C# 如何转换日期时间？到日期时间
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how to convert datetime? to datetime
提问by
I have filed txtb_dateOfServiceis required to complete the form but if txtb_dateOfServiceis emapty return null if not TryParse the date >I had this error I don't know how to fix it
我已经提交txtb_dateOfService了完成表格但如果txtb_dateOfService是 emapty 返回 null 如果不是 TryParse>我遇到这个错误的日期我不知道如何解决它
The best overloaded method match for 'System.DateTime.TryParse(string, out System.DateTime)' has some invalid arguments
'System.DateTime.TryParse(string, out System.DateTime)' 的最佳重载方法匹配有一些无效参数
DateTime? dateOfService= null;
if (string.IsNullOrEmpty(txtb_dateOfService.Text))
{
dateOfService = null;
}
else
if (DateTime.TryParse(txtb_dateOfService.Text, out dateOfService))
{
}
采纳答案by dasblinkenlight
You cannot pass a reference to DateTime?into a method expecting DateTime. You can solve this by introducing a temporary variable, like this:
您不能将引用传递DateTime?到期望 的方法中DateTime。您可以通过引入一个临时变量来解决这个问题，如下所示：
else { // <<=== This is the final "else" from your code
DateTime tmp;
if (DateTime.TryParse(txtb_dateOfService.Text, out tmp))
{
dateOfService = tmp;
} else {
dateOfService = null;
}
}
回答by Preston Guillot
Your problem is converting DateTime?to DateTime, not vice versa. The DateTime.TryParsemethod's outparameter is not nullable; in the event TryParsefails the out parameter will be assigned DateTime.MinValueas its value. There is no reason to declare your dateOfServicevariable as a nullable type from this snippet.
您的问题正在转换DateTime?为DateTime，而不是相反。该DateTime.TryParse方法的out参数不可为空；如果TryParse失败，out 参数将被分配DateTime.MinValue为其值。没有理由在dateOfService此代码段中将您的变量声明为可空类型。
回答by D Stanley
You can either throw an exception if the parse fails:
如果解析失败，您可以抛出异常：
DateTime? dateOfService= null;
if (string.IsNullOrEmpty(txtb_dateOfService.Text))
{
dateOfService = null;
}
else
{
// will throw an exception if the text is not parseable
dateOfService = DateTime.Parse(txtb_dateOfService.Text);
}
or use an intermediate DateTime to store the parsed result:
或使用中间 DateTime 来存储解析结果：
DateTime? dateOfService= null;
if (string.IsNullOrEmpty(txtb_dateOfService.Text))
{
dateOfService = null;
}
else
{
DateTime temp;
if (DateTime.TryParse(txtb_dateOfService.Text, out temp))
{
dateOfService = temp;
}
else
{
dateOfService = null;
}
}
Either of these can be logically simplified; I'm showing the full breakout to convey the logic.
其中任何一个都可以在逻辑上简化；我正在展示完整的突破来传达逻辑。
回答by Felipe Oriani
You can try to convert your stringin a DateTime
您可以尝试将您string的DateTime
DateTime? dataOfService = null;
DateTime output;
if (DateTime.TryParse(txtb_dateOfService.Text, out output))
dataOfService = output;
now you can use dataOfServiceas a Nullable<DateTime>and check if it has a valid data converted using HasValueand Valueproperties.
现在您可以dataOfService用作 aNullable<DateTime>并检查它是否具有使用HasValue和Value属性转换的有效数据。
回答by Charles Lambert
you need to create a temp value to hold the out parameter of TryParse:
您需要创建一个临时值来保存以下参数TryParse：
DateTime tmp;
if (DateTime.TryParse(txtb_dateOfService.Text, out tmp)) {
dateOfService = tmp;
} else{
dateOfService = null;
}
A more terse example
一个更简洁的例子
DateTime tmp;
DateTime? dateOfService = DateTime.TryParse(txtb_dateOfService.Text, out tmp)
? tmp
: (DateTime?)null;
回答by It'sNotALie.
try out dateOfService.Value, this should work (I think)
尝试 dateOfService.Value，这应该可行（我认为）
