blocks|key|3329835|text|不是直截了当，但它说的就是真的。您的一个对象引用为空。当您尝试访问NULL对象的属性或方法时，您将看到这一点。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3329836|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|$]]

Not to be blunt but it means exactly what it says. One of your object references is NULL. You'll see this when you try and access the property or method of a NULL'd object.

blocks|key|3117212|text|这意味着你做了这样的事情。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3117213|Class+myObject+=+GetObjectFromFunction();|code-block|syntax|javascript|3117214|在没有的情况下使用|3117215|if(myObject!=null)，你去做myObject.Method();吧|offset|length|style|BOLD|CODE|3117216|entityMap^0|0|0|0|0|15|0|I|M|I|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|T|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|U|8|@$K|V|L|W|M|N]|$K|X|L|Y|M|O]|$K|Z|L|10|M|O]]|9|@]|A|$]]|$1|P|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|Q|$]]

It means you did something like this.

<pre><code>Class myObject = GetObjectFromFunction();
</code></pre>

And without doing 

<code>if(myObject!=null)</code>, you go ahead do <code>myObject.Method();</code>

blocks|key|347214|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|347215|这个错误是什么意思？对象引用未设置为对象的实例。|blockquote|347216|347217|347218|正如它所说的，您正在尝试使用空对象，就好像它是一个正确引用的对象一样。|347219|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|-4|4|5|6|J|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|K|7|@]|8|@]|9|$]]|$1|D|3|-4|4|5|6|L|7|@]|8|@]|9|$]]|$1|E|3|-4|4|5|6|M|7|@]|8|@]|9|$]]|$1|F|3|G|4|5|6|N|7|@]|8|@]|9|$]]|$1|H|3|-4|4|5|6|O|7|@]|8|@]|9|$]]]|I|$]]

<blockquote>
 what does this error mean? Object reference not set to an instance of an object.
</blockquote>

exactly what it says, you are trying to use a null object as if it was a properly
referenced object.

blocks|key|347223|text|大多数情况下，当您尝试将值传递到对象中时，如果值为null，则会发生此类异常。请查看this+link。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|347224|为了自学，你可以设置一些检查条件。喜欢|347225|if+(myObj==+null)
Console.Write("myObj+is+NULL");|code-block|syntax|javascript|347226|entityMap|0|LINK|mutability|MUTABLE|url|http://codebetter.com/blogs/raymond.lewallen/archive/2005/06/23/65033.aspx^0|16|9|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]]|C|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|X|8|@]|9|@]|C|$I|J]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]]]

Most of the time, when you try to assing value into object, and if the value is null, then this kind of exception occur.
Please check <a href="http://codebetter.com/blogs/raymond.lewallen/archive/2005/06/23/65033.aspx" rel="nofollow noreferrer">this link</a>.

for the sake of self learning, you can put some check condition. like

<pre><code>if (myObj== null)
Console.Write("myObj is NULL");
</code></pre>

blocks|key|347235|text|.NET中的变量可以是引用类型，也可以是值类型。值类型是诸如integers和booleans之类的原语或结构(可以识别，因为它们继承自System.ValueType。布尔型变量在声明时有一个默认值：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|347236|bool+mybool;
//mybool+==+false|code-block|syntax|javascript|347237|引用类型在声明时没有默认值：|347238|class+ExampleClass
{
}

ExampleClass+exampleClass;+//==+null|347239|如果您尝试使用空引用访问类实例的成员，则会得到一个System.NullReferenceException。这与未设置为对象实例的对象引用相同。|347240|下面的代码是一种简单的再现方法：|347241|static+void+Main(string[]+args)
{
++++var+exampleClass+=+new+ExampleClass();
++++var+returnedClass+=+exampleClass.ExampleMethod();
++++returnedClass.AnotherExampleMethod();+//NullReferenceException+here.
}

class+ExampleClass
{
++++public+ReturnedClass+ExampleMethod()
++++{
++++++++return+null;
++++}
}

class+ReturnedClass
{
++++public+void+AnotherExampleMethod()
++++{
++++}
}|347242|这是一个非常常见的错误，并且可能由于各种原因而发生。根本原因实际上取决于您遇到的特定场景。|347243|如果您使用的API或调用的方法可能返回null，那么正确地处理这一点很重要。可以修改上面的main方法，使NullReferenceException永远不会被用户看到：|347244|static+void+Main(string[]+args)
{
++++var+exampleClass+=+new+ExampleClass();
++++var+returnedClass+=+exampleClass.ExampleMethod();

