SharePoint查询日期格式转换问题：转MM/dd/yyyy 12小时制

Hey there! The issue here is that you’re trying to apply date formatting directly to a string value (dateInfo), but String.Format can only use those date-specific format specifiers on actual DateTime objects—not plain strings. Here’s how to fix this:

Step 1: Convert the SharePoint date string to a DateTime object #

First, you need to parse the raw date string from SharePoint into a DateTime instance. You can use DateTime.Parse for straightforward cases, or DateTime.TryParse if you want to handle invalid date strings gracefully (to avoid exceptions):

// Option 1: Direct parse (throws exception if the string is invalid)
DateTime alteredDate = DateTime.Parse(xNode.Attributes["Altered"].Value);

// Option 2: Safer TryParse (no exception, validates the date first)
if (DateTime.TryParse(xNode.Attributes["Altered"].Value, out DateTime alteredDate))
{
    // Proceed with formatting
}
else
{
    // Handle invalid date case (e.g., append an error message)
    sb.Append("Invalid date");
}

Step 2: Format the DateTime to your desired 12-hour format #

Now that you have a DateTime object, you can format it using the correct specifiers. Based on your request (month/day/year with 12-hour time), use the format string "MM/dd/yyyy h:mm:ss tt"—this will produce something like 04/27/2023 4:27:12 PM.

A quick critical note: MM stands for two-digit months, while mm stands for minutes. Make sure you use MM for the month part (matching your original code’s intent). If you don’t want the AM/PM indicator, omit the tt segment to get 04/27/2023 4:27:12.

Putting it all together, here’s the full working code:

string rawDate = xNode.Attributes["Altered"].Value;
if (DateTime.TryParse(rawDate, out DateTime alteredDate))
{
    // Format with AM/PM (matches your 12-hour requirement)
    sb.Append(string.Format("{0:MM/dd/yyyy h:mm:ss tt}", alteredDate));
    
    // Or without AM/PM:
    // sb.Append(string.Format("{0:MM/dd/yyyy h:mm:ss}", alteredDate));
}
else
{
    sb.Append("Invalid date value");
}

Why your original code failed #

When you pass a string to String.Format with a date specifier like {0:MM/dd/yyyy}, .NET doesn’t recognize it as a date—it treats it as plain text, so the format specifier does nothing. Converting to a DateTime first tells .NET to apply date-specific formatting rules.

That should give you exactly the format you need!

内容的提问来源于stack exchange，提问作者HotTomales