blocks|key|169552|text|dt是nullable，您需要访问其Value|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|169553|if+(datetime.HasValue)
++++dt+=+datetime.Value;|code-block|syntax|javascript|169554|重要的是要记住，它可以是NULL。这就是为什么nullable结构具有HasValue属性来告诉您它是否是NULL。|169555|您还可以使用null-coalescing+operator+??指定缺省值|169556|dt+=+datetime+??+DateTime.Now;|169557|如果左边的值为NULL，这将赋值给右边的值|169558|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/vstudio/ms173224.aspx^0|0|2|3|8|I|5|0|0|C|4|N|8|Z|8|1H|4|0|6|O|V|2|6|O|0|0|0|7|4|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|17|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|18|8|@$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]|$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|1H|8|@$9|1I|A|1J|B|C]|$9|1K|A|1L|B|C]]|D|@$9|1M|A|1N|1|1O]]|E|$]]|$1|O|3|P|5|H|7|1P|8|@]|D|@]|E|$I|J]]|$1|Q|3|R|5|6|7|1Q|8|@$9|1R|A|1S|B|C]]|D|@]|E|$]]|$1|S|3|-4|5|6|7|1T|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]]]

<code>dt</code> is <code>nullable</code> you need to access its <code>Value</code>

<pre><code>if (datetime.HasValue)
 dt = datetime.Value;
</code></pre>

It is important to remember that it can be <code>NULL</code>. That is why the <code>nullable</code>struct has the <code>HasValue</code> property that tells you if it is <code>NULL</code> or not.

You can also use the <a href="http://msdn.microsoft.com/en-us/library/vstudio/ms173224.aspx" rel="noreferrer"><code>null-coalescing operator</code></a> <code>??</code> to assign a default value

<pre><code>dt = datetime ?? DateTime.Now;
</code></pre>

This will assign the value on the right if the value on the left is <code>NULL</code>

blocks|key|2770210|text|您应该使用datetime参数的.Value。所有可空结构都有一个value属性，该属性返回对象的具体类型。但是你必须事先检查它是否为null，否则你会得到一个运行时错误。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2770211|即：|2770212|datetime.Value|code-block|syntax|javascript|2770213|但是先检查一下它是否有值！|2770214|if+(datetime.HasValue)
{
+++//+work+with+datetime.Value
}|2770215|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

you should be using the .Value of the datetime parameter.
All Nullable structs have a value property which returns the concrete type of the object. but you must check to see if it is null beforehand otherwise you will get a runtime error.

i.e:

<pre><code>datetime.Value
</code></pre>

but check to see if it has a value first!

<pre><code>if (datetime.HasValue)
{
 // work with datetime.Value
}
</code></pre>

blocks|key|2983251|text|您有3个选项：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2983252|1)获取默认值|2983253|dt+=+datetime??DateTime.Now;|code-block|syntax|javascript|2983254|如果datetime为空，它将分配DateTime.Now+(或您想要的任何其他值|offset|length|style|CODE|2983255|2)检查datetime是否包含值，如果不包含则返回空字符串|2983256|if(!datetime.HasValue)+return+"";
dt+=+datetime.Value;|2983257|3)修改方法签名为|2983258|public+string+ConvertToPersianToShow(DateTime++datetime)|2983259|这都是因为DateTime?意味着它是可以为空的DateTime，所以在将它赋值给DateTime之前，您需要检查它是否包含值，然后再赋值。|2983260|entityMap^0|0|0|0|2|8|H|C|0|0|0|0|0|5|9|O|8|15|8|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|11|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|13|8|@$K|14|L|15|M|N]|$K|16|L|17|M|N]]|9|@]|A|$]]|$1|O|3|P|5|6|7|18|8|@]|9|@]|A|$]]|$1|Q|3|R|5|F|7|19|8|@]|9|@]|A|$G|H]]|$1|S|3|T|5|6|7|1A|8|@]|9|@]|A|$]]|$1|U|3|V|5|F|7|1B|8|@]|9|@]|A|$G|H]]|$1|W|3|X|5|6|7|1C|8|@$K|1D|L|1E|M|N]|$K|1F|L|1G|M|N]|$K|1H|L|1I|M|N]]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1J|8|@]|9|@]|A|$]]]|Z|$]]

You have 3 options:

1) Get default value

<pre><code>dt = datetime??DateTime.Now;
</code></pre>

it will assign <code>DateTime.Now</code> (or any other value which you want) if <code>datetime</code> is null

