日期時間和字串如何轉換? 如果沒有時間，DateTimePicker如何顯示空白?

日期時間和字串如何轉換? 如果沒有時間，DateTimePicker如何顯示空白?

- 將DateTimePicker的值(日期時間)轉為字串 :
  string myDate = myDateTimePicker.Value.ToString("yyyyMMdd");
  string myDateTime = myDateTimePicker.Value.ToString("yyyyMMddHHmmss");

- 將系統時間轉字串
  string myDateTime = DateTime.Now.ToString("yyyyMMddHHmmss");

- 將字串轉為DateTimePicker的值(日期時間):
  myDateTimePicker.Value = DateTime.Parse(myDateTimeString);

- DateTimePicker如何顯示特定的日期格式:
  myDateTimePicker.CustomFormat = "yyyy-MM-dd HH:mm:ss";
  myDateTimePicker.Value = DateTime.Parse(myDateTimeString);

 - 如果沒有時間，DateTimePicker如何顯示空白?
  myDateTimePicker.CustomFormat = " ";
  myDateTimePicker.Format = DateTimePickerFormat.Custom;

- 一個範例程式:

//the myDateTimeString is a string.
//the myDateTimePicker is a DateTimePicker control

if (myDateTimeString.Length == 14)
{
    //if myDateTimeString is not blank; ex, myDateTimeString = "20190125153050"
    myDateTimeString = myDateTimeString.Substring(0, 4) + "-" + myDateTimeString.Substring(4, 2) + "-" + myDateTimeString.Substring(6, 2) 
   + " " + 
   myDateTimeString.Substring(8, 2) + ":" + myDateTimeString.Substring(10, 2) + ":" + myDateTimeString.Substring(12, 2);
    myDateTimePicker.CustomFormat = "yyyy-MM-dd HH:mm:ss";
    myDateTimePicker.Value = DateTime.Parse(myDateTimeString);
}
else
{
    //if myDateTimeString is empty, make the column show blank.
    myDateTimePicker.CustomFormat = " ";
    myDateTimePicker.Format = DateTimePickerFormat.Custom;
}

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