blocks|key|1935314|text|我将使用与Nullable类型类似的模式，在PropertyA类型中编写自己的方法(如果不是您的类型，则编写扩展方法)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1935315|class+PropertyAType
{
+++public+PropertyBType+PropertyB+{get;+set;+}

+++public+PropertyBType+GetPropertyBOrDefault()
+++{
+++++++return+PropertyB+!=+null+?+PropertyB+:+defaultValue;
+++}
}|code-block|syntax|javascript|1935316|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 would write your own method in the type of PropertyA (or an extension method if it's not your type) using the similar pattern to the Nullable type.

<pre><code>class PropertyAType
{
 public PropertyBType PropertyB {get; set; }

 public PropertyBType GetPropertyBOrDefault()
 {
 return PropertyB != null ? PropertyB : defaultValue;
 }
}
</code></pre>

blocks|key|383077|text|你这样做是对的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|383078|您可以使用类似于这里描述的技巧，使用Linq表达式：|offset|length|383079|int+value+=+ObjectA.NullSafeEval(x+=>+x.PropertyA.PropertyB.PropertyC,+0);|code-block|syntax|javascript|383080|但是手动检查每个属性要慢得多.|383081|entityMap|0|LINK|mutability|MUTABLE|url|http://www.thomaslevesque.com/2010/02/21/automating-null-checks-with-linq-expressions/^0|0|8|2|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@$D|W|E|X|1|Y]]|A|$]]|$1|F|3|G|5|H|7|Z|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

The way you're doing it is correct.

You could use a trick like the one described <a href="http://www.thomaslevesque.com/2010/02/21/automating-null-checks-with-linq-expressions/" rel="noreferrer">here</a>, using Linq expressions :

<pre><code>int value = ObjectA.NullSafeEval(x =&gt; x.PropertyA.PropertyB.PropertyC, 0);
</code></pre>

But it's much slower that manually checking each property...

blocks|key|1935362|text|这是不可能的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1935363|如果由于空取消引用导致ObjectA.PropertyA.PropertyB为null，则ObjectA将失败，这是一个错误。|offset|length|style|CODE|1935364|if(ObjectA+!=+null+&&+ObjectA.PropertyA+...由于短路而产生的工作(+ObjectA.PropertyA将永远不会检查ObjectA是否为null+)。|1935365|你提出的第一种方式是最好和最明确的意图。如果有的话，你可以尝试重新设计，而不必依赖如此多的空。|1935366|entityMap^0|0|B|R|19|7|0|0|13|1J|H|27|7|2H|4|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@$D|P|E|Q|F|G]|$D|R|E|S|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|T|8|@$D|U|E|V|F|G]|$D|W|E|X|F|G]|$D|Y|E|Z|F|G]|$D|10|E|11|F|G]]|9|@]|A|$]]|$1|J|3|K|5|6|7|12|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|M|$]]

It is not possible. 
<code>ObjectA.PropertyA.PropertyB</code> will fail if <code>ObjectA</code> is null due to null dereferencing, which is an error.

<code>if(ObjectA != null &amp;&amp; ObjectA.PropertyA</code> ... works due to short circuiting, ie <code>ObjectA.PropertyA</code> will never be checked if <code>ObjectA</code> is <code>null</code>.

The first way you propose is the best and most clear with intent. If anything you could try to redesign without having to rely on so many nulls.

blocks|key|383176|text|该代码是“最少数量的代码”，但不是最佳实践：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|383177|try
{
++++return+ObjectA.PropertyA.PropertyB.PropertyC;
}
catch(NullReferenceException)
{
+++++return+null;
}|code-block|syntax|javascript|383178|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|$]]

This code is "the least amount of code", but not the best practice:

<pre><code>try
{
 return ObjectA.PropertyA.PropertyB.PropertyC;
}
catch(NullReferenceException)
{
 return null;
}
</code></pre>

blocks|key|383189|text|你能给你的班级添加一个方法吗？如果没有，您考虑过使用扩展方法吗？您可以为对象类型创建一个名为GetPropC()的扩展方法。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|383190|示例：|383191|public+static+class+MyExtensions
{
++++public+static+int+GetPropC(this+MyObjectType+obj,+int+defaltValue)
++++{
++++++++if+(obj+!=+null+&&+obj.PropertyA+!=+null+&+obj.PropertyA.PropertyB+!=+null)
++++++++++++return+obj.PropertyA.PropertyB.PropertyC;
++++++++return+defaltValue;
++++}
}|code-block|syntax|javascript|383192|用法：|383193|int+val+=+ObjectA.GetPropC(0);+//+will+return+PropC+value,+or+0+(defaltValue)|383194|顺便说一下，这假设您使用的是.NET+3或更高版本。|383195|entityMap^0|1A|A|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|Y|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|Z|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|10|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|11|8|@]|D|@]|E|$]]|$1|S|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|T|$]]

Can you add a method to your class? If not, have you thought about using extension methods? You could create an extension method for your object type called <code>GetPropC()</code>.

Example:

<pre><code>public static class MyExtensions
{
 public static int GetPropC(this MyObjectType obj, int defaltValue)
 {
 if (obj != null &amp;&amp; obj.PropertyA != null &amp; obj.PropertyA.PropertyB != null)
 return obj.PropertyA.PropertyB.PropertyC;
 return defaltValue;
 }
}
</code></pre>

Usage:

<pre><code>int val = ObjectA.GetPropC(0); // will return PropC value, or 0 (defaltValue)
</code></pre>

By the way, this assumes you are using .NET 3 or higher.

blocks|key|383204|text|你可以这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|383205|class+ObjectAType
{
++++public+int+PropertyC
++++{
++++++++get
++++++++{
++++++++++++if+(PropertyA+==+null)
++++++++++++++++return+0;
++++++++++++if+(PropertyA.PropertyB+==+null)
++++++++++++++++return+0;
++++++++++++return+PropertyA.PropertyB.PropertyC;
++++++++}
++++}
}



if+(ObjectA+!=+null)
{
++++int+value+=+ObjectA.PropertyC;
++++...
}|code-block|syntax|javascript|383206|或者更好的可能是：|383207|private+static+int+GetPropertyC(ObjectAType+objectA)
{
++++if+(objectA+==+null)
++++++++return+0;
++++if+(objectA.PropertyA+==+null)
++++++++return+0;
++++if+(objectA.PropertyA.PropertyB+==+null)
++++++++return+0;
++++return+objectA.PropertyA.PropertyB.PropertyC;
}


int+value+=+GetPropertyC(ObjectA);|383208|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|$]]

You could do this:

<pre><code>class ObjectAType
{
 public int PropertyC
 {
 get
 {
 if (PropertyA == null)
 return 0;
 if (PropertyA.PropertyB == null)
 return 0;
 return PropertyA.PropertyB.PropertyC;
 }
 }
}



if (ObjectA != null)
{
 int value = ObjectA.PropertyC;
 ...
}
</code></pre>

Or even better might be this:

<pre><code>private static int GetPropertyC(ObjectAType objectA)
{
 if (objectA == null)
 return 0;
 if (objectA.PropertyA == null)
 return 0;
 if (objectA.PropertyA.PropertyB == null)
 return 0;
 return objectA.PropertyA.PropertyB.PropertyC;
}


int value = GetPropertyC(ObjectA);
</code></pre>

blocks|key|1935445|text|重构观察德米特定律|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1935446|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Law_of_Demeter^0|4|5|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

Refactor to observe the <a href="http://en.wikipedia.org/wiki/Law_of_Demeter" rel="noreferrer">Law of Demeter</a>

blocks|key|383254|text|假设您有类型的空值，一种方法是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|383255|var+x+=+(((objectA+??+A.Empty).PropertyOfB+??+B.Empty).PropertyOfC+??+C.Empty).PropertyOfString;|code-block|syntax|javascript|383256|我是C#的忠实粉丝，但在新Java+(1.7?)中却是一个非常好的东西。是.+.？接线员：|383257|+var+x+=+objectA.?PropertyOfB.?PropertyOfC.?PropertyOfString;|383258|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|$]]

