将datetime转换为另一种格式 [英] Convert datetime into another format

问题描述

我在VB中有以下代码。我在DateTime中有一个变量，我试图将返回值的格式从数据库转换为yyyy-MM-dd HH：mm：ss我试图将其转换为字符串，以便我可以改变其格式但似乎不是按预期工作。以下是我的代码：

Hi I have the following codes in VB. I have a variable in DateTime and I tried to convert the format of returned value from database into yyyy-MM-dd HH:mm:ss I have tried to convert it into string so that I may alter its format but seems like it does not work as expected. Below is my codes:

Dim woStartDate As DateTime
While readerSQL.Read()
      If Not IsDBNull(readerSQL.Item("WOStartDate")) Then
         woStartDate = readerSQL.Item("WOStartDate") '11/8/2016 1.52 PM
         woStartDate = woStartDate.ToString("yyyy-MM-dd HH:mm:ss") '2016-11-08 13:52:21(expected result)
      Else
         woStartDate = DateTime.Now
      End If
End While

价值留在转换后的原始格式相同。我已经多次使用过这个功能（在其他程序中）并且转换似乎没有任何问题。



我尝试了什么：



1.尝试将readerSQL.Item（WOStartDate）直接转换为字符串但返回错误。

The value stay in the same original format after conversion. I have used this function plenty of times(in other program) and it seems not have any problem converting.

What I have tried:

1. Tried to convert readerSQL.Item("WOStartDate") into string directly but returns error.

推荐答案

尝试使用它：

try to use this :

woStartDate  =  DateTime.ParseExact(woStartDate , "MM/dd/yyyy h:mm:ss tt",
           Globalization.CultureInfo.InvariantCulture)

对不起......我用错误的方式阅读了代码。

试试这段代码：

Sorry ... I read the code in the wrong way.
Try this code :

Dim woStartDate As DateTime
dim myStartDate as string
While readerSQL.Read()
      If Not IsDBNull(readerSQL.Item("WOStartDate")) Then
         woStartDate = readerSQL.Item("WOStartDate") '11/8/2016 1.52 PM
         myStartDate = woStartDate.ToString("yyyy-MM-dd HH:mm:ss") '2016-11-08 13:52:21(expected result)
      Else
         myStartDate = DateTime.Now.tostring
      End If
End While

AD ate或DateTime就是这个。

只有一个字符串可以保存不同的格式...

A Date or a DateTime is simply this.
Only a string could hold a different formatting ...

一个DateTime变量没有格式，它代表一个时间点。只有在将其转换为字符串时才会获得格式。当您只是要求DateTime变量将其自身显示为字符串时，它会选择在操作系统的系统设置中定义的格式，如果您希望以特定格式使用，则需要通过ToString提供该格式。 DateTime变量本身虽然没有格式，但是当你显示它时你真正看到的是它的默认表示。



基本上，你不能给DateTime一种格式，你不能用SQL格式给出日期，只有当你将它们转换为字符串时才给出日期格式，所以保留原样并在需要显示它们时转换它们。

A DateTime variable doesn't have a format, it represents a point in time. It only gains a format when you convert it to a string. When you simply ask a DateTime variable to show itself as a string it chooses the format defined in the system settings of the OS, if you want it in a specific format you need to supply that format via ToString. The DateTime variable itself though doesn't have a format, what you are really seeing when you show it is its default representation.

Basically, you can't give DateTime a format, you can't give dates in SQL a format, you only give dates a format when you convert them to string so leave them as they are and convert them when you need to display them.

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