日付型の列では、条件フィルタのフィルタエディタに、既定で "yyyy/MM/dd" 形式で日付が表示されます。

この書式を "MM/dd" 形式に変更するには、MouseClickイベントにて、内部で使用されているDateTimePickerコントロールを取得し、そのCustomFormatを "MM/dd" に設定します。

以下に、簡単な設定例を記載します。


◎サンプルコード（VB）

Imports C1.Win.C1FlexGrid

Public Class Form1
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        ' 列の設定
        C1FlexGrid1.Cols(1).DataType = GetType(DateTime)
        ' 値の設定
        For i As Integer = 0 To 4
            C1FlexGrid1(i, 1) = DateTime.Today.AddDays(i)
        Next

        ' フィルタの設定
        C1FlexGrid1.AllowFiltering = True
        C1FlexGrid1.Cols(1).AllowFiltering = AllowFiltering.ByCondition
    End Sub

    Private Sub C1FlexGrid1_MouseClick(sender As Object, e As MouseEventArgs) Handles C1FlexGrid1.MouseClick
        If (C1FlexGrid1.HitTest(e.Location).Type = HitTestTypeEnum.FilterIcon) Then
            For Each frm As Form In Application.OpenForms
                If ((frm.Name = "FilterEditorForm") _
                            AndAlso (frm.GetType.ToString = "C1.Win.C1FlexGrid.FilterEditorForm")) Then
                    ' 内部コントロールの設定変更
                    Dim panel As TableLayoutPanel = CType(frm.Controls(1).Controls(0), TableLayoutPanel)
                    If (Not (panel) Is Nothing) Then
                        panel.ColumnStyles(2).Width = 150
                        For Each c As Control In panel.Controls
                            If (TypeOf c Is DateTimePicker) Then
                                c.Width = 80
                                CType(c, DateTimePicker).Format = DateTimePickerFormat.Custom
                                CType(c, DateTimePicker).CustomFormat = "MM/dd"  '条件フィルタの書式設定
                            End If
                        Next
                    End If
                    Exit For
                End If
            Next
        End If
    End Sub
End Class

◎サンプルコード（C#）

using C1.Win.C1FlexGrid;

namespace _20220622c
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            // 列の設定
            c1FlexGrid1.Cols[1].DataType = typeof(DateTime);
            // 値の設定
            for (var i = 1; i < 5; i++)
            {
                c1FlexGrid1[i, 1] = DateTime.Today.AddDays(i);
            }

            // フィルタの設定
            c1FlexGrid1.AllowFiltering = true;
            c1FlexGrid1.Cols[1].AllowFiltering = AllowFiltering.ByCondition;
        }

        private void c1FlexGrid1_MouseClick(object sender, MouseEventArgs e)
        {
            if (c1FlexGrid1.HitTest(e.Location).Type == HitTestTypeEnum.FilterIcon)
            {
                foreach (Form frm in Application.OpenForms)
                {
                    if (frm.Name == "FilterEditorForm" && frm.GetType().ToString() == "C1.Win.C1FlexGrid.FilterEditorForm")
                    {
                        // 内部コントロールの設定変更
                        TableLayoutPanel panel = frm.Controls[1].Controls[0] as TableLayoutPanel;
                        if (panel != null)
                        {
                            panel.ColumnStyles[2].Width = 150;
                            foreach (Control c in panel.Controls)
                            {
                                if (c is DateTimePicker)
                                {
                                    c.Width = 80;
                                    (c as DateTimePicker).Format = DateTimePickerFormat.Custom;
                                    (c as DateTimePicker).CustomFormat = "MM/dd"; //条件フィルタの書式設定
                                }
                            }
                        }
                        break;
                    }
                }
            }
        }
    }
}