未解决的参考：onBindViewHolder 内的 LAYOUT_INFLATER_SERVICE

Question

在我的RecyclerView Adapter 的OnBindViewHolder 内，我有多个项目。其中一个（ITEM_TRATAMENTOS）有一个 setOnClickListener，其目的是在我单击一个按钮（add_field_btn）时创建一个LinearLayout。问题是getSystemService 的唯一参数未解决（Context.LAYOUT_INFLATER_SERVICE）。

在ViewPagers 中它工作正常，但在 OnBindViewHolder 中，情况并非如此。

 ITEM_TRATAMENTOS ->{
      val viewHolderTratamentos = holder as ViewHolderItemTratamentos
      holder.add_field_btn.setOnClickListener {
                    inflater = Context.getSystemService(Context.LAYOUT_INFLATER_SERVICE) as LayoutInflater
                    val rowView = inflater.inflate(R.layout.used_products_field, null)
                    // Add the new row.
                    parentLinearLayout?.addView(rowView, parentLinearLayout?.childCount!! - 1)
            }
  }

预期的结果是创建新行，如果它在正常活动中，它将起作用。

Answer 1

另一种解决方案是从parentLinearLayout ViewGroup 获取LayoutInflater。

示例

parentLinearLayout?.apply { 
    val inflater = LayoutInflater.from(context) // context is now available in the receiver scope
    val rowView = inflater.inflate(R.layout.used_products_field, this, false)
    addView(rowView) // Add the view to the last position
}

另外，请注意添加过多视图而不回收它们的后果。如果数量足够大，您可能还需要另一个 RecyclerView。

Answer 2

第 1 步：将 LayoutInflater 参数添加到 RecyclerView.Adapter 子类的构造函数中。

第 2 步：创建RecyclerView.Adapter 时，传入一个LayoutInflater，该LayoutInflater 是从您的活动的getLayoutInflater() 获得的。

例如，这里有一个名为ColorAdapter的RecyclerView.Adapter：

/*
  Copyright (c) 2018 CommonsWare, LLC

  Licensed under the Apache License, Version 2.0 (the "License"); you may not
  use this file except in compliance with the License. You may obtain   a copy
  of the License at http://www.apache.org/licenses/LICENSE-2.0. Unless required
  by applicable law or agreed to in writing, software distributed under the
  License is distributed on an "AS IS" BASIS,   WITHOUT WARRANTIES OR CONDITIONS
  OF ANY KIND, either express or implied. See the License for the specific
  language governing permissions and limitations under the License.

  Covered in detail in the book _Elements of Android Jetpack_

  https://commonsware.com/Jetpack
*/

package com.commonsware.jetpack.sampler.recyclerview

import android.view.LayoutInflater
import android.view.ViewGroup
import androidx.recyclerview.widget.DiffUtil
import androidx.recyclerview.widget.ListAdapter

class ColorAdapter(private val inflater: LayoutInflater) :
  ListAdapter<Int, ColorViewHolder>(ColorDiffer) {

  override fun onCreateViewHolder(
    parent: ViewGroup,
    viewType: Int
  ): ColorViewHolder {
    return ColorViewHolder(inflater.inflate(R.layout.row, parent, false))
  }

  override fun onBindViewHolder(holder: ColorViewHolder, position: Int) {
    holder.bindTo(getItem(position))
  }

  private object ColorDiffer : DiffUtil.ItemCallback<Int>() {
    override fun areItemsTheSame(oldColor: Int, newColor: Int): Boolean {
      return oldColor == newColor
    }

    override fun areContentsTheSame(oldColor: Int, newColor: Int): Boolean {
      return areItemsTheSame(oldColor, newColor)
    }
  }
}

请注意，我的 ColorAdapter 构造函数有 private val inflater: LayoutInflater 作为参数。

这是使用 ColorAdapter 的活动：

/*
  Copyright (c) 2018 CommonsWare, LLC

  Licensed under the Apache License, Version 2.0 (the "License"); you may not
  use this file except in compliance with the License. You may obtain   a copy
  of the License at http://www.apache.org/licenses/LICENSE-2.0. Unless required
  by applicable law or agreed to in writing, software distributed under the
  License is distributed on an "AS IS" BASIS,   WITHOUT WARRANTIES OR CONDITIONS
  OF ANY KIND, either express or implied. See the License for the specific
  language governing permissions and limitations under the License.

  Covered in detail in the book _Elements of Android Jetpack_

  https://commonsware.com/Jetpack
*/

package com.commonsware.jetpack.sampler.recyclerview

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.recyclerview.widget.DividerItemDecoration
import androidx.recyclerview.widget.LinearLayoutManager
import kotlinx.android.synthetic.main.activity_main.*
import java.util.*

class MainActivity : AppCompatActivity() {
  private val random = Random()

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    items.apply {
      layoutManager = LinearLayoutManager(this@MainActivity)
      addItemDecoration(
        DividerItemDecoration(this@MainActivity, DividerItemDecoration.HORIZONTAL)
      )
      adapter = ColorAdapter(layoutInflater).apply {
        submitList(buildItems())
      }
    }
  }

  private fun buildItems() = generateSequence { random.nextInt() }
    .take(25)
    .toList()
}

由于您和我都使用 Kotlin 编写代码，因此 getLayoutInflater() 调用会变成对活动上 layoutInflater 属性的引用。所以，当我创建ColorAdapter 时，我使用ColorAdapter(layoutInflater) 来传递LayoutInflater 的实例。