2) Check if datetime contains value and if not return empty string

<pre><code>if(!datetime.HasValue) return "";
dt = datetime.Value;
</code></pre>

3) Change signature of method to 

<pre><code>public string ConvertToPersianToShow(DateTime datetime)
</code></pre>

It's all because <code>DateTime?</code> means it's nullable <code>DateTime</code> so before assigning it to <code>DateTime</code> you need to check if it contains value and only then assign.

blocks|key|168482|text|问题在于，您正在将nullable+type传递给不可为空的类型。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|168483|您可以执行以下任一解决方案：|168484|A.将dt声明为可空|style|CODE|168485|DateTime?+dt+=+dateTime;|168486|B.使用DateTime?+datetime的Value属性|168487|DateTime+dt+=+datetime.Value;|168488|C.铸造它|168489|DateTime+dt+=+(DateTime)+datetime;|168490|entityMap|0|LINK|mutability|MUTABLE|url|https://msdn.microsoft.com/en-us/library/2cf62fcy.aspx^0|9|D|0|0|0|3|2|0|0|O|0|4|I|N|5|0|0|T|0|0|0|Y|0^^$0|@$1|2|3|4|5|6|7|11|8|@]|9|@$A|12|B|13|1|14]]|C|$]]|$1|D|3|E|5|6|7|15|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|16|8|@$A|17|B|18|H|I]]|9|@]|C|$]]|$1|J|3|K|5|6|7|19|8|@$A|1A|B|1B|H|I]]|9|@]|C|$]]|$1|L|3|M|5|6|7|1C|8|@$A|1D|B|1E|H|I]|$A|1F|B|1G|H|I]]|9|@]|C|$]]|$1|N|3|O|5|6|7|1H|8|@$A|1I|B|1J|H|I]]|9|@]|C|$]]|$1|P|3|Q|5|6|7|1K|8|@]|9|@]|C|$]]|$1|R|3|S|5|6|7|1L|8|@$A|1M|B|1N|H|I]]|9|@]|C|$]]|$1|T|3|-4|5|6|7|1O|8|@]|9|@]|C|$]]]|U|$V|$5|W|X|Y|C|$Z|10]]]]

The problem is that you are passing a <a href="https://msdn.microsoft.com/en-us/library/2cf62fcy.aspx" rel="noreferrer">nullable type</a> to a non-nullable type. 

You can do any of the following solution:

A. Declare your <code>dt</code> as nullable 

<code>DateTime? dt = dateTime;</code>

B. Use <code>Value</code> property of the the <code>DateTime? datetime</code>

<code>DateTime dt = datetime.Value;</code>

C. Cast it

<code>DateTime dt = (DateTime) datetime;</code>

I am trying to convert <code>DateTime?</code> to <code>DateTime</code> but I get this Error:
<blockquote>
Error 7 Cannot implicitly convert type 'System.DateTime?' to
'System.DateTime'. An explicit conversion exists
</blockquote>
Here is my code:
<pre><code>public string ConvertToPersianToShow(DateTime? datetime)
{
 DateTime dt;
 string date;
 dt = datetime;
 
 string year = Convert.ToString(persian_date.GetYear(dt));
 string month = Convert.ToString(persian_date.GetMonth(dt));
 string day = Convert.ToString(persian_date.GetDayOfMonth(dt));
 
 if (month.Length == 1)
 {
 month = &quot;0&quot; + Convert.ToString(persian_date.GetMonth(dt));
 }
 if (day.Length == 1)
 {
 day = &quot;0&quot; + Convert.ToString(persian_date.GetDayOfMonth(dt));
 }

 //date = Convert.ToString(persian_date.GetYear(dt)) + &quot;/&quot; + 
 Convert.ToString(persian_date.GetMonth(dt)) + &quot;/&quot; +
 //Convert.ToString(persian_date.GetDayOfMonth(dt));
 date = year + &quot;/&quot; + month + &quot;/&quot; + day+&quot;(&quot;+dt.Hour+&quot;:&quot;+dt.Minute+&quot;)&quot;;

 return date;
}
</code></pre>

Cannot implicitly convert type 'System.DateTime?' to 'System.DateTime'. An explicit conversion exists

我正在尝试将DateTime?转换为DateTime，但是我得到了这个错误：错误7不能隐式转换类型'System.DateTime?‘设置为“System.DateTime”。存在显式转换下面是我的代码：public string ConvertToPersianToShow(DateTime?  datetime){...

问无法隐式转换类型“”System.DateTime？“”设置为“System.DateTime”。存在显式转换
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问无法隐式转换类型“”System.DateTime？“”设置为“System.DateTime”。存在显式转换EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问无法隐式转换类型“”System.DateTime？“”设置为“System.DateTime”。存在显式转换
EN