Assuming you have empty values of types one approach would be this:

<pre><code>var x = (((objectA ?? A.Empty).PropertyOfB ?? B.Empty).PropertyOfC ?? C.Empty).PropertyOfString;
</code></pre>

I'm a big fan of C# but a very nice thing in new Java (1.7?) is the .? operator:

<pre><code> var x = objectA.?PropertyOfB.?PropertyOfC.?PropertyOfString;
</code></pre>

blocks|key|383268|text|您显然是在寻找可空Monad|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|383269|string+result+=+new+A().PropertyB.PropertyC.Value;|code-block|syntax|javascript|383270|变成了|383271|string+result+=+from+a+in+new+A()
++++++++++++++++from+b+in+a.PropertyB
++++++++++++++++from+c+in+b.PropertyC
++++++++++++++++select+c.Value;|383272|如果任何可为空的属性为空，则返回null；否则返回Value的值。|CODE|383273|class+A+{+public+B+PropertyB+{+get;+set;+}+}
class+B+{+public+C+PropertyC+{+get;+set;+}+}
class+C+{+public+string+Value+{+get;+set;+}+}|383274|LINQ扩展方法：|383275|public+static+class+NullableExtensions
{
++++public+static+TResult+SelectMany<TOuter,+TInner,+TResult>(
++++++++this+TOuter+source,
++++++++Func<TOuter,+TInner>+innerSelector,
++++++++Func<TOuter,+TInner,+TResult>+resultSelector)
++++++++where+TOuter+:+class
++++++++where+TInner+:+class
++++++++where+TResult+:+class
++++{
++++++++if+(source+==+null)+return+null;
++++++++TInner+inner+=+innerSelector(source);
++++++++if+(inner+==+null)+return+null;
++++++++return+resultSelector(source,+inner);
++++}
}|383276|entityMap^0|7|7|0|0|0|0|G|4|P|5|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@$9|10|A|11|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|12|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|13|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|14|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|15|8|@$9|16|A|17|B|Q]|$9|18|A|19|B|Q]]|D|@]|E|$]]|$1|R|3|S|5|H|7|1A|8|@]|D|@]|E|$I|J]]|$1|T|3|U|5|6|7|1B|8|@]|D|@]|E|$]]|$1|V|3|W|5|H|7|1C|8|@]|D|@]|E|$I|J]]|$1|X|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|Y|$]]

You're obviously looking for the Nullable Monad:

<pre><code>string result = new A().PropertyB.PropertyC.Value;
</code></pre>

becomes

<pre><code>string result = from a in new A()
 from b in a.PropertyB
 from c in b.PropertyC
 select c.Value;
</code></pre>

This returns <code>null</code>, if any of the nullable properties are null; otherwise, the value of <code>Value</code>.

<pre><code>class A { public B PropertyB { get; set; } }
class B { public C PropertyC { get; set; } }
class C { public string Value { get; set; } }
</code></pre>

<hr>

LINQ extension methods:

<pre><code>public static class NullableExtensions
{
 public static TResult SelectMany&lt;TOuter, TInner, TResult&gt;(
 this TOuter source,
 Func&lt;TOuter, TInner&gt; innerSelector,
 Func&lt;TOuter, TInner, TResult&gt; resultSelector)
 where TOuter : class
 where TInner : class
 where TResult : class
 {
 if (source == null) return null;
 TInner inner = innerSelector(source);
 if (inner == null) return null;
 return resultSelector(source, inner);
 }
}
</code></pre>

blocks|key|1580184|text|一旦你克服了“朗伯达”的“粘糊糊”，这种方法就相当直截了当：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1580185|public+static+TProperty+GetPropertyOrDefault<TObject,+TProperty>(this+TObject+model,+Func<TObject,+TProperty>+valueFunc)++
++++++++++++++++++++++++++++++++++++++++++++++++++++++++where+TObject+:+class
++++{
++++++++try
++++++++{
++++++++++++return+valueFunc.Invoke(model);
++++++++}
++++++++catch+(NullReferenceException+nex)
++++++++{
++++++++++++return+default(TProperty);
++++++++}
++++}|code-block|syntax|javascript|1580186|它的用法类似于：|1580187|ObjectA+objectA+=+null;

