blocks|key|3281524|text|正如Mehrdad已经指出的那样，除了违反德米特定律之外，在我看来，您还需要对决策逻辑进行“深度零检查”。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3281525|当您希望用默认值替换空对象时，通常会出现这种情况。在这种情况下，您应该考虑实现Null+Object+Pattern。它充当真实对象的替身，提供默认值和“非操作”方法。|offset|length|3281526|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Null_Object_pattern^0|0|13|J|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

Besides violating the Law of Demeter, as Mehrdad Afshari has already pointed out, it seems to me you need "deep null checking" for decision logic. 

This is most often the case when you want to replace empty objects with default values. In this case you should consider implementing the <a href="http://en.wikipedia.org/wiki/Null_Object_pattern" rel="noreferrer">Null Object Pattern</a>. It acts as a stand-in for a real object, providing default values and "non-action" methods.

blocks|key|322667|text|更新：从Visual+Studio2015开始，C#编译器(语言版本6)现在可以识别?.运算符，这使得“深度空检查”变得轻而易举。详情请参见this+answer。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|322668|除了像this+deleted+answer建议的那样重新设计代码之外，另一个(尽管很糟糕)选择是使用try…catch块来查看在深度属性查找过程中是否出现了NullReferenceException。|322669|try
{
++++var+x+=+cake.frosting.berries.loader;
++++...
}
catch+(NullReferenceException+ex)
{
++++//+either+one+of+cake,+frosting,+or+berries+was+null
++++...
}|code-block|syntax|javascript|322670|出于以下原因，我个人不会这么做：|322671|322672|它看起来并不好。|unordered-list-item|322673|它使用异常处理，它应该针对异常情况，而不是你期望在operation.|322674|NullReferenceExceptions正常过程中经常发生的事情，可能永远不应该被显式地捕获。(请参阅this+question.)|322675|322676|322677|所以有没有可能使用某种扩展方法，或者它是一种语言特性，...|blockquote|322678|322679|322680|这几乎肯定是一种语言特性(在C#+6中以.?和?[]运算符的形式提供)，除非C#已经有了更复杂的惰性计算，或者除非您想使用反射(出于性能和类型安全的原因，这可能也不是一个好主意)。|322681|由于无法简单地将cake.frosting.berries.loader传递给函数(它将被求值并抛出空引用异常)，因此您必须以以下方式实现一个通用的查找方法:它接受一个对象和要查找的属性的名称：|322682|static+object+LookupProperty(+object+startingPoint,+params+string[]+lookupChain+)
{
++++//+1.+if+'startingPoint'+is+null,+return+null,+or+throw+an+exception.
++++//+2.+recursively+look+up+one+property/field+after+the+other+from+'lookupChain',
++++//++++using+reflection.
++++//+3.+if+one+lookup+is+not+possible,+return+null,+or+throw+an+exception.
++++//+3.+return+the+last+property/field's+value.
}

...

var+x+=+LookupProperty(+cake,+"frosting",+"berries",+"loader"+);|322683|(注:代码已编辑。)|322684|您很快就会发现这种方法存在几个问题。首先，您不会获得任何类型安全性，也不会对简单类型的属性值进行装箱。其次，如果出现问题，您可以返回null，然后必须在调用函数中进行检查，或者抛出异常，然后返回到开始的位置。第三，它可能会很慢。第四，它看起来比你一开始的样子更难看。|322685|322686|……，或者这只是个坏主意？|322687|322688|322689|我要么留下来：|322690|if+(cake+!=+null+&&+cake.frosting+!=+null+&&+...)+...|322691|或者采用Mehrdad的上述答案。|322692|322693|附言：回到我写这个答案的时候，我显然没有考虑lambda函数的表达式树；参见@driis‘answer获得这个方向的解决方案。它也基于一种反射，因此可能不如更简单的解决方案(if+(…+!=+null+&+…+!=+null)+…)那么好，但从语法的角度来看，它可能会更好。|322694|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/2081709/240733|1|https://stackoverflow.com/a/2080652/240733|2|https://stackoverflow.com/q/585480/240733^0|0|3|16|2|1Y|B|0|0|1F|9|27|M|3|J|1|0|0|0|0|0|0|0|M|1I|D|2|0|0|0|0|0|0|K|2|N|3|0|8|S|0|0|0|1U|4|0|0|0|0|0|0|0|0|0|0|3|2F|S|0^^$0|@$1|2|3|4|5|6|7|24|8|@$9|25|A|26|B|C]|$9|27|A|28|B|D]]|E|@$9|29|A|2A|1|2B]]|F|$]]|$1|G|3|H|5|6|7|2C|8|@$9|2D|A|2E|B|D]|$9|2F|A|2G|B|D]]|E|@$9|2H|A|2I|1|2J]]|F|$]]|$1|I|3|J|5|K|7|2K|8|@]|E|@]|F|$L|M]]|$1|N|3|O|5|6|7|2L|8|@]|E|@]|F|$]]|$1|P|3|-4|5|6|7|2M|8|@]|E|@]|F|$]]|$1|Q|3|R|5|S|7|2N|8|@]|E|@]|F|$]]|$1|T|3|U|5|S|7|2O|8|@]|E|@]|F|$]]|$1|V|3|W|5|S|7|2P|8|@$9|2Q|A|2R|B|D]]|E|@$9|2S|A|2T|1|2U]]|F|$]]|$1|X|3|-4|5|6|7|2V|8|@]|E|@]|F|$]]|$1|Y|3|-4|5|6|7|2W|8|@]|E|@]|F|$]]|$1|Z|3|10|5|11|7|2X|8|@]|E|@]|F|$]]|$1|12|3|-4|5|6|7|2Y|8|@]|E|@]|F|$]]|$1|13|3|-4|5|6|7|2Z|8|@]|E|@]|F|$]]|$1|14|3|15|5|6|7|30|8|@$9|31|A|32|B|D]|$9|33|A|34|B|D]]|E|@]|F|$]]|$1|16|3|17|5|6|7|35|8|@$9|36|A|37|B|D]]|E|@]|F|$]]|$1|18|3|19|5|K|7|38|8|@]|E|@]|F|$L|M]]|$1|1A|3|1B|5|6|7|39|8|@]|E|@]|F|$]]|$1|1C|3|1D|5|6|7|3A|8|@$9|3B|A|3C|B|D]]|E|@]|F|$]]|$1|1E|3|-4|5|6|7|3D|8|@]|E|@]|F|$]]|$1|1F|3|1G|5|11|7|3E|8|@]|E|@]|F|$]]|$1|1H|3|-4|5|6|7|3F|8|@]|E|@]|F|$]]|$1|1I|3|-4|5|6|7|3G|8|@]|E|@]|F|$]]|$1|1J|3|1K|5|6|7|3H|8|@]|E|@]|F|$]]|$1|1L|3|1M|5|K|7|3I|8|@]|E|@]|F|$L|M]]|$1|1N|3|1O|5|6|7|3J|8|@]|E|@]|F|$]]|$1|1P|3|-4|5|6|7|3K|8|@]|E|@]|F|$]]|$1|1Q|3|1R|5|6|7|3L|8|@$9|3M|A|3N|B|C]|$9|3O|A|3P|B|D]]|E|@]|F|$]]|$1|1S|3|-4|5|6|7|3Q|8|@]|E|@]|F|$]]]|1T|$1U|$5|1V|1W|1X|F|$1Y|1Z]]|20|$5|1V|1W|1X|F|$1Y|21]]|22|$5|1V|1W|1X|F|$1Y|23]]]]

