datagridview-add-new-row-default-value ソースコード全文

<Solution>
  <Project Path="DataGridView_AddNewRow_Default_Value/DataGridView_AddNewRow_Default_Value.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_AddNewRow_Default_Value
{
    public partial class Form1 : Form
    {
        private DataTable _dataTable = new DataTable();

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

        private void InitializeDataGridView()
        {
            // テスト用データの準備
            _dataTable.Columns.Add("Code", typeof(string));
            _dataTable.Columns.Add("Name", typeof(string));
            _dataTable.Columns.Add("Count", typeof(int));
            _dataTable.Columns.Add("Date", typeof(string));

            _dataTable.Rows.Add("P001", "ノートパソコン", 1, "2026/06/01");

            dataGridView1.DataSource = _dataTable;
            dataGridView1.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.Fill;

            // 既定値設定用のイベントを購読
            dataGridView1.DefaultValuesNeeded += DataGridView1_DefaultValuesNeeded;
        }

        /// <summary>
        /// 新しい行の既定値を設定するイベント
        /// </summary>
        private void DataGridView1_DefaultValuesNeeded(object? sender, DataGridViewRowEventArgs e)
        {
            // 新規追加された行の「Count」列に初期値 1 を設定
            if (dataGridView1.Columns["Count"] != null)
            {
                e.Row.Cells["Count"].Value = 1;
            }

            // 新規追加された行の「Date」列に本日の日付（yyyy/MM/dd形式）を設定
            if (dataGridView1.Columns["Date"] != null)
            {
                e.Row.Cells["Date"].Value = DateTime.Today.ToString("yyyy/MM/dd");
            }
        }
    }
}

namespace DataGridView_AddNewRow_Default_Value
{
    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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    <resheader name="writer">System.Resources.ResXResourceWriter, System.Windows.Forms, ...</resheader>
    <data name="Name1"><value>this is my long string</value><comment>this is a comment</comment></data>
    <data name="Color1" type="System.Drawing.Color, System.Drawing">Blue</data>
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        <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>
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        <xsd:choice maxOccurs="unbounded">
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          </xsd:element>
          <xsd:element name="assembly">
            <xsd:complexType>
              <xsd:attribute name="alias" type="xsd:string" />
              <xsd:attribute name="name" type="xsd:string" />
            </xsd:complexType>
          </xsd:element>
          <xsd:element name="data">
            <xsd:complexType>
              <xsd:sequence>
                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
                <xsd:element name="comment" type="xsd:string" minOccurs="0" msdata:Ordinal="2" />
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    <value>2.0</value>
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    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
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namespace DataGridView_AddNewRow_Default_Value
{
    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());
        }
    }
}