Assert.AreEqual(0,objectA.GetPropertyOrDefault(prop=>prop.ObjectB.ObjectB.ObjectC.ID));

Assert.IsNull(objectA.GetPropertyOrDefault(prop+=>+prop.ObjectB));|1580188|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|$]]

This approach is fairly straight-forward once you get over the lambda gobbly-gook:

<pre><code>public static TProperty GetPropertyOrDefault&lt;TObject, TProperty&gt;(this TObject model, Func&lt;TObject, TProperty&gt; valueFunc) 
 where TObject : class
 {
 try
 {
 return valueFunc.Invoke(model);
 }
 catch (NullReferenceException nex)
 {
 return default(TProperty);
 }
 }
</code></pre>

With usage that might look like:

<pre><code>ObjectA objectA = null;

Assert.AreEqual(0,objectA.GetPropertyOrDefault(prop=&gt;prop.ObjectB.ObjectB.ObjectC.ID));

Assert.IsNull(objectA.GetPropertyOrDefault(prop =&gt; prop.ObjectB));
</code></pre>

blocks|key|1580192|text|var+result+=+nullableproperty+??+defaultvalue;|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1580193|??+(空合并运算符)意味着如果第一个参数是null，则返回第二个参数。|unstyled|offset|length|style|CODE|1580194|entityMap^0|0|0|2|M|4|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|N|8|@$G|O|H|P|I|J]|$G|Q|H|R|I|J]]|9|@]|A|$]]|$1|K|3|-4|5|F|7|S|8|@]|9|@]|A|$]]]|L|$]]

<pre><code>var result = nullableproperty ?? defaultvalue;
</code></pre>

The <code>??</code> (null-coalescing operator) means if the first argument is <code>null</code>, return the second one instead.

blocks|key|1935587|text|当我需要链接这样的调用时，我依赖于我创建的助手方法TryGet()：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1935588|++++public+static+U+TryGet<T,+U>(this+T+obj,+Func<T,+U>+func)
++++{
++++++++return+obj.TryGet(func,+default(U));
++++}

++++public+static+U+TryGet<T,+U>(this+T+obj,+Func<T,+U>+func,+U+whenNull)
++++{
++++++++return+obj+==+null+?+whenNull+:+func(obj);
++++}|code-block|syntax|javascript|1935589|在您的例子中，您可以这样使用它：|1935590|++++int+value+=+ObjectA
++++++++.TryGet(p+=>+p.PropertyA)
++++++++.TryGet(p+=>+p.PropertyB)
++++++++.TryGet(p+=>+p.PropertyC,+defaultVal);|1935591|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|$]]

When I need to chain calls like that, I rely on a helper method I created, TryGet():

<pre><code> public static U TryGet&lt;T, U&gt;(this T obj, Func&lt;T, U&gt; func)
 {
 return obj.TryGet(func, default(U));
 }

 public static U TryGet&lt;T, U&gt;(this T obj, Func&lt;T, U&gt; func, U whenNull)
 {
 return obj == null ? whenNull : func(obj);
 }
</code></pre>

In your case, you would use it like so:

<pre><code> int value = ObjectA
 .TryGet(p =&gt; p.PropertyA)
 .TryGet(p =&gt; p.PropertyB)
 .TryGet(p =&gt; p.PropertyC, defaultVal);
</code></pre>