Update: Starting with Visual Studio 2015, the C# compiler (language version 6) now recognizes the <code>?.</code> operator, which makes "deep null checking" a breeze. See <a href="https://stackoverflow.com/a/2081709/240733">this answer</a> for details.

Apart from re-designing your code, like 
<a href="https://stackoverflow.com/a/2080652/240733">this deleted answer</a> suggested,
another (albeit terrible) option would be to use a <code>try…catch</code> block to see if a <code>NullReferenceException</code> occurs sometime during that deep property lookup.

<pre><code>try
{
 var x = cake.frosting.berries.loader;
 ...
}
catch (NullReferenceException ex)
{
 // either one of cake, frosting, or berries was null
 ...
}
</code></pre>

I personally wouldn't do this for the following reasons:

<ul>
<li>It doesn't look nice.</li>
<li>It uses exception handling, which should target exceptional situations and not something that you expect to happen often during the normal course of operation.</li>
<li><code>NullReferenceException</code>s should probably never be caught explicitly. (See <a href="https://stackoverflow.com/q/585480/240733">this question</a>.)</li>
</ul>

<blockquote>
 So is it possible using some extension method or would it be a language feature, [...]
</blockquote>

This would almost certainly have to be a language feature (which is available in C# 6 in the form of the <code>.?</code> and <code>?[]</code> operators), unless C# already had more sophisticated lazy evaluation, or unless you want to use reflection (which probably also isn't a good idea for reasons of performance and type-safety).

Since there's no way to simply pass <code>cake.frosting.berries.loader</code> to a function (it would be evaluated and throw a null reference exception), you would have to implement a general look-up method in the following way: It takes in an objects and the names of properties to look up:

<pre><code>static object LookupProperty( object startingPoint, params string[] lookupChain )
{
 // 1. if 'startingPoint' is null, return null, or throw an exception.
 // 2. recursively look up one property/field after the other from 'lookupChain',
 // using reflection.
 // 3. if one lookup is not possible, return null, or throw an exception.
 // 3. return the last property/field's value.
}

...

var x = LookupProperty( cake, "frosting", "berries", "loader" );
</code></pre>

(Note: code edited.)

You quickly see several problems with such an approach. First, you don't get any type safety and possible boxing of property values of a simple type. Second, you can either return <code>null</code> if something goes wrong, and you will have to check for this in your calling function, or you throw an exception, and you're back to where you started. Third, it might be slow. Fourth, it looks uglier than what you started with.

<blockquote>
 [...], or is it just a bad idea?
</blockquote>

I'd either stay with:

<pre><code>if (cake != null &amp;&amp; cake.frosting != null &amp;&amp; ...) ...
</code></pre>

or go with the above answer by Mehrdad Afshari.

<hr>

P.S.: Back when I wrote this answer, I obviously didn't consider expression trees for lambda functions; see e.g. @driis' answer for a solution in this direction. It's also based on a kind of reflection and thus might not perform quite as well as a simpler solution (<code>if (… != null &amp; … != null) …</code>), but it may be judged nicer from a syntax point-of-view.

blocks|key|320727|text|我发现这个扩展对于深度嵌套的场景非常有用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|320728|public+static+R+Coal<T,+R>(this+T+obj,+Func<T,+R>+f)
++++where+T+:+class
{
++++return+obj+!=+null+?+f(obj)+:+default(R);
}|code-block|syntax|javascript|320729|这是我从C#和T-SQL中的null合并运算符衍生而来的想法。好的是返回类型总是内部属性的返回类型。|320730|这样你就可以这样做了：|320731|var+berries+=+cake.Coal(x+=>+x.frosting).Coal(x+=>+x.berries);|320732|...or是上述内容的一个细微变化：|320733|var+berries+=+cake.Coal(x+=>+x.frosting,+x+=>+x.berries);|320734|这不是我所知道的最好的语法，但它确实起作用了。|320735|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|X|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|Z|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|11|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

I've found this extension to be quite useful for deep nesting scenarios.

