問題描述

更改 .NET DateTimePicker 控件以允許用戶輸入 null 值的最簡單、最可靠的方法是什么?

What's the easiest and most robust way of altering the .NET DateTimePicker control, to allow users to enter null values?

推薦答案

這是 CodeProject 文章中關于創建 可以為空的 DateTimePicker.

Here's an approach from this CodeProject article on creating a Nullable DateTimePicker.

我已覆蓋 Value 屬性以接受 Null 值作為 DateTime.MinValue，同時保持 MinValue 的驗證標準控件的code>和MaxValue.

I have overridden the Value property to accept Null value as DateTime.MinValue, while maintaining the validation of MinValue and MaxValue of the standard control.

這是文章中自定義類組件的一個版本

Here's a version of the custom class component from the article

public class NullableDateTimePicker : System.Windows.Forms.DateTimePicker
{
    private DateTimePickerFormat originalFormat = DateTimePickerFormat.Short;
    private string originalCustomFormat;
    private bool isNull;

    public new DateTime Value
    {
        get => isNull ? DateTime.MinValue : base.Value;
        set
        {
            // incoming value is set to min date
            if (value == DateTime.MinValue)
            {
                // if set to min and not previously null, preserve original formatting
                if (!isNull)
                {
                    originalFormat = this.Format;
                    originalCustomFormat = this.CustomFormat;
                    isNull = true;
                }

                this.Format = DateTimePickerFormat.Custom;
                this.CustomFormat = " ";
            }
            else // incoming value is real date
            {
                // if set to real date and previously null, restore original formatting
                if (isNull)
                {
                    this.Format = originalFormat;
                    this.CustomFormat = originalCustomFormat;
                    isNull = false;
                }

                base.Value = value;
            }
        }
    }

    protected override void OnCloseUp(EventArgs eventargs)
    {
        // on keyboard close, restore format
        if (Control.MouseButtons == MouseButtons.None)
        {
            if (isNull)
            {
                this.Format = originalFormat;
                this.CustomFormat = originalCustomFormat;
                isNull = false;
            }
        }
        base.OnCloseUp(eventargs);
    }

    protected override void OnKeyDown(KeyEventArgs e)
    {
        base.OnKeyDown(e);

        // on delete key press, set to min value (null)
        if (e.KeyCode == Keys.Delete)
        {
            this.Value = DateTime.MinValue;
        }
    }
}

這篇關于如何更改 .NET DateTimePicker 控件以允許輸入空值?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！