blocks|key|1935600|text|只是在这个帖子上绊倒了。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1935601|不久前，我就Visual提出了关于添加一个新的???操作符的建议。|offset|length|style|CODE|1935602|http://visualstudio.uservoice.com/forums/121579-visual-studio/suggestions/4104392-add-as-an-recursive-null-reference-check-opera|1935603|这将需要框架团队的一些工作，但不需要改变语言，而只需要做一些编译器魔术。这个想法是编译器应该修改这个代码(语法不允许atm)。|1935604|string+product_name+=+Order.OrderDetails[0].Product.Name+???+"no+product+defined";|code-block|syntax|javascript|1935605|转到这个代码中|1935606|Func<string>+_get_default+=+()+=>+"no+product+defined";+
string+product_name+=+Order+==+null+
++++?+_get_default.Invoke()+
++++:+Order.OrderDetails[0]+==+null+
++++++++?+_get_default.Invoke()+
++++++++:+Order.OrderDetails[0].Product+==+null+
++++++++++++?+_get_default.Invoke()+
++++++++++++:+Order.OrderDetails[0].Product.Name+??+_get_default.Invoke()|1935607|对于空检查，这可能如下所示|1935608|bool+isNull+=+(Order.OrderDetails[0].Product+???+null)+==+null;|1935609|entityMap|0|LINK|mutability|MUTABLE|url^0|0|N|3|0|0|3K|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|15|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|16|8|@$D|17|E|18|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|19|8|@]|9|@$D|1A|E|1B|1|1C]]|A|$]]|$1|J|3|K|5|6|7|1D|8|@]|9|@]|A|$]]|$1|L|3|M|5|N|7|1E|8|@]|9|@]|A|$O|P]]|$1|Q|3|R|5|6|7|1F|8|@]|9|@]|A|$]]|$1|S|3|T|5|N|7|1G|8|@]|9|@]|A|$O|P]]|$1|U|3|V|5|6|7|1H|8|@]|9|@]|A|$]]|$1|W|3|X|5|N|7|1I|8|@]|9|@]|A|$O|P]]|$1|Y|3|-4|5|6|7|1J|8|@]|9|@]|A|$]]]|Z|$10|$5|11|12|13|A|$14|I]]]]

Just stumbled accross this post.

Some time ago I made a suggestion on Visual Studio Connect about adding a new <code>???</code> operator.

<a href="http://visualstudio.uservoice.com/forums/121579-visual-studio/suggestions/4104392-add-as-an-recursive-null-reference-check-opera" rel="nofollow">http://visualstudio.uservoice.com/forums/121579-visual-studio/suggestions/4104392-add-as-an-recursive-null-reference-check-opera</a>

This would require some work from the framework team but don't need to alter the language but just do some compiler magic. The idea was that the compiler should change this code (syntax not allowed atm)

<pre><code>string product_name = Order.OrderDetails[0].Product.Name ??? "no product defined";
</code></pre>

into this code

<pre><code>Func&lt;string&gt; _get_default = () =&gt; "no product defined"; 
string product_name = Order == null 
 ? _get_default.Invoke() 
 : Order.OrderDetails[0] == null 
 ? _get_default.Invoke() 
 : Order.OrderDetails[0].Product == null 
 ? _get_default.Invoke() 
 : Order.OrderDetails[0].Product.Name ?? _get_default.Invoke()
</code></pre>

For null check this could look like

<pre><code>bool isNull = (Order.OrderDetails[0].Product ??? null) == null;
</code></pre>

blocks|key|1935616|text|您可以使用以下扩展，我认为它非常好：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1935617|///+<summary>
///+Simplifies+null+checking
///+</summary>
public+static+TR+Get<TF,+TR>(TF+t,+Func<TF,+TR>+f)
++++where+TF+:+class
{
++++return+t+!=+null+?+f(t)+:+default(TR);
}

///+<summary>
///+Simplifies+null+checking
///+</summary>
public+static+TR+Get<T1,+T2,+TR>(T1+p1,+Func<T1,+T2>+p2,+Func<T2,+TR>+p3)
++++where+T1+:+class
++++where+T2+:+class
{
++++return+Get(Get(p1,+p2),+p3);
}