<pre><code>public static R Coal&lt;T, R&gt;(this T obj, Func&lt;T, R&gt; f)
 where T : class
{
 return obj != null ? f(obj) : default(R);
}
</code></pre>

It's an idea I derrived from the null coalescing operator in C# and T-SQL. The nice thing is that the return type is always the return type of the inner property.

That way you can do this:

<pre><code>var berries = cake.Coal(x =&gt; x.frosting).Coal(x =&gt; x.berries);
</code></pre>

...or a slight variation of the above:

<pre><code>var berries = cake.Coal(x =&gt; x.frosting, x =&gt; x.berries);
</code></pre>

It's not the best syntax I know, but it does work.

blocks|key|3281594|text|我们已经考虑添加一个新的操作“？”具有您想要的语义的语言。(现在已经添加了它；请参见下面的内容。)也就是说，你会说|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3281595|cake?.frosting?.berries?.loader|code-block|syntax|javascript|3281596|编译器会为你生成所有的短路检查。|3281597|它并没有成为C#+4的标准，也许是作为该语言假想的未来版本。|3281598|更新(2014):+?.运算符现在是下一个编译器版本的planned。请注意，对于操作符的确切语法和语义分析，仍然存在一些争论。|offset|length|style|BOLD|CODE|3281599|更新(+2015年7月)：+Visual+Studio2015已经发布，并附带了支持null-conditional+operators+?.+and+?[]的C#编译器。|3281600|entityMap|0|LINK|mutability|MUTABLE|url|https://roslyn.codeplex.com/wikipage?title=Language%2520Feature%2520Status&referringTitle=Documentation|1|https://msdn.microsoft.com/en-us/library/dn986595.aspx^0|0|0|0|0|0|9|L|17|A|2|R|7|0|0|0|2E|1X|2|24|3|16|11|1|0^^$0|@$1|2|3|4|5|6|7|13|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|14|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|15|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|16|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|17|8|@$M|18|N|19|O|P]|$M|1A|N|1B|O|P]|$M|1C|N|1D|O|Q]]|9|@$M|1E|N|1F|1|1G]]|A|$]]|$1|R|3|S|5|6|7|1H|8|@$M|1I|N|1J|O|P]|$M|1K|N|1L|O|Q]|$M|1M|N|1N|O|Q]]|9|@$M|1O|N|1P|1|1Q]]|A|$]]|$1|T|3|-4|5|6|7|1R|8|@]|9|@]|A|$]]]|U|$V|$5|W|X|Y|A|$Z|10]]|11|$5|W|X|Y|A|$Z|12]]]]

We have considered adding a new operation "?." to the language that has the semantics you want. (And it has been added now; see below.) That is, you'd say 

<pre><code>cake?.frosting?.berries?.loader
</code></pre>

and the compiler would generate all the short-circuiting checks for you.

It didn't make the bar for C# 4. Perhaps for a hypothetical future version of the language.

Update (2014):
 The <code>?.</code> operator is now <a href="https://roslyn.codeplex.com/wikipage?title=Language%20Feature%20Status&amp;referringTitle=Documentation" rel="noreferrer">planned</a> for the next Roslyn compiler release. Note that there is still some debate over the exact syntactic and semantic analysis of the operator.

Update (July 2015): Visual Studio 2015 has been released and ships with a C# compiler that supports the <a href="https://msdn.microsoft.com/en-us/library/dn986595.aspx" rel="noreferrer" title="MSDN reference page">null-conditional operators <code>?.</code> and <code>?[]</code></a>.

blocks|key|3281716|text|我受到这个问题的启发，试图找出如何通过使用表达式树的更简单/更漂亮的语法来完成这种深度空检查。虽然我确实同意这样的回答，即如果您经常需要访问层次结构中的深层实例，那么这可能是一个糟糕的设计，但我也确实认为在某些情况下，例如数据表示，它可能非常有用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3281717|所以我创建了一个扩展方法，它允许你写：|3281718|var+berries+=+cake.IfNotNull(c+=>+c.Frosting.Berries);|code-block|syntax|javascript|3281719|如果表达式没有任何部分为空，这将返回浆果。如果遇到null，则返回null。不过有一些需要注意的地方，在当前版本中，它只适用于简单的成员访问，而且它只适用于.NET+Framework4，因为它使用了v4中的新方法MemberExpression.Update。下面是IfNotNull扩展方法的代码：|3281720|using+System;
using+System.Collections.Generic;
using+System.Linq.Expressions;

namespace+dr.IfNotNullOperator.PoC
{
++++public+static+class+ObjectExtensions
++++{
++++++++public+static+TResult+IfNotNull<TArg,TResult>(this+TArg+arg,+Expression<Func<TArg,TResult>>+expression)
++++++++{
++++++++++++if+(expression+==+null)
++++++++++++++++throw+new+ArgumentNullException("expression");

++++++++++++if+(ReferenceEquals(arg,+null))
++++++++++++++++return+default(TResult);

++++++++++++var+stack+=+new+Stack<MemberExpression>();
++++++++++++var+expr+=+expression.Body+as+MemberExpression;
++++++++++++while(expr+!=+null)
++++++++++++{
++++++++++++++++stack.Push(expr);
++++++++++++++++expr+=+expr.Expression+as+MemberExpression;
++++++++++++}+

++++++++++++if+(stack.Count+==+0+%7C%7C+!(stack.Peek().Expression+is+ParameterExpression))
++++++++++++++++throw+new+ApplicationException(String.Format("The+expression+'{0}'+contains+unsupported+constructs.",
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++expression));

++++++++++++object+a+=+arg;
++++++++++++while(stack.Count+>+0)
++++++++++++{
++++++++++++++++expr+=+stack.Pop();
++++++++++++++++var+p+=+expr.Expression+as+ParameterExpression;
++++++++++++++++if+(p+==+null)
++++++++++++++++{
++++++++++++++++++++p+=+Expression.Parameter(a.GetType(),+"x");
++++++++++++++++++++expr+=+expr.Update(p);
++++++++++++++++}
++++++++++++++++var+lambda+=+Expression.Lambda(expr,+p);
++++++++++++++++Delegate+t+=+lambda.Compile();++++++++++++++++
++++++++++++++++a+=+t.DynamicInvoke(a);
++++++++++++++++if+(ReferenceEquals(a,+null))
++++++++++++++++++++return+default(TResult);
++++++++++++}

