datagridview-header-checkbox-select-all-rows ソースコード全文

<Solution>
  <Project Path="DataGridView_HeaderCheckBox/DataGridView_HeaderCheckBox.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;
using System.Windows.Forms.VisualStyles; // CheckBoxRenderer を使うために必要

namespace DataGridView_HeaderCheckBox;

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

    // ヘッダーの状態を管理する変数（初期値は未チェック）
    private CheckBoxState _headerState = CheckBoxState.UncheckedNormal;

    // 一括更新中の「イベント連打」を防ぐための制御フラグ
    private bool _isUpdatingAllRows = false;

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

    private void InitializeData()
    {
        // 表示用デモデータの準備
        _dataTable.Columns.Add("ID", typeof(string));
        _dataTable.Columns.Add("Country", typeof(string));
        _dataTable.Columns.Add("City", typeof(string));

        _dataTable.Rows.Add("B-6000", "Belgium", "Charleroi");
        _dataTable.Rows.Add("04876", "Brazil", "Campinas");
        _dataTable.Rows.Add("08737", "Brazil", "Resende");
        _dataTable.Rows.Add("T2F 8M4", "Canada", "Tsawwassen");
    }

    private void InitializeDataGridView()
    {
        // 1. データソースをバインドする前に、チェックボックス列を手動で先頭に追加
        var chkColumn = new DataGridViewCheckBoxColumn();
        chkColumn.Name = "SelectChk";
        chkColumn.HeaderText = ""; // ヘッダーテキストは空にして、後から画像を描画します
        chkColumn.Width = 45;
        chkColumn.Resizable = DataGridViewTriState.False;
        dataGridView1.Columns.Add(chkColumn);

        // データのバインド
        dataGridView1.DataSource = _dataTable;

        dataGridView1.AllowUserToAddRows = false;

        // 2. 必要なイベントを購読
        dataGridView1.CellPainting += DataGridView1_CellPainting;
        dataGridView1.CellClick += DataGridView1_CellClick;
        dataGridView1.CurrentCellDirtyStateChanged += DataGridView1_CurrentCellDirtyStateChanged;
        dataGridView1.CellValueChanged += DataGridView1_CellValueChanged;
    }

    /// <summary>
    /// セルの描画イベント（ヘッダーにチェックボックスを描画する）
    /// </summary>
    private void DataGridView1_CellPainting(object? sender, DataGridViewCellPaintingEventArgs e)
    {
        // 先頭列（ColumnIndex == 0）かつ ヘッダー行（RowIndex == -1）のときのみカスタム描画
        if (e.RowIndex == -1 && e.ColumnIndex == 0)
        {
            e.PaintBackground(e.CellBounds, true);

            Size checkBoxSize = CheckBoxRenderer.GetGlyphSize(e.Graphics, CheckBoxState.UncheckedNormal);
            int x = e.CellBounds.X + (e.CellBounds.Width - checkBoxSize.Width) / 2;
            int y = e.CellBounds.Y + (e.CellBounds.Height - checkBoxSize.Height) / 2;
            Point drawPoint = new Point(x, y);

            // 現在の _headerState（Checked/Unchecked/Mixed）に基づいて描画
            CheckBoxRenderer.DrawCheckBox(e.Graphics, drawPoint, _headerState);

            e.Handled = true;
        }
    }

    /// <summary>
    /// セルまたはヘッダーがクリックされたときのイベント
    /// </summary>
    private void DataGridView1_CellClick(object? sender, DataGridViewCellEventArgs e)
    {
        // 先頭列のヘッダーがクリックされたかチェック
        if (e.RowIndex == -1 && e.ColumnIndex == 0)
        {
            // 現在編集中のデータ行があれば、その編集状態を強制終了させて確定する
            dataGridView1.EndEdit();

            // 現在「全選択」状態であれば次は「全解除」、それ以外（未選択・部分選択）なら次は「全選択」にする
            bool nextCheckValue = (_headerState != CheckBoxState.CheckedNormal);

            // イベント連打防止フラグを立てる
            _isUpdatingAllRows = true;

            // 3. 全行をループして、チェックボックスの値を一括で書き換える
            foreach (DataGridViewRow row in dataGridView1.Rows)
            {
                if (!row.IsNewRow)
                {
                    row.Cells["SelectChk"].Value = nextCheckValue;
                }
            }

            _isUpdatingAllRows = false;

            // ヘッダーの状態を更新
            _headerState = nextCheckValue ? CheckBoxState.CheckedNormal : CheckBoxState.UncheckedNormal;

            // ヘッダーだけでなく、データ行全体の見た目を確実に同期させるためグリッド全体を再描画
            dataGridView1.Invalidate();
        }
    }

    /// <summary>
    /// チェックボックスの値が確定したときに呼び出されるイベント
    /// </summary>
    private void DataGridView1_CellValueChanged(object? sender, DataGridViewCellEventArgs e)
    {
        if (e.RowIndex >= 0 && e.ColumnIndex == 0 && !_isUpdatingAllRows)
        {
            UpdateHeaderCheckBoxState();
        }
    }

    /// <summary>
    /// データ行のチェック状態をスキャンし、ヘッダーの状態を決定するメソッド
    /// </summary>
    private void UpdateHeaderCheckBoxState()
    {
        int checkedCount = 0;
        int dataRowCount = 0;

        foreach (DataGridViewRow row in dataGridView1.Rows)
        {
            if (!row.IsNewRow)
            {
                dataRowCount++;
                if (row.Cells["SelectChk"].Value is bool b && b)
                {
                    checkedCount++;
                }
            }
        }

        // チェック数に応じて、ヘッダーの状態（3つのステータス）を割り出す
        if (checkedCount == 0)
        {
            _headerState = CheckBoxState.UncheckedNormal; // 全て未選択
        }
        else if (checkedCount == dataRowCount)
        {
            _headerState = CheckBoxState.CheckedNormal;   // 全て選択
        }
        else
        {
            _headerState = CheckBoxState.MixedNormal;     // 一部のみ選択（部分選択状態）
        }

        dataGridView1.InvalidateCell(0, -1);
    }

    private void DataGridView1_CurrentCellDirtyStateChanged(object? sender, EventArgs e)
    {
        if (dataGridView1.CurrentCell is DataGridViewCheckBoxCell)
        {
            dataGridView1.CommitEdit(DataGridViewDataErrorContexts.Commit);
        }
    }
}

namespace DataGridView_HeaderCheckBox
{
    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_HeaderCheckBox
{
    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());
        }
    }
}