///+<summary>
///+Simplifies+null+checking
///+</summary>
public+static+TR+Get<T1,+T2,+T3,+TR>(T1+p1,+Func<T1,+T2>+p2,+Func<T2,+T3>+p3,+Func<T3,+TR>+p4)
++++where+T1+:+class
++++where+T2+:+class
++++where+T3+:+class
{
++++return+Get(Get(Get(p1,+p2),+p3),+p4);
}|code-block|syntax|javascript|1935618|它是这样使用的：|1935619|int+value+=+Nulify.Get(objectA,+x=>x.PropertyA,+x=>x.PropertyB,+x=>x.PropertyC);|1935620|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|$]]

you can use the following extension and I think it is really good:

<pre><code>/// &lt;summary&gt;
/// Simplifies null checking
/// &lt;/summary&gt;
public static TR Get&lt;TF, TR&gt;(TF t, Func&lt;TF, TR&gt; f)
 where TF : class
{
 return t != null ? f(t) : default(TR);
}

/// &lt;summary&gt;
/// Simplifies null checking
/// &lt;/summary&gt;
public static TR Get&lt;T1, T2, TR&gt;(T1 p1, Func&lt;T1, T2&gt; p2, Func&lt;T2, TR&gt; p3)
 where T1 : class
 where T2 : class
{
 return Get(Get(p1, p2), p3);
}

/// &lt;summary&gt;
/// Simplifies null checking
/// &lt;/summary&gt;
public static TR Get&lt;T1, T2, T3, TR&gt;(T1 p1, Func&lt;T1, T2&gt; p2, Func&lt;T2, T3&gt; p3, Func&lt;T3, TR&gt; p4)
 where T1 : class
 where T2 : class
 where T3 : class
{
 return Get(Get(Get(p1, p2), p3), p4);
}
</code></pre>

And it is used like this:

<pre><code>int value = Nulify.Get(objectA, x=&gt;x.PropertyA, x=&gt;x.PropertyB, x=&gt;x.PropertyC);
</code></pre>

blocks|key|1935625|text|短扩展法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1935626|public+static+TResult+IfNotNull<TInput,+TResult>(this+TInput+o,+Func<TInput,+TResult>+evaluator)
++where+TResult+:+class+where+TInput+:+class
{
++if+(o+==+null)+return+null;
++return+evaluator(o);
}|code-block|syntax|javascript|1935627|使用|1935628|PropertyC+value+=+ObjectA.IfNotNull(x+=>+x.PropertyA).IfNotNull(x+=>+x.PropertyB).IfNotNull(x+=>+x.PropertyC);|1935629|这种简单的扩展方法以及在http://devtalk.net/csharp/chained-null-checks-and-the-maybe-monad/上可以找到的更多内容|offset|length|1935630|编辑：|1935631|在使用它片刻之后，我认为这个方法的正确名称应该是IfNotNull()，而不是原来的With()。|style|BOLD|1935632|entityMap|0|LINK|mutability|MUTABLE|url|http://devtalk.net/csharp/chained-null-checks-and-the-maybe-monad/^0|0|0|0|0|C|1U|0|0|0|O|B|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|14|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|16|8|@]|9|@$M|17|N|18|1|19]]|A|$]]|$1|O|3|P|5|6|7|1A|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1B|8|@$M|1C|N|1D|S|T]]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]]]

Short Extension Method:

<pre><code>public static TResult IfNotNull&lt;TInput, TResult&gt;(this TInput o, Func&lt;TInput, TResult&gt; evaluator)
 where TResult : class where TInput : class
{
 if (o == null) return null;
 return evaluator(o);
}
</code></pre>

Using

<pre><code>PropertyC value = ObjectA.IfNotNull(x =&gt; x.PropertyA).IfNotNull(x =&gt; x.PropertyB).IfNotNull(x =&gt; x.PropertyC);
</code></pre>

This simple extension method and much more you can find on <a href="http://devtalk.net/csharp/chained-null-checks-and-the-maybe-monad/">http://devtalk.net/csharp/chained-null-checks-and-the-maybe-monad/</a>

EDIT:

After using it for moment I think the proper name for this method should be IfNotNull() instead of original With().

