blocks|key|1410961|text|8年后更新(哇！)要介绍c#+6's+null-conditional+operator|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1410962|var+value+=+maybeNull?.ToString()+??+String.Empty;|code-block|syntax|javascript|1410963|其他方法：|1410964|object+defaultValue+=+"default";
attribs.something+=+(entry.Properties["something"].Value+??+defaultValue).ToString()|1410965|我还使用了这个，虽然不是很聪明，但很方便：|1410966|public+static+string+ToSafeString(this+object+obj)
{
++++return+(obj+??+string.Empty).ToString();
}|1410967|entityMap|0|LINK|mutability|MUTABLE|url|https://msdn.microsoft.com/en-us/library/dn986595.aspx^0|C|W|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@$A|Z|B|10|1|11]]|C|$]]|$1|D|3|E|5|F|7|12|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|13|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|14|8|@]|9|@]|C|$G|H]]|$1|M|3|N|5|6|7|15|8|@]|9|@]|C|$]]|$1|O|3|P|5|F|7|16|8|@]|9|@]|C|$G|H]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]]]

Update 8 years later (wow!) to cover <a href="https://msdn.microsoft.com/en-us/library/dn986595.aspx" rel="noreferrer">c# 6's null-conditional operator</a>:

<pre><code>var value = maybeNull?.ToString() ?? String.Empty;
</code></pre>

Other approaches:

<pre><code>object defaultValue = "default";
attribs.something = (entry.Properties["something"].Value ?? defaultValue).ToString()
</code></pre>

I've also used this, which isn't terribly clever but convenient:

<pre><code>public static string ToSafeString(this object obj)
{
 return (obj ?? string.Empty).ToString();
}
</code></pre>

blocks|key|1411282|text|如果您的目标是.NET+Framework3.5，在我看来，最优雅的解决方案是扩展方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1411283|public+static+class+ObjectExtensions
{
++++public+static+string+NullSafeToString(this+object+obj)
++++{
++++++++return+obj+!=+null+?+obj.ToString()+:+String.Empty;
++++}
}|code-block|syntax|javascript|1411284|然后使用：|1411285|attribs.something+=+entry.Properties["something"].Value.NullSafeToString();|1411286|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|$]]

If you are targeting the .NET Framework 3.5, the most elegant solution would be an extension method in my opinion.

<pre><code>public static class ObjectExtensions
{
 public static string NullSafeToString(this object obj)
 {
 return obj != null ? obj.ToString() : String.Empty;
 }
}
</code></pre>

Then to use:

<pre><code>attribs.something = entry.Properties["something"].Value.NullSafeToString();
</code></pre>

blocks|key|1411372|text|Convert.ToString(entry.Properties["something"].Value);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1411373|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>Convert.ToString(entry.Properties["something"].Value);
</code></pre>

blocks|key|1626091|text|你能不能不这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1626092|attribs.something+=+entry.Properties["something"].Value+as+string;|code-block|syntax|javascript|1626093|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|$]]

Can you not do:

<pre><code>attribs.something = entry.Properties["something"].Value as string;
</code></pre>

blocks|key|1626258|text|attribs.something+=+String.Format("{0}",+entry.Properties["something"].Value);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1626259|虽然不确定性能...|unstyled|1626260|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>attribs.something = String.Format("{0}", entry.Properties["something"].Value);
</code></pre>

Not sure about performance though...

blocks|key|1626289|text|在C#+6.0中，你可以用一种非常优雅的方式做到这一点：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1626290|attribs.something+=+entry.Properties["something"].Value?.ToString();|offset|length|style|CODE|1626291|这里有一篇关于新null-conditional+operator的文章。|1626292|entityMap|0|LINK|mutability|MUTABLE|url|https://msdn.microsoft.com/en-us/library/dn986595.aspx^0|0|0|1W|0|8|P|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@$D|T|E|U|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|V|8|@]|9|@$D|W|E|X|1|Y]]|A|$]]|$1|J|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|K|$L|$5|M|N|O|A|$P|Q]]]]

In C# 6.0 you can do it in a very elegant way:

<code>attribs.something = entry.Properties["something"].Value?.ToString();</code>

And here is an article about new <a href="https://msdn.microsoft.com/en-us/library/dn986595.aspx" rel="nofollow">null-conditional operator</a>.

blocks|key|1625813|text|作为RexM答案的变体：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1625814|attribs.something+=+(entry.Properties["something"].Value+??+attribs.something).ToString()|code-block|syntax|javascript|1625815|唯一的缺点是，即使entry.Properties"something".Value为null，也会为attribs.something赋值(在本例中为其本身)-如果.something属性执行一些其他处理和/或此行执行很多(就像在循环中一样)，这可能是很昂贵的。|1625816|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