++++++++++++return+(TResult)a;++++++++++++
++++++++}
++++}
}|3281721|它的工作方式是检查表示表达式的表达式树，一个接一个地计算各个部分；每次检查结果是否不为空。|3281722|我相信这是可以扩展的，这样就可以支持MemberExpression以外的其他表达式。|3281723|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

I got inspired by this question to try and find out how this kind of deep null checking can be done with an easier / prettier syntax using expression trees. While I do agree with the answers stating that it might be a bad design if you often need to access instances deep in the hierarchy, I also do think that in some cases, such as data presentation, it can be very useful. 

So I created an extension method, that will allow you to write:

<pre><code>var berries = cake.IfNotNull(c =&gt; c.Frosting.Berries);
</code></pre>

This will return the Berries if no part of the expression is null. If null is encountered, null is returned. There are some caveats though, in the current version it will only work with simple member access, and it only works on .NET Framework 4, because it uses the MemberExpression.Update method, which is new in v4. This is the code for the IfNotNull extension method:

<pre><code>using System;
using System.Collections.Generic;
using System.Linq.Expressions;

namespace dr.IfNotNullOperator.PoC
{
 public static class ObjectExtensions
 {
 public static TResult IfNotNull&lt;TArg,TResult&gt;(this TArg arg, Expression&lt;Func&lt;TArg,TResult&gt;&gt; expression)
 {
 if (expression == null)
 throw new ArgumentNullException("expression");

 if (ReferenceEquals(arg, null))
 return default(TResult);

 var stack = new Stack&lt;MemberExpression&gt;();
 var expr = expression.Body as MemberExpression;
 while(expr != null)
 {
 stack.Push(expr);
 expr = expr.Expression as MemberExpression;
 } 

 if (stack.Count == 0 || !(stack.Peek().Expression is ParameterExpression))
 throw new ApplicationException(String.Format("The expression '{0}' contains unsupported constructs.",
 expression));

 object a = arg;
 while(stack.Count &gt; 0)
 {
 expr = stack.Pop();
 var p = expr.Expression as ParameterExpression;
 if (p == null)
 {
 p = Expression.Parameter(a.GetType(), "x");
 expr = expr.Update(p);
 }
 var lambda = Expression.Lambda(expr, p);
 Delegate t = lambda.Compile(); 
 a = t.DynamicInvoke(a);
 if (ReferenceEquals(a, null))
 return default(TResult);
 }

 return (TResult)a; 
 }
 }
}
</code></pre>

It works by examining the expression tree representing your expression, and evaluating the parts one after the other; each time checking that the result is not null. 

I am sure this could be extended so that other expressions than MemberExpression is supported. Consider this as proof-of-concept code, and please keep in mind that there will be a performance penalty by using it (which will probably not matter in many cases, but don't use it in a tight loop :-) )

blocks|key|3281730|text|一种选择是使用空对象模式，所以当你没有蛋糕时，你有一个返回NullFosting的NullCake，而不是Null。对不起，我不太擅长解释这一点，但其他人很擅长，请参阅|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3281731|3281732|An+example+of+the+Null+Object+Patten+usage|unordered-list-item|offset|length|3281733|The+wikipedai+write+up+on+the+Null+Object+Patten|3281734|3281735|entityMap|0|LINK|mutability|MUTABLE|url|http://www.codeguru.com/csharp/.net/net_general/patterns/article.php/c16503/|1|http://en.wikipedia.org/wiki/Null_Object_pattern^0|0|0|0|16|0|0|0|1C|1|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|V|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|W|8|@]|9|@$F|X|G|Y|1|Z]]|A|$]]|$1|H|3|I|5|E|7|10|8|@]|9|@$F|11|G|12|1|13]]|A|$]]|$1|J|3|-4|5|6|7|14|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]|S|$5|N|O|P|A|$Q|T]]]]

One option is to use the Null Object Patten, so instead of having null when you don’t have a cake, you have a NullCake that returns a NullFosting etc. Sorry I am not very good at explaining this but other people are, see

<ul>
<li><a href="http://www.codeguru.com/csharp/.net/net_general/patterns/article.php/c16503/" rel="nofollow noreferrer">An example of the Null Object Patten usage</a></li>
<li><a href="http://en.wikipedia.org/wiki/Null_Object_pattern" rel="nofollow noreferrer">The wikipedai write up on the Null Object Patten</a></li>
</ul>

blocks|key|3068789|text|我昨天晚上发了这个帖子，然后一个朋友给我指出了这个问题。希望能有所帮助。然后，您可以执行以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3068790|var+color+=+Dis.OrDat<string>(()+=>+cake.frosting.berries.color,+"blue");


using+System;
using+System.Collections.Generic;
using+System.Linq;
using+System.Text;
using+System.Linq.Expressions;

namespace+DeepNullCoalescence
{
++public+static+class+Dis
++{
++++public+static+T+OrDat<T>(Expression<Func><T>>+expr,+T+dat)
++++{
++++++try
++++++{
++++++++var+func+=+expr.Compile();
++++++++var+result+=+func.Invoke();
++++++++return+result+??+dat;+//now+we+can+coalesce
++++++}
++++++catch+(NullReferenceException)
++++++{
++++++++return+dat;
++++++}
++++}
++}
}|code-block|syntax|javascript|3068791|阅读full+blog+post+here。|offset|length|3068792|3068793|entityMap|0|LINK|mutability|MUTABLE|url|http://www.tsjensen.com/blog/2011/01/11/Deep%2BNull%2BCoalescing%2BIn%2BC%2BWith%2BDisOrDat.aspx^0|0|0|2|J|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|U|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|V|8|@]|9|@$I|W|J|X|1|Y]]|A|$]]|$1|K|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|10|8|@]|9|@]|A|$]]]|M|$N|$5|O|P|Q|A|$R|S]]]]