blocks|key|1580257|text|2014年更新:+C#+6有一个名为“安全导航”或“空传播”的新操作符?.|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1580258|parent?.child|code-block|syntax|javascript|1580259|详细信息请阅读http://blogs.msdn.com/b/jerrynixon/archive/2014/02/26/at-last-c-is-getting-sometimes-called-the-safe-navigation-operator.aspx|1580260|这一直是一个非常受欢迎的请求code=594c10a522f8e9bc987ee4a5e2c0b38d。|1580261|entityMap|0|LINK|mutability|MUTABLE|url|http://blogs.msdn.com/b/jerrynixon/archive/2014/02/26/at-last-c-is-getting-sometimes-called-the-safe-navigation-operator.aspx|1|https://visualstudio.uservoice.com/forums/121579-visual-studio/suggestions/3990187-add-operator-to-c-?tracking_code=594c10a522f8e9bc987ee4a5e2c0b38d^0|Z|2|0|0|7|3H|0|0|E|11|1|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|12|8|@]|D|@$9|13|A|14|1|15]]|E|$]]|$1|M|3|N|5|6|7|16|8|@]|D|@$9|17|A|18|1|19]]|E|$]]|$1|O|3|-4|5|6|7|1A|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]|W|$5|R|S|T|E|$U|X]]]]

Update 2014: C# 6 has a new operator <code>?.</code> various called 'safe navigation' or 'null propagating'

<pre><code>parent?.child
</code></pre>

Read <a href="http://blogs.msdn.com/b/jerrynixon/archive/2014/02/26/at-last-c-is-getting-sometimes-called-the-safe-navigation-operator.aspx">http://blogs.msdn.com/b/jerrynixon/archive/2014/02/26/at-last-c-is-getting-sometimes-called-the-safe-navigation-operator.aspx</a> for details

This has long been a hugely popular request 
<a href="https://visualstudio.uservoice.com/forums/121579-visual-studio/suggestions/3990187-add-operator-to-c-?tracking_code=594c10a522f8e9bc987ee4a5e2c0b38d">https://visualstudio.uservoice.com/forums/121579-visual-studio/suggestions/3990187-add-operator-to-c-?tracking_code=594c10a522f8e9bc987ee4a5e2c0b38d</a>

blocks|key|1935677|text|我编写了一个接受默认值的方法，下面是如何使用它：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1935678|var+teacher+=+new+Teacher();
return+teacher.GetProperty(t+=>+t.Name);
return+teacher.GetProperty(t+=>+t.Name,+"Default+name");|code-block|syntax|javascript|1935679|以下是代码：|1935680|public+static+class+Helper
{
++++///+<summary>
++++///+Gets+a+property+if+the+object+is+not+null.
++++///+var+teacher+=+new+Teacher();
++++///+return+teacher.GetProperty(t+=>+t.Name);
++++///+return+teacher.GetProperty(t+=>+t.Name,+"Default+name");
++++///+</summary>
++++public+static+TSecond+GetProperty<TFirst,+TSecond>(this+TFirst+item1,
++++++++Func<TFirst,+TSecond>+getItem2,+TSecond+defaultValue+=+default(TSecond))
++++{
++++++++if+(item1+==+null)
++++++++{
++++++++++++return+defaultValue;
++++++++}

++++++++return+getItem2(item1);
++++}
}|1935681|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 wrote a method that accepts a default value, here is how to use it:

<pre><code>var teacher = new Teacher();
return teacher.GetProperty(t =&gt; t.Name);
return teacher.GetProperty(t =&gt; t.Name, "Default name");
</code></pre>

Here is the code:

<pre><code>public static class Helper
{
 /// &lt;summary&gt;
 /// Gets a property if the object is not null.
 /// var teacher = new Teacher();
 /// return teacher.GetProperty(t =&gt; t.Name);
 /// return teacher.GetProperty(t =&gt; t.Name, "Default name");
 /// &lt;/summary&gt;
 public static TSecond GetProperty&lt;TFirst, TSecond&gt;(this TFirst item1,
 Func&lt;TFirst, TSecond&gt; getItem2, TSecond defaultValue = default(TSecond))
 {
 if (item1 == null)
 {
 return defaultValue;
 }

 return getItem2(item1);
 }
}
</code></pre>

blocks|key|1580303|text|在C#+6中，您可以使用空条件算子。所以最初的测试是：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1580304|int?+value+=+objectA?.PropertyA?.PropertyB?.PropertyC;|code-block|syntax|javascript|1580305|entityMap|0|LINK|mutability|MUTABLE|url|https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/member-access-operators#null-conditional-operators--and-^0|C|5|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]]]]

In C# 6 you can use the <a href="https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/member-access-operators#null-conditional-operators--and-" rel="noreferrer">Null Conditional Operator</a>. So the original test will be:

<pre><code>int? value = objectA?.PropertyA?.PropertyB?.PropertyC;
</code></pre>

blocks|key|383449|text|我在新的C#+6.0中看到了一些东西，这是通过使用'?‘而不是检查|type|unstyled|depth|inlineStyleRanges|entityRanges|data|383450|例如，而不是使用|383451|if+(Person+!=+null+&&+Person.Contact!=null+&&+Person.Contact.Address!=+null+&&+Person.Contact.Address.City+!=+null)
{+
++var+city+=+person.contact.address.city;
}|code-block|syntax|javascript|383452|你只需用|383453|var+city+=+person?.contact?.address?.city;|383454|我希望这能帮上忙。|383455|更新：|383456|你现在可以这样做|383457|+var+city+=+(Person+!=+null)?+
+++++++++++((Person.Contact!=null)?+
++++++++++++++((Person.Contact.Address!=+null)?
++++++++++++++++++++++((Person.Contact.Address.City!=null)?+
+++++++++++++++++++++++++++++++++Person.Contact.Address.City+:+null+)
+++++++++++++++++++++++:null)
+++++++++++++++:null)
++++++++++++:+null;|383458|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|11|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|12|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|13|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|14|8|@]|9|@]|A|$G|H]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

I saw something in the new C# 6.0,
this is by using '?' instead of checking 

for example instead of using 

<pre><code>if (Person != null &amp;&amp; Person.Contact!=null &amp;&amp; Person.Contact.Address!= null &amp;&amp; Person.Contact.Address.City != null)
{ 
 var city = person.contact.address.city;
}
</code></pre>

you simply use

<pre><code>var city = person?.contact?.address?.city;
</code></pre>

I hope it helped somebody. 

<hr>

UPDATE:

You could do like this now

<pre><code> var city = (Person != null)? 
 ((Person.Contact!=null)? 
 ((Person.Contact.Address!= null)?
 ((Person.Contact.Address.City!=null)? 
 Person.Contact.Address.City : null )
 :null)
 :null)
 : null;
</code></pre>

In C#, say that you want to pull a value off of PropertyC in this example and ObjectA, PropertyA and PropertyB can all be null.

ObjectA.PropertyA.PropertyB.PropertyC

How can I get PropertyC safely with the least amount of code?

Right now I would check:

<pre><code>if(ObjectA != null &amp;&amp; ObjectA.PropertyA !=null &amp;&amp; ObjectA.PropertyA.PropertyB != null)
{
 // safely pull off the value
 int value = objectA.PropertyA.PropertyB.PropertyC;
}
</code></pre>

It would be nice to do something more like this (pseudo-code).

<pre><code>int value = ObjectA.PropertyA.PropertyB ? ObjectA.PropertyA.PropertyB : defaultVal;
</code></pre>

Possibly even further collapsed with a null-coalescing operator.

EDIT Originally I said my second example was like js, but I changed it to psuedo-code since it was correctly pointed out that it would not work in js.

C# elegant way to check if a property's property is null

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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在C#中，假设您希望从本例中的PropertyC中提取一个值，而ObjectA、PropertyA和PropertyB都可以为null。ObjectA.PropertyA.PropertyB.PropertyC如何用最少的代码安全地获得PropertyC？现在我要查查：if(ObjectA != null && Obj...

问C#检查属性是否为空的优雅方法
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