As a variation to RexM's answer:

<pre><code>attribs.something = (entry.Properties["something"].Value ?? attribs.something).ToString()
</code></pre>

The only downside would be that the attribs.something would be assigned a value (itself, in this example) even if entry.Properties["something"].Value was null - which could be expensive if the .something property did some other processing and/or this line executes a lot (like in a loop).

blocks|key|1625957|text|为了准确地完成你想要做的事情，总是可以使用helper方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1625958|CopyIfNotNull(entry.Properties["something"].Value,+out+attribs.something);

void+CopyIfNotNull(string+src,+out+string+dest)
{
++if(src+!=+null)
++++dest+=+src;
}|code-block|syntax|javascript|1625959|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|$]]

To do precisely what you're trying to do a helper method can always be used:

<pre><code>CopyIfNotNull(entry.Properties["something"].Value, out attribs.something);

void CopyIfNotNull(string src, out string dest)
{
 if(src != null)
 dest = src;
}
</code></pre>

blocks|key|1411352|text|attribs.something++=+string.Format("{0}",entry.Properties["something"].Value)|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1411353|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>attribs.something = string.Format("{0}",entry.Properties["something"].Value)
</code></pre>

blocks|key|1411457|text|有没有可能做一些像Dale+Ragan's+answer+above这样的事情，但是覆盖ToString()而不是创建一个新的NullSafeToString()方法？我希望这(或返回"null")成为默认行为。当我将以下方法添加到公共静态类ObjectExtensions中时，编译器(Visual+C#+2010Express)不会报错，但该方法没有被调用...|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1411458|public+static+String+ToString(this+Object+obj)
{
++++if+(obj+==+null)
++++{
++++++++return+"null";
++++}
++++else
++++{
++++++++return+obj.GetType().Name;
++++}
}|code-block|syntax|javascript|1411459|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/550374/checking-for-null-before-tostring/550399#550399^0|9|P|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Is it somehow possible to do something like 
<a href="https://stackoverflow.com/questions/550374/checking-for-null-before-tostring/550399#550399">Dale Ragan's answer above</a>, but overriding ToString() instead of creating a new NullSafeToString() method? I'd like this (or returning "null") to be the default behaviour. The compiler (Visual C# 2010 Express) doesn't complain when I add the following method to public static class ObjectExtensions, but the method doesn't get called...

<pre><code>public static String ToString(this Object obj)
{
 if (obj == null)
 {
 return "null";
 }
 else
 {
 return obj.GetType().Name;
 }
}
</code></pre>

blocks|key|1411129|text|使用像这样的辅助方法如何：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1411130|attribs.something+=+getString(
++++entry.Properties["something"].Value,+
++++attribs.something);

static+String+getString(
++++Object+obj,
++++String+defaultString)
{
++++if+(obj+==+null)+return+defaultString;
++++return+obj.ToString();
}|code-block|syntax|javascript|1411131|或者，您可以使用??运算符：|offset|length|style|CODE|1411132|attribs.something+=+
++++(entry.Properties["something"].Value+??+attribs.something).ToString();|1411133|(注意当值为null时的冗余ToString()调用)|1411134|entityMap^0|0|0|8|2|0|0|6|4|E|A|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@$I|V|J|W|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|Y|8|@$I|Z|J|10|K|L]|$I|11|J|12|K|L]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|R|$]]

How about using an auxiliary method like this:

<pre><code>attribs.something = getString(
 entry.Properties["something"].Value, 
 attribs.something);

static String getString(
 Object obj,
 String defaultString)
{
 if (obj == null) return defaultString;
 return obj.ToString();
}
</code></pre>

Alternatively, you could use the <code>??</code> operator:

<pre><code>attribs.something = 
 (entry.Properties["something"].Value ?? attribs.something).ToString();
</code></pre>

(note the redundant <code>ToString()</code> call when the value is <code>null</code>)

Here's the scenario... 

<pre><code>if (entry.Properties["something"].Value != null)
 attribs.something = entry.Properties["something"].Value.ToString();
</code></pre>

While effective and working correctly, this looks ugly to me. If I don't check for a null before performing the ToString() then it throws an exception if the property was null. Is there a better way to handle this scenario?

Much appreciated!

Checking for null before ToString()

这是一个场景..。if (entry.Properties["something"].Value != null)  attribs.something = entry.Properties["something"].Value.ToString();虽然有效且工作正常，但在我看来这看起来很丑陋。如果我在执行ToString()之前没有检查null，那么如果属性为null，它就会抛出一个异常。有没

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