datagridview-cascade-combobox ソースコード全文

<Solution>
  <Project Path="DataGridView_Cascade_Combobox/DataGridView_Cascade_Combobox.csproj" />
</Solution>

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net10.0-windows</TargetFramework>
    <Nullable>enable</Nullable>
    <UseWindowsForms>true</UseWindowsForms>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

</Project>

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="Current" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
    <ItemGroup>
        <Compile Update="Form1.cs">
            <SubType>Form</SubType>
        </Compile>
    </ItemGroup>
</Project>

using System.Data;

namespace DataGridView_Cascade_Combobox
{
    public partial class Form1 : Form
    {
        private DataTable _dataTable = new DataTable();

        public Form1()
        {
            InitializeComponent();
            InitializeDataGridView();
        }

        private void InitializeDataGridView()
        {
            // 1. グリッドにバインドするメインのデータテーブル
            _dataTable.Columns.Add("Category", typeof(string)); // 分類
            _dataTable.Columns.Add("Product", typeof(string));  // 商品名

            // テスト用の初期データ（家電と食品が混在）
            _dataTable.Rows.Add("家電", "テレビ");
            _dataTable.Rows.Add("食品", "リンゴ");

            // 2. DataGridViewの列を手動で構成
            // 【分類列の設定】
            var colCategory = new DataGridViewComboBoxColumn();
            colCategory.Name = "Category";
            colCategory.HeaderText = "分類";
            colCategory.DataSource = new string[] { "家電", "食品" };
            dataGridView1.Columns.Add(colCategory);

            // 【商品名列の設定】
            var colProduct = new DataGridViewComboBoxColumn();
            colProduct.Name = "Product";
            colProduct.HeaderText = "商品名";

            // 列全体のDataSourceには、描画エラーを防ぐために「すべての選択肢」を網羅しておきます
            colProduct.DataSource = new string[] { "テレビ", "冷蔵庫", "リンゴ", "バナナ" };
            dataGridView1.Columns.Add(colProduct);

            // データソースの適用
            dataGridView1.DataSource = _dataTable;
            dataGridView1.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.Fill;

            // 3. 必要なイベントを購読
            dataGridView1.EditingControlShowing += DataGridView1_EditingControlShowing;
            dataGridView1.DataError += DataGridView1_DataError;
        }

        /// <summary>
        /// セルが編集状態になり、内部のテキストボックスやコンボボックスが表示されたときに発生
        /// </summary>
        private void DataGridView1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
        {
            // 編集用コントロールが ComboBox（ドロップダウン）であるか確認
            if (e.Control is ComboBox comboBox)
            {
                // 現在編集しようとしているセルの列名を取得
                string columnName = dataGridView1.Columns[dataGridView1.CurrentCell.ColumnIndex].Name;

                // 商品名列のコンボボックスが開かれたタイミングで、選択肢を絞り込む
                if (columnName == "Product")
                {
                    // 現在の行の「分類（Category）」に何が入っているかを取得
                    string category = dataGridView1.CurrentRow.Cells["Category"].Value?.ToString() ?? "";

                    // 分類の値に応じて、目の前のコンボボックスコントロールのDataSourceだけを上書きする
                    if (category == "家電")
                    {
                        comboBox.DataSource = new string[] { "テレビ", "冷蔵庫" };
                    }
                    else if (category == "食品")
                    {
                        comboBox.DataSource = new string[] { "リンゴ", "バナナ" };
                    }
                    else
                    {
                        // 分類が未選択などの場合は選択肢を空にする
                        comboBox.DataSource = new string[] { };
                    }
                }
            }
        }

        /// <summary>
        /// DataGridViewの内部処理でデータ不整合などの例外が発生したときに呼び出されるイベント
        /// </summary>
        private void DataGridView1_DataError(object sender, DataGridViewDataErrorEventArgs e)
        {
            // 実務における予期せぬ「DataErrorダイアログ」の強制ポップアップを防ぐ防衛コードです。
            // 例外をシステム上方にスローしないように設定し、画面のフリーズやクラッシュを未然に防ぎます。
            e.ThrowException = false;
        }
    }
}

namespace DataGridView_Cascade_Combobox
{
    partial class Form1
    {
        /// <summary>
        ///  Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        ///  Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        ///  Required method for Designer support - do not modify
        ///  the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            dataGridView1 = new DataGridView();
            ((System.ComponentModel.ISupportInitialize)dataGridView1).BeginInit();
            SuspendLayout();
            //
            // dataGridView1
            //
            dataGridView1.ColumnHeadersHeightSizeMode = DataGridViewColumnHeadersHeightSizeMode.AutoSize;
            dataGridView1.Dock = DockStyle.Fill;
            dataGridView1.Location = new Point(0, 0);
            dataGridView1.Name = "dataGridView1";
            dataGridView1.RowHeadersWidth = 62;
            dataGridView1.Size = new Size(800, 450);
            dataGridView1.TabIndex = 0;
            //
            // Form1
            //
            AutoScaleDimensions = new SizeF(10F, 25F);
            AutoScaleMode = AutoScaleMode.Font;
            ClientSize = new Size(800, 450);
            Controls.Add(dataGridView1);
            Name = "Form1";
            Text = "Form1";
            ((System.ComponentModel.ISupportInitialize)dataGridView1).EndInit();
            ResumeLayout(false);
        }

        #endregion

        private DataGridView dataGridView1;
    }
}

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namespace DataGridView_Cascade_Combobox
{
    internal static class Program
    {
        /// <summary>
        ///  The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            // To customize application configuration such as set high DPI settings or default font,
            // see https://aka.ms/applicationconfiguration.
            ApplicationConfiguration.Initialize();
            Application.Run(new Form1());
        }
    }
}