++++if+(returnedClass+==+null)
++++{
++++++++//throw+a+meaningful+exception+or+give+some+useful+feedback+to+the+user!
++++++++return;
++++}

++++returnedClass.AnotherExampleMethod();
}|347245|以上所有内容实际上只是对.NET类型基础的提示，如果需要更多信息，我建议您选择CLR+via+C#或阅读同一位作者Jeffrey+Richter的这篇MSDN+article。此外，还可以查看更复杂的example，了解何时会遇到NullReferenceException。|347246|一些使用Resharper的团队利用JetBrains+attributes来注释代码，以突出显示哪里是(不)期望的空值。|347247|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/system.int32%2528loband%2529.aspx|1|http://msdn.microsoft.com/en-us/library/system.boolean(loband).aspx|2|http://msdn.microsoft.com/en-us/library/system.valuetype(loband%2529.aspx)|3|http://msdn.microsoft.com/en-us/library/system.nullreferenceexception%2528loband%2529.aspx|4|http://www.microsoft.com/learning/en/us/Books/6522.aspx|5|http://msdn.microsoft.com/en-us/magazine/cc301569.aspx|6|http://www.danielfortunov.com/software/$daniel_fortunovs_adventures_in_software_development/2009/04/23/net_event_invocation_thread_safety|7|https://www.jetbrains.com/resharper/help/Code_Analysis__Code_Annotations.html^0|U|8|0|13|8|1|1W|G|2|0|0|0|0|P|T|3|0|0|0|0|0|0|13|A|4|23|C|5|2S|7|6|0|I|K|7|0^^$0|@$1|2|3|4|5|6|7|1O|8|@]|9|@$A|1P|B|1Q|1|1R]|$A|1S|B|1T|1|1U]|$A|1V|B|1W|1|1X]]|C|$]]|$1|D|3|E|5|F|7|1Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|1Z|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|20|8|@]|9|@]|C|$G|H]]|$1|M|3|N|5|6|7|21|8|@]|9|@$A|22|B|23|1|24]]|C|$]]|$1|O|3|P|5|6|7|25|8|@]|9|@]|C|$]]|$1|Q|3|R|5|F|7|26|8|@]|9|@]|C|$G|H]]|$1|S|3|T|5|6|7|27|8|@]|9|@]|C|$]]|$1|U|3|V|5|6|7|28|8|@]|9|@]|C|$]]|$1|W|3|X|5|F|7|29|8|@]|9|@]|C|$G|H]]|$1|Y|3|Z|5|6|7|2A|8|@]|9|@$A|2B|B|2C|1|2D]|$A|2E|B|2F|1|2G]|$A|2H|B|2I|1|2J]]|C|$]]|$1|10|3|11|5|6|7|2K|8|@]|9|@$A|2L|B|2M|1|2N]]|C|$]]|$1|12|3|-4|5|6|7|2O|8|@]|9|@]|C|$]]]|13|$14|$5|15|16|17|C|$18|19]]|1A|$5|15|16|17|C|$18|1B]]|1C|$5|15|16|17|C|$18|1D]]|1E|$5|15|16|17|C|$18|1F]]|1G|$5|15|16|17|C|$18|1H]]|1I|$5|15|16|17|C|$18|1J]]|1K|$5|15|16|17|C|$18|1L]]|1M|$5|15|16|17|C|$18|1N]]]]

Variables in .NET are either reference types or value types. Value types are primitives such as <a href="http://msdn.microsoft.com/en-us/library/system.int32%28loband%29.aspx" rel="noreferrer">integers</a> and <a href="http://msdn.microsoft.com/en-us/library/system.boolean(loband).aspx" rel="noreferrer">booleans</a> or structures (and can be identified because they inherit from <a href="http://msdn.microsoft.com/en-us/library/system.valuetype(loband).aspx" rel="noreferrer">System.ValueType</a>). Boolean variables, when declared, have a default value:

<pre><code>bool mybool;
//mybool == false
</code></pre>

Reference types, when declared, do not have a default value:

<pre><code>class ExampleClass
{
}

ExampleClass exampleClass; //== null
</code></pre>

If you try to access a member of a class instance using a null reference then you get a <a href="http://msdn.microsoft.com/en-us/library/system.nullreferenceexception%28loband%29.aspx" rel="noreferrer">System.NullReferenceException</a>. Which is the same as Object reference not set to an instance of an object.

The following code is a simple way of reproducing this:

<pre><code>static void Main(string[] args)
{
 var exampleClass = new ExampleClass