I posted this last night and then a friend pointed me to this question. Hope it helps. You can then do something like this:

<pre><code>var color = Dis.OrDat&lt;string&gt;(() =&gt; cake.frosting.berries.color, "blue");


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;

namespace DeepNullCoalescence
{
 public static class Dis
 {
 public static T OrDat&lt;T&gt;(Expression&lt;Func&gt;&lt;T&gt;&gt; expr, T dat)
 {
 try
 {
 var func = expr.Compile();
 var result = func.Invoke();
 return result ?? dat; //now we can coalesce
 }
 catch (NullReferenceException)
 {
 return dat;
 }
 }
 }
}
</code></pre>

Read the <a href="http://www.tsjensen.com/blog/2011/01/11/Deep+Null+Coalescing+In+C+With+DisOrDat.aspx" rel="nofollow">full blog post here</a>.

The same friend also suggested that you <a href="http://www.youtube.com/watch?v=kfJnqbudMzs&amp;feature=player_embedded#" rel="nofollow">watch this</a>.

blocks|key|3068811|text|虽然driis的答案很有趣，但我认为它在性能方面有点太昂贵了。与其编译许多委托，我更喜欢为每个属性路径编译一个lambda，缓存它，然后重新调用许多类型。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3068812|下面的NullCoalesce就是这样做的，它返回一个新的带有空检查的lambda表达式，并在任何路径为空的情况下返回默认值(TResult)。|3068813|示例：|3068814|NullCoalesce((Process+p)+=>+p.StartInfo.FileName)|code-block|syntax|javascript|3068815|将返回一个表达式|3068816|(Process+p)+=>+(p+!=+null+&&+p.StartInfo+!=+null+?+p.StartInfo.FileName+:+default(string));|3068817|代码：|3068818|++++static+void+Main(string[]+args)
++++{
++++++++var+converted+=+NullCoalesce((MethodInfo+p)+=>+p.DeclaringType.Assembly.Evidence.Locked);
++++++++var+converted2+=+NullCoalesce((string[]+s)+=>+s.Length);
++++}

++++private+static+Expression<Func<TSource,+TResult>>+NullCoalesce<TSource,+TResult>(Expression<Func<TSource,+TResult>>+lambdaExpression)
++++{
++++++++var+test+=+GetTest(lambdaExpression.Body);
++++++++if+(test+!=+null)
++++++++{
++++++++++++return+Expression.Lambda<Func<TSource,+TResult>>(
++++++++++++++++Expression.Condition(
++++++++++++++++++++test,
++++++++++++++++++++lambdaExpression.Body,
++++++++++++++++++++Expression.Default(
++++++++++++++++++++++++typeof(TResult)
++++++++++++++++++++)
++++++++++++++++),
++++++++++++++++lambdaExpression.Parameters
++++++++++++);
++++++++}
++++++++return+lambdaExpression;
++++}

++++private+static+Expression+GetTest(Expression+expression)
++++{
++++++++Expression+container;
++++++++switch+(expression.NodeType)
++++++++{
++++++++++++case+ExpressionType.ArrayLength:
++++++++++++++++container+=+((UnaryExpression)expression).Operand;
++++++++++++++++break;
++++++++++++case+ExpressionType.MemberAccess:
++++++++++++++++if+((container+=+((MemberExpression)expression).Expression)+==+null)
++++++++++++++++{
++++++++++++++++++++return+null;
++++++++++++++++}
++++++++++++++++break;
++++++++++++default:
++++++++++++++++return+null;
++++++++}
++++++++var+baseTest+=+GetTest(container);
++++++++if+(!container.Type.IsValueType)
++++++++{
++++++++++++var+containerNotNull+=+Expression.NotEqual(
++++++++++++++++container,
++++++++++++++++Expression.Default(
++++++++++++++++++++container.Type
++++++++++++++++)
++++++++++++);
++++++++++++return+(baseTest+==+null+?
++++++++++++++++containerNotNull+:
++++++++++++++++Expression.AndAlso(
++++++++++++++++++++baseTest,
++++++++++++++++++++containerNotNull
++++++++++++++++)
++++++++++++);
++++++++}
++++++++return+baseTest;
++++}|3068819|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|X|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|Y|8|@]|9|@]|A|$]]|$1|M|3|N|5|H|7|Z|8|@]|9|@]|A|$I|J]]|$1|O|3|P|5|6|7|10|8|@]|9|@]|A|$]]|$1|Q|3|R|5|H|7|11|8|@]|9|@]|A|$I|J]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

While driis' answer is interesting, I think it's a bit too expensive performance wise. Rather than compiling many delegates, I'd prefer to compile one lambda per property path, cache it and then reinvoke it many types.

NullCoalesce below does just that, it returns a new lambda expression with null checks and a return of default(TResult) in case any path is null.

