Xamarin中如何获取RecyclerView屏幕外TextView的数据？

在Xamarin Android应用中，需要给RecyclerView内的可修改字段添加保存功能。尝试通过直接访问TextView收集数据，但无法获取屏幕外的TextView内容，之前用_recipieEditRecyclerView.ChildCount和FindViewHolderForAdapterPosition的方法也失败了。

核心思路是让数据源与UI双向同步：不要从RecyclerView的View中提取数据，而是在用户修改UI时实时更新对应的数据源，保存时直接读取数据源即可（RecyclerView的回收机制导致屏幕外View无法可靠访问，这是标准解决方案）。

步骤1：重构为单一数据源实体 #

把原来分散的三个List（名称、数量、单位）整合成一个实体类，方便维护和同步：

public class RecipieIngredientEditModel
{
    public int IngredientId { get; set; }
    public string Name { get; set; }
    public double Quantity { get; set; }
    public string Measurement { get; set; }
}

步骤2：修改Adapter，添加实时同步逻辑 #

更新Adapter，使用整合后的数据源，并在绑定ViewHolder时添加输入监听，实时同步用户修改到数据源：

using Android.Views;
using AndroidX.RecyclerView.Widget;
using Recipy.DataLayer;
using Recipy.Enums;
using Recipy.Models;
using Recipy.ViewHolders;
using System;
using System.Collections.Generic;
using System.IO;

namespace Recipy.Adapters
{
    internal class RecipieEditAdapter : RecyclerView.Adapter
    {
        // 对外暴露修改后的数据源
        public List<RecipieIngredientEditModel> EditIngredients { get; private set; }
        private readonly Database _database;

        public RecipieEditAdapter(int recipieId)
        {
            _database = new Database(Path.Combine(System.Environment.GetFolderPath(System.Environment.SpecialFolder.LocalApplicationData), "RecipyDataBase.db"));
            var recipieIngredients = _database.GetAllRecipieIngredients(recipieId);
            
            EditIngredients = new List<RecipieIngredientEditModel>();
            foreach (var ingredient in recipieIngredients)
            {
                EditIngredients.Add(new RecipieIngredientEditModel
                {
                    IngredientId = ingredient.IngredientId,
                    Name = _database.GetIngredientNameById(ingredient.IngredientId),
                    Quantity = _database.GetIngredientQuantityById(recipieId, ingredient.IngredientId),
                    Measurement = _database.GetIngredientMeasurementById(recipieId, ingredient.IngredientId)
                });
            }
        }

        public override int ItemCount => EditIngredients.Count;

        public override void OnBindViewHolder(RecyclerView.ViewHolder holder, int position)
        {
            if (holder is RecipieEditIngridientsViewHolder viewHolder)
            {
                var currentModel = EditIngredients[position];
                
                // 绑定初始数据
                viewHolder.IngredientName.Text = currentModel.Name;
                viewHolder.IngredientQuantity.Text = currentModel.Quantity.ToString();
                int measurementId = (int)(MeasurementEnum)Enum.Parse(typeof(MeasurementEnum), currentModel.Measurement);
                viewHolder.IngredientMeasurement.SetSelection(measurementId);

                // 名称输入监听：实时更新数据源
                viewHolder.IngredientName.TextChanged += (s, e) =>
                {
                    currentModel.Name = viewHolder.IngredientName.Text;
                };

                // 数量输入监听：实时更新数据源（做格式校验）
                viewHolder.IngredientQuantity.TextChanged += (s, e) =>
                {
                    if (double.TryParse(viewHolder.IngredientQuantity.Text, out var validQuantity))
                    {
                        currentModel.Quantity = validQuantity;
                    }
                };

                // 单位选择监听：实时更新数据源
                viewHolder.IngredientMeasurement.ItemSelected += (s, e) =>
                {
                    currentModel.Measurement = viewHolder.IngredientMeasurement.SelectedItem.ToString();
                };

                // 删除按钮逻辑：更新数据源并通知RecyclerView刷新
                viewHolder.DeleteButton.Click += (s, e) =>
                {
                    EditIngredients.RemoveAt(position);
                    NotifyItemRemoved(position);
                    NotifyItemRangeChanged(position, EditIngredients.Count);
                };
            }
        }

        public override RecyclerView.ViewHolder OnCreateViewHolder(ViewGroup parent, int viewType)
        {
            View itemView = LayoutInflater.From(parent.Context).Inflate(Resource.Layout.recipieEditIngredients_viewholder, parent, false);
            return new RecipieEditIngridientsViewHolder(itemView);
        }
    }
}

步骤3：完善ViewHolder控件绑定 #

确保ViewHolder正确获取布局中的所有可交互控件：

using Android.Views;
using AndroidX.RecyclerView.Widget;
using Google.Android.Material.TextField;

namespace Recipy.ViewHolders
{
    public class RecipieEditIngridientsViewHolder : RecyclerView.ViewHolder
    {
        public TextInputEditText IngredientName { get; }
        public TextInputEditText IngredientQuantity { get; }
        public Spinner IngredientMeasurement { get; }
        public Button DeleteButton { get; }

        public RecipieEditIngridientsViewHolder(View itemView) : base(itemView)
        {
            IngredientName = itemView.FindViewById<TextInputEditText>(Resource.Id.editRecipieNameTextField);
            IngredientQuantity = itemView.FindViewById<TextInputEditText>(Resource.Id.editRecipieQuantityTextField);
            IngredientMeasurement = itemView.FindViewById<Spinner>(Resource.Id.editRecipieMeasurementDropDown);
            DeleteButton = itemView.FindViewById<Button>(Resource.Id.deleteRowButton);
        }
    }
}

步骤4：在页面中实现保存逻辑 #

在保存按钮的点击事件中，直接从Adapter获取修改后的数据源，执行数据库更新：

// 初始化Adapter和RecyclerView（假设recipieId是当前食谱ID）
var editAdapter = new RecipieEditAdapter(recipieId);
_recipieEditIngredients.SetAdapter(editAdapter);

// 绑定保存按钮点击事件
recipieConfirmChangesButton.Click += (s, e) =>
{
    // 获取所有修改后的食材数据
    var updatedIngredients = editAdapter.EditIngredients;
    
    // 遍历数据，更新到数据库
    foreach (var ingredient in updatedIngredients)
    {
        // 调用你的数据库更新方法，示例：
        editAdapter._database.UpdateRecipieIngredient(recipieId, ingredient.IngredientId, ingredient.Name, ingredient.Quantity, ingredient.Measurement);
    }
    
    // 保存完成后返回上一页或提示用户
    Finish();
};

为什么之前的方法无效？ #

RecyclerView的核心机制是视图回收复用，屏幕外的Item View会被销毁或重新绑定到其他位置的数据，此时通过FindViewHolderForAdapterPosition获取的要么是null，要么是已复用的错误数据，无法可靠获取原始位置的输入内容。只有维护与UI同步的数据源，才能确保保存时拿到所有修改后的内容。

内容的提问来源于stack exchange，提问作者Kiril