
    android:layout_height="40dp"
    android:gravity="center"
    android:textColor="@color/colorPrimaryDark"/>

5、主頁布局

<?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"/>
    <View
        android:layout_width="1px"
        android:layout_height="match_parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:background="#666666"/>
    <Button
        android:id="@+id/bt_update"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toEndOf="@+id/rv_test"
        android:layout_marginStart="10dp"
        android:layout_marginRight="10dp"
        app:layout_constraintEnd_toEndOf="parent"
        android:gravity="center"
        android:text="更新"/>
</androidx.constraintlayout.widget.ConstraintLayout>

6、加載資料

rv_test.layoutManager = LinearLayoutManager(this)
        rv_test.adapter = TestPercentAdapter()
        bt_update.setOnClickListener { (rv_test.adapter as TestPercentAdapter).notifyDataSetChanged() }

8、物體類

class TestPercentBean constructor(title: String){
    val mTitle = title
    val mChildrenList = ArrayList<TestChildrenBean>()
    init {
        for (i in 1..(Math.random() * 100).toInt()){
            mChildrenList.add(TestChildrenBean("內層第{$i}項"))
        }
    }
    
    class TestChildrenBean constructor(title: String){
        val mTitle = title
    }
}

方案：分析了原因，有了初步的方案，需要滿足這兩個條件即可解決：1、給內部RecycleView設定最大高度為外層RecycleView高度（解決懶加載，最多加載條數進行了限制，不會無限大） 2、滑動沖突（這部分太過于復雜，導致最終放棄了該方案，可以想一下我點擊在第一項內層的RecycleView上向上滑動，由于已經都顯示了無需再加載了需要把事件交給外層RecycleView，但當第2項內層RecycleView全部顯示出來時，又要將事件給第2項內層RecycleView繼續加載剩下的資料，全部顯示后再將事件交給外層RecycleView——即內層RecycleView布局未全部顯示出來時外層回應滑動，全部顯示則內層回應，如果內層滑動到第1item或最后item，則再由外層回應）

簡單方案：考慮上面的方案復雜，那就換一種思路，用單層RecycleView實作，則需要網格支持動態分配列數，當為外層資料時為1列，為內層資料時為2列，

通過GridLayoutManager.SpanSizeLookup實作動態列數

1、GridLayoutManager第2個引數spanCount為每行列數的最小公倍數
2、getSpanSize回傳值為spanCount除以該行列數

1、配接器

class TestAdapter : RecyclerView.Adapter<TestAdapter.TestViewHolder>() {

    var testList = ArrayList<TestBean>()

    init {
        for (i in 1..20) {
            testList.add(TestBean("外層第${i}項", true))
            for (j in 1..(Math.random() * 100).toInt()) {
                testList.add(TestBean("內層第${j}項", false))
            }
        }
    }

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

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

    override fun onBindViewHolder(holder: TestViewHolder, position: Int) {
        holder.tv_test.text = testList[position].mTitle
        if (testList[position].mIsPercent){
            holder.tv_test.setTextColor(holder.tv_test.resources.getColor(R.color.colorAccent))
        }else{
            holder.tv_test.setTextColor(holder.tv_test.resources.getColor(R.color.colorPrimaryDark))
        }
        Log.e("aa", "***********${testList[position].mTitle}")
    }

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

2、子項布局

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/tv_test"
    android:layout_width="match_parent"
    android:layout_height="40dp"
    android:gravity="center"
    android:textColor="@color/colorPrimaryDark"/>

3、物體類

class TestBean(title: String, isPercent: Boolean) {
    val mTitle = title
    val mIsPercent = isPercent
}

4、加載資料

/* 1、GridLayoutManager第2個引數spanCount為每行列數的最小公倍數
 * 2、getSpanSize回傳值為spanCount除以該行列數
 * */
val gridLayoutManager = GridLayoutManager(this, 2)
        val testAdapter = TestAdapter()
        gridLayoutManager.spanSizeLookup = object : GridLayoutManager.SpanSizeLookup(){
            override fun getSpanSize(position: Int): Int {
                return if (testAdapter.testList[position].mIsPercent) 2 else 1
            }
        }
        rv_test.layoutManager = gridLayoutManager
        rv_test.adapter = testAdapter
        bt_update.setOnClickListener { (rv_test.adapter as TestAdapter).notifyDataSetChanged() }