blocks|key|212058|text|一个简单的显式类型转换使其可编译：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|212059|decimal+temp;
//+typecast+either+'temp'+or+'null'
decimal?+numericValue+=
++decimal.TryParse(numericString,+out+temp)+?+temp+:+(decimal?)null;|code-block|syntax|javascript|212060|另一种选择是对所需的可空类型使用default运算符：|offset|length|style|CODE|212061|decimal+temp;
//+replace+null+with+default
decimal?+numericValue+=
++decimal.TryParse(numericString,+out+temp)+?+temp+:+default(decimal?);|212062|entityMap^0|0|0|G|7|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

One simple explicit typecast makes it compilable:

<pre><code>decimal temp;
// typecast either 'temp' or 'null'
decimal? numericValue =
 decimal.TryParse(numericString, out temp) ? temp : (decimal?)null;
</code></pre>

Another option is to use the <code>default</code> operator on the desired nullable type:

<pre><code>decimal temp;
// replace null with default
decimal? numericValue =
 decimal.TryParse(numericString, out temp) ? temp : default(decimal?);
</code></pre>

blocks|key|3067308|text|我会这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3067309|public+delegate+bool+TryParseDelegate<T>(string+str,+out+T+value);

public+static+T?+TryParseOrNull<T>(TryParseDelegate<T>+parse,+string+str)+where+T+:+struct
{
++++T+value;
++++return+parse(str,+out+value)+?+value+:+(T?)null;
}

decimal?+numericValue+=+TryParseOrNull<decimal>(decimal.TryParse,+numericString);|code-block|syntax|javascript|3067310|或者，您可以将其作为扩展方法：|3067311|public+static+T?+TryParseAs<T>(this+string+str,+TryParseDelegate<T>+parse)+where+T+:+struct
{
++++T+value;
++++return+parse(str,+out+value)+?+value+:+(T?)null;
}

decimal?+numericValue+=+numericString.TryParseAs<decimal>(decimal.TryParse);|3067312|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I'd do something like this:

<pre><code>public delegate bool TryParseDelegate&lt;T&gt;(string str, out T value);

public static T? TryParseOrNull&lt;T&gt;(TryParseDelegate&lt;T&gt; parse, string str) where T : struct
{
 T value;
 return parse(str, out value) ? value : (T?)null;
}

decimal? numericValue = TryParseOrNull&lt;decimal&gt;(decimal.TryParse, numericString);
</code></pre>

Or you could make it an extension method:

<pre><code>public static T? TryParseAs&lt;T&gt;(this string str, TryParseDelegate&lt;T&gt; parse) where T : struct
{
 T value;
 return parse(str, out value) ? value : (T?)null;
}

decimal? numericValue = numericString.TryParseAs&lt;decimal&gt;(decimal.TryParse);
</code></pre>

blocks|key|212641|text|只需将其分解为一个扩展方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|212642|public+static+decimal?+ParseDecimal(this+string+s)
{
++++decimal+d;
++++if+(decimal.TryParse(s,+out+d))
++++++++return+d;
++++return+null;
}|code-block|syntax|javascript|212643|然后您可以像这样使用它：|212644|numericValue+=+numericString.TryParseDecimal();|212645|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Just factorize it to an extension method:

<pre><code>public static decimal? ParseDecimal(this string s)
{
 decimal d;
 if (decimal.TryParse(s, out d))
 return d;
 return null;
}
</code></pre>

You can then use it like this:

<pre><code>numericValue = numericString.TryParseDecimal();
</code></pre>

blocks|key|212097|text|这样如何：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|212098|decimal?+numericValue+=+
++++decimal.TryParse(numericString,+out+temp)+?+temp+:+null+as+decimal?;|code-block|syntax|javascript|212099|如果类型转换失败，这将使numericValue成为null，并且很好和干净。|offset|length|style|CODE|212100|entityMap^0|0|0|Q|4|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

How about:

<pre><code>decimal? numericValue = 
 decimal.TryParse(numericString, out temp) ? temp : null as decimal?;
</code></pre>

This makes numericValue <code>null</code> if the cast fails, and is nice and clean.

blocks|key|209615|text|问题是temp是一个十进制且null...is为null。因为它们不是同一类型的，所以两者之间的比较失败，您会得到一个错误。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|209616|尝试以下任一操作：|209617|decimal?+numericValue+=+decimal.TryParse(numericString,+out+temp)+?+(decimal?)temp+:+null;|code-block|syntax|javascript|209618|或|209619|decimal?+numericValue+=+decimal.TryParse(numericString,+out+temp)+?+(decimal?)temp+:+(decimal?)null;|209620|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|$]]

The problem is that temp is a decimal and null...is null. Because they are not of the same type, the comparison between the two fails and you get an error. 

Try either:

<pre><code>decimal? numericValue = decimal.TryParse(numericString, out temp) ? (decimal?)temp : null;
</code></pre>

or

<pre><code>decimal? numericValue = decimal.TryParse(numericString, out temp) ? (decimal?)temp : (decimal?)null;
</code></pre>

blocks|key|214037|text|我认为您应该将其封装在一个方法中，以获得更好的可读性：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|214038|private+decimal?+ParseOrDefault(string+decimalAsString,+decimal?+defaultIfInvalidString=null)
{
++++decimal+result;
++++if+(decimal.TryParse(decimalAsString,+out+result))
++++++++return+result;
++++return+defaultIfInvalidString;
}

[Test]
public+void+ParseOrDefaultTest()
{
++++decimal?+actual+=+ParseOrDefault("12",+null);
++++Assert.AreEqual(12m,actual);

++++actual+=+ParseOrDefault("Invalid+string",+null);
++++Assert.AreEqual(null,+actual);
}|code-block|syntax|javascript|214039|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I think you should wrap it in a method for better readability:

<pre><code>private decimal? ParseOrDefault(string decimalAsString, decimal? defaultIfInvalidString=null)
{
 decimal result;
 if (decimal.TryParse(decimalAsString, out result))
 return result;
 return defaultIfInvalidString;
}

[Test]
public void ParseOrDefaultTest()
{
 decimal? actual = ParseOrDefault("12", null);
 Assert.AreEqual(12m,actual);

 actual = ParseOrDefault("Invalid string", null);
 Assert.AreEqual(null, actual);
}
</code></pre>

blocks|key|2853907|text|小数？权重=+decimal.TryParse(weightEditText.Text，out+var+tempWeight)？tempWeight+:默认(十进制？)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2853908|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

decimal? weight = decimal.TryParse(weightEditText.Text, out var tempWeight) ? tempWeight : default(decimal?)

Scenario

Parse a string into a nullable numeric type. If the parse is unsuccessful, the result should be null; otherwise the result should be the parsed value.

Question

To accomplish this, I have always used the following simple but lengthily annoying method:

<pre><code>string numericString = "...";

decimal? numericValue;
decimal temp;
if (decimal.TryParse(numericString, out temp))
{
 numericValue = temp;
}
else
{
 numericValue = null;
}
</code></pre>

I use the above method because the following doesn't compile:

<pre><code>decimal temp;
decimal? numericValue = decimal.TryParse(numericString, out temp) ? temp : null;
</code></pre>

Does anybody know of a version of the first bit of code that is as short, tidy, and readable as the second bit? I know I could always write an extension method that encapsulates the first bit of code, but I'm wondering if there is any way to do what I want without an extension method.

Parse string into nullable numeric type (1 or 2 liner)

方案将字符串分析为可以为空的数值类型。如果解析不成功，则结果应为空；否则，结果应为已解析的值。问题为了做到这一点，我总是使用下面这个简单但冗长的方法：string numericString = "...";decimal? numericValue;decimal temp;if (decimal.TryParse(...

问将字符串解析为可空的数字类型(1或2线性)
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