Example:

<pre><code>NullCoalesce((Process p) =&gt; p.StartInfo.FileName)
</code></pre>

Will return an expression 

<pre><code>(Process p) =&gt; (p != null &amp;&amp; p.StartInfo != null ? p.StartInfo.FileName : default(string));
</code></pre>

Code:

<pre><code> static void Main(string[] args)
 {
 var converted = NullCoalesce((MethodInfo p) =&gt; p.DeclaringType.Assembly.Evidence.Locked);
 var converted2 = NullCoalesce((string[] s) =&gt; s.Length);
 }

 private static Expression&lt;Func&lt;TSource, TResult&gt;&gt; NullCoalesce&lt;TSource, TResult&gt;(Expression&lt;Func&lt;TSource, TResult&gt;&gt; lambdaExpression)
 {
 var test = GetTest(lambdaExpression.Body);
 if (test != null)
 {
 return Expression.Lambda&lt;Func&lt;TSource, TResult&gt;&gt;(
 Expression.Condition(
 test,
 lambdaExpression.Body,
 Expression.Default(
 typeof(TResult)
 )
 ),
 lambdaExpression.Parameters
 );
 }
 return lambdaExpression;
 }

 private static Expression GetTest(Expression expression)
 {
 Expression container;
 switch (expression.NodeType)
 {
 case ExpressionType.ArrayLength:
 container = ((UnaryExpression)expression).Operand;
 break;
 case ExpressionType.MemberAccess:
 if ((container = ((MemberExpression)expression).Expression) == null)
 {
 return null;
 }
 break;
 default:
 return null;
 }
 var baseTest = GetTest(container);
 if (!container.Type.IsValueType)
 {
 var containerNotNull = Expression.NotEqual(
 container,
 Expression.Default(
 container.Type
 )
 );
 return (baseTest == null ?
 containerNotNull :
 Expression.AndAlso(
 baseTest,
 containerNotNull
 )
 );
 }
 return baseTest;
 }
</code></pre>

blocks|key|3068930|text|我也经常希望有一个更简单的语法！当您的方法返回值可能为空时，它会变得特别难看，因为您需要额外的变量(例如：cake.frosting.flavors.FirstOrDefault().loader)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3068931|然而，我使用了一个相当不错的替代方法:创建一个Null-Safe-Chain帮助器方法。我意识到这与@John上面的答案非常相似(使用Coal扩展方法)，但我发现它更简单，输入更少。它看起来是这样的：|3068932|var+loader+=+NullSafe.Chain(cake,+c=>c.frosting,+f=>f.berries,+b=>b.loader);|code-block|syntax|javascript|3068933|下面是实现：|3068934|public+static+TResult+Chain<TA,TB,TC,TResult>(TA+a,+Func<TA,TB>+b,+Func<TB,TC>+c,+Func<TC,TResult>+r)+
where+TA:class+where+TB:class+where+TC:class+{
++++if+(a+==+null)+return+default(TResult);
++++var+B+=+b(a);
++++if+(B+==+null)+return+default(TResult);
++++var+C+=+c(B);
++++if+(C+==+null)+return+default(TResult);
++++return+r(C);
}|3068935|我还创建了几个重载(具有2到6个参数)，以及允许链以值类型或默认值结束的重载。这对我来说真的很好！|3068936|entityMap^0|1H|19|0|1V|4|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|10|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|11|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|12|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|13|8|@]|D|@]|E|$]]|$1|S|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|T|$]]

I too have often wished for a simpler syntax! It gets especially ugly when you have method-return-values that might be null, because then you need extra variables (for example: <code>cake.frosting.flavors.FirstOrDefault().loader</code>)

However, here's a pretty decent alternative that I use: create an Null-Safe-Chain helper method. I realize that this is pretty similar to @John's answer above (with the <code>Coal</code> extension method) but I find it's more straightforward and less typing. Here's what it looks like:

<pre><code>var loader = NullSafe.Chain(cake, c=&gt;c.frosting, f=&gt;f.berries, b=&gt;b.loader);
</code></pre>

Here's the implementation:

<pre><code>public static TResult Chain&lt;TA,TB,TC,TResult&gt;(TA a, Func&lt;TA,TB&gt; b, Func&lt;TB,TC&gt; c, Func&lt;TC,TResult&gt; r) 
where TA:class where TB:class where TC:class {
 if (a == null) return default(TResult);
 var B = b(a);
 if (B == null) return default(TResult);
 var C = c(B);
 if (C == null) return default(TResult);
 return r(C);
}
</code></pre>

I also created several overloads (with 2 to 6 parameters), as well as overloads that allow the chain to end with a value-type or default. This works really well for me!

blocks|key|3282019|text|尝试以下代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3282020|++++///+<summary>
++++///+check+deep+property
++++///+</summary>
++++///+<param+name="obj">instance</param>
++++///+<param+name="property">deep+property+not+include+instance+name+example+"A.B.C.D.E"</param>
++++///+<returns>if+null+return+true+else+return+false</returns>
++++public+static+bool+IsNull(this+object+obj,+string+property)
++++{
++++++++if+(string.IsNullOrEmpty(property)+%7C%7C+string.IsNullOrEmpty(property.Trim()))+throw+new+Exception("Parameter+:+property+is+empty");
++++++++if+(obj+!=+null)
++++++++{
++++++++++++string[]+deep+=+property.Split('.');
++++++++++++object+instance+=+obj;
++++++++++++Type+objType+=+instance.GetType();
++++++++++++PropertyInfo+propertyInfo;
++++++++++++foreach+(string+p+in+deep)
++++++++++++{
++++++++++++++++propertyInfo+=+objType.GetProperty(p);
++++++++++++++++if+(propertyInfo+==+null)+throw+new+Exception("No+property+:+"+%2B+p);
++++++++++++++++instance+=+propertyInfo.GetValue(instance,+null);
++++++++++++++++if+(instance+!=+null)
++++++++++++++++++++objType+=+instance.GetType();
++++++++++++++++else
++++++++++++++++++++return+true;
++++++++++++}
++++++++++++return+false;
++++++++}
++++++++else
++++++++++++return+true;
++++}|code-block|syntax|javascript|3282021|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|$]]

Try this code:

<pre><code> /// &lt;summary&gt;
 /// check deep property
 /// &lt;/summary&gt;
 /// &lt;param name="obj"&gt;instance&lt;/param&gt;
 /// &lt;param name="property"&gt;deep property not include instance name example "A.B.C.D.E"&lt;/param&gt;
 /// &lt;returns&gt;if null return true else return false&lt;/returns&gt;
 public static bool IsNull(this object obj, string property)
 {
 if (string.IsNullOrEmpty(property) || string.IsNullOrEmpty(property.Trim())) throw new Exception("Parameter : property is empty");
 if (obj != null)
 {
 string[] deep = property.Split('.');
 object instance = obj;
 Type objType = instance.GetType();
 PropertyInfo propertyInfo;
 foreach (string p in deep)
 {
 propertyInfo = objType.GetProperty(p);
 if (propertyInfo == null) throw new Exception("No property : " + p);
 instance = propertyInfo.GetValue(instance, null);
 if (instance != null)
 objType = instance.GetType();
 else
 return true;
 }
 return false;
 }
 else
 return true;
 }
</code></pre>

blocks|key|3068957|text|我稍微修改了here中的代码，使其适用于所提出的问题：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3068958|public+static+class+GetValueOrDefaultExtension
{
++++public+static+TResult+GetValueOrDefault<TSource,+TResult>(this+TSource+source,+Func<TSource,+TResult>+selector)
++++{
++++++++try+{+return+selector(source);+}
++++++++catch+{+return+default(TResult);+}
++++}
}|code-block|syntax|javascript|3068959|是的，由于尝试/捕获性能的影响，这可能不是最佳的解决方案，但它是有效的:>|3068960|用法：|3068961|var+val+=+cake.GetValueOrDefault(x+=>+x.frosting.berries.loader);|3068962|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/8132541/266659^0|6|4|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|11|8|@]|9|@]|C|$]]|$1|K|3|L|5|6|7|12|8|@]|9|@]|C|$]]|$1|M|3|N|5|F|7|13|8|@]|9|@]|C|$G|H]]|$1|O|3|-4|5|6|7|14|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]]]

I slightly modified the code from <a href="https://stackoverflow.com/a/8132541/266659">here</a> to make it work for the question asked:

<pre><code>public static class GetValueOrDefaultExtension
{
 public static TResult GetValueOrDefault&lt;TSource, TResult&gt;(this TSource source, Func&lt;TSource, TResult&gt; selector)
 {
 try { return selector(source); }
 catch { return default(TResult); }
 }
}
</code></pre>

And yes, this is probably not the optimal solution due to try/catch performance implications but it works :>

Usage:

<pre><code>var val = cake.GetValueOrDefault(x =&gt; x.frosting.berries.loader);
</code></pre>

blocks|key|3282063|text|对于C#中的深层表达式，有一个Maybe+codeplex+project使用lambda实现了可能或IfNotNull|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3282064|使用示例：|3282065|int?+CityId=+employee.Maybe(e=>e.Person.Address.City);|code-block|syntax|javascript|3282066|类似问题How+to+check+for+nulls+in+a+deep+lambda+expression?中的链接was+suggested|3282067|entityMap|0|LINK|mutability|MUTABLE|url|http://maybe.codeplex.com/|1|https://stackoverflow.com/questions/854591/how-to-check-for-nulls-in-a-deep-lambda-expression/|2|https://stackoverflow.com/a/2866634/52277^0|F|M|0|0|0|0|4|1F|1|1N|D|2|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@$A|Z|B|10|1|11]]|C|$]]|$1|D|3|E|5|6|7|12|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|13|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|14|8|@]|9|@$A|15|B|16|1|17]|$A|18|B|19|1|1A]]|C|$]]|$1|M|3|-4|5|6|7|1B|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]|W|$5|P|Q|R|C|$S|X]]]]

There is <a href="http://maybe.codeplex.com/" rel="nofollow noreferrer">Maybe codeplex project</a> that Implements 
Maybe or IfNotNull using lambdas for deep expressions in C#

Example of use:

<pre><code>int? CityId= employee.Maybe(e=&gt;e.Person.Address.City);
</code></pre>

The link <a href="https://stackoverflow.com/a/2866634/52277">was suggested</a> in a similar question <a href="https://stackoverflow.com/questions/854591/how-to-check-for-nulls-in-a-deep-lambda-expression/">How to check for nulls in a deep lambda expression?</a>

blocks|key|320967|text|我喜欢Objective-C所采取的方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|320968|“Objective-C语言采用了另一种方法来解决这个问题，它不会调用nil上的方法，而是为所有此类调用返回nil。”|320969|if+(cake.frosting.berries+!=+null)+
{
++++var+str+=+cake.frosting.berries...;
}|code-block|syntax|javascript|320970|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I like approach taken by Objective-C:

"The Objective-C language takes another approach to this problem and does not invoke methods on nil but instead returns nil for all such invocations." 

<pre><code>if (cake.frosting.berries != null) 
{
 var str = cake.frosting.berries...;
}
</code></pre>

blocks|key|3069128|text|正如John+Leidegren的answer中所建议的，解决这个问题的一种方法是使用扩展方法和委托。使用它们可能如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3069129|int?+numberOfBerries+=+cake
++++.NullOr(c+=>+c.Frosting)
++++.NullOr(f+=>+f.Berries)
++++.NullOr(b+=>+b.Count());|code-block|syntax|javascript|3069130|这个实现很混乱，因为你需要让它适用于值类型、引用类型和可为空的值类型。您可以在Timwi的answer+to+What+is+the+proper+way+to+check+for+null+values?中找到完整的实现。|3069131|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/users/58961/john-leidegren|1|https://stackoverflow.com/a/2080751/238753|2|https://stackoverflow.com/users/33225/timwi|3|https://stackoverflow.com/a/9825511/238753|4|https://stackoverflow.com/q/9788466/238753^0|2|E|0|H|6|1|0|0|13|5|2|19|6|3|1J|1C|4|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]|$A|14|B|15|1|16]]|C|$]]|$1|D|3|E|5|F|7|17|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|18|8|@]|9|@$A|19|B|1A|1|1B]|$A|1C|B|1D|1|1E]|$A|1F|B|1G|1|1H]]|C|$]]|$1|K|3|-4|5|6|7|1I|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]|S|$5|N|O|P|C|$Q|T]]|U|$5|N|O|P|C|$Q|V]]|W|$5|N|O|P|C|$Q|X]]|Y|$5|N|O|P|C|$Q|Z]]]]

As suggested in <a href="https://stackoverflow.com/users/58961/john-leidegren">John Leidegren</a>'s <a href="https://stackoverflow.com/a/2080751/238753">answer</a>, one approach to work-around this is to use extension methods and delegates. Using them could look something like this:

<pre><code>int? numberOfBerries = cake
 .NullOr(c =&gt; c.Frosting)
 .NullOr(f =&gt; f.Berries)
 .NullOr(b =&gt; b.Count());
</code></pre>

The implementation is messy because you need to get it to work for value types, reference types and nullable value types. You can find a complete implementation in <a href="https://stackoverflow.com/users/33225/timwi">Timwi</a>'s <a href="https://stackoverflow.com/a/9825511/238753">answer</a> to <a href="https://stackoverflow.com/q/9788466/238753">What is the proper way to check for null values?</a>.

blocks|key|321028|text|在您需要实现这一点的地方，执行以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|321029|用法|321030|Color+color+=+someOrder.ComplexGet(x+=>+x.Customer.LastOrder.Product.Color);|code-block|syntax|javascript|321031|或|321032|Color+color+=+Complex.Get(()+=>+someOrder.Customer.LastOrder.Product.Color);|321033|帮助器类实现|321034|public+static+class+Complex
{
++++public+static+T1+ComplexGet<T1,+T2>(this+T2+root,+Func<T2,+T1>+func)
++++{
++++++++return+Get(()+=>+func(root));
++++}

++++public+static+T+Get<T>(Func<T>+func)
++++{
++++++++try
++++++++{
++++++++++++return+func();
++++++++}
++++++++catch+(Exception)
++++++++{
++++++++++++return+default(T);
++++++++}
++++}
}|321035|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Where you need to achieve this, do this:

Usage

<pre><code>Color color = someOrder.ComplexGet(x =&gt; x.Customer.LastOrder.Product.Color);
</code></pre>

or

<pre><code>Color color = Complex.Get(() =&gt; someOrder.Customer.LastOrder.Product.Color);
</code></pre>

<h3>Helper class implementation</h3>

<pre><code>public static class Complex
{
 public static T1 ComplexGet&lt;T1, T2&gt;(this T2 root, Func&lt;T2, T1&gt; func)
 {
 return Get(() =&gt; func(root));
 }

 public static T Get&lt;T&gt;(Func&lt;T&gt; func)
 {
 try
 {
 return func();
 }
 catch (Exception)
 {
 return default(T);
 }
 }
}
</code></pre>

blocks|key|321038|text|或者您可以使用反射:)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|321039|反射函数：|321040|public+Object+GetPropValue(String+name,+Object+obj)
++++{
++++++++foreach+(String+part+in+name.Split('.'))
++++++++{
++++++++++++if+(obj+==+null)+{+return+null;+}

++++++++++++Type+type+=+obj.GetType();
++++++++++++PropertyInfo+info+=+type.GetProperty(part);
++++++++++++if+(info+==+null)+{+return+null;+}

++++++++++++obj+=+info.GetValue(obj,+null);
++++++++}
++++++++return+obj;
++++}|code-block|syntax|javascript|321041|用法：|321042|object+test1+=+GetPropValue("PropertyA.PropertyB.PropertyC",obj);|321043|我的情况(在反射函数中返回DBNull.Value而不是null+)：|321044|cmd.Parameters.AddWithValue("CustomerContactEmail",+GetPropValue("AccountingCustomerParty.Party.Contact.ElectronicMail.Value",+eInvoiceType));|321045|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Or you may use reflection :)

Reflection function:

<pre><code>public Object GetPropValue(String name, Object obj)
 {
 foreach (String part in name.Split('.'))
 {
 if (obj == null) { return null; }

 Type type = obj.GetType();
 PropertyInfo info = type.GetProperty(part);
 if (info == null) { return null; }

 obj = info.GetValue(obj, null);
 }
 return obj;
 }
</code></pre>

Usage: 

<pre><code>object test1 = GetPropValue("PropertyA.PropertyB.PropertyC",obj);
</code></pre>

My Case(return DBNull.Value instead of null in reflection function):

<pre><code>cmd.Parameters.AddWithValue("CustomerContactEmail", GetPropValue("AccountingCustomerParty.Party.Contact.ElectronicMail.Value", eInvoiceType));
</code></pre>

Note: This question was asked before the introduction of <a href="https://msdn.microsoft.com/en-us/library/dn986595.aspx" rel="noreferrer">the <code>.?</code> operator in C# 6 / Visual Studio 2015</a>.

We've all been there, we have some deep property like cake.frosting.berries.loader that we need to check if it's null so there's no exception. The way to do is is to use a short-circuiting if statement

<pre><code>if (cake != null &amp;&amp; cake.frosting != null &amp;&amp; cake.frosting.berries != null) ...
</code></pre>

This is not exactly elegant, and there should perhaps be an easier way to check the entire chain and see if it comes up against a null variable/property. 

Is it possible using some extension method or would it be a language feature, or is it just a bad idea?

Deep null checking, is there a better way?

Visual Studio

语义分析

Objective-C

编译器

注意：这个问题是在引入之前提出的。我们都遇到过这样的情况，我们有一些像cake.frosting.berries.loader这样的深层属性，我们需要检查它是否为空，所以没有异常。这样做的方法是使用短路if语句if (cake != null && cake.frosting != null && cake.frost...

问深度空检查，有没有更好的方法？
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问深度空检查，有没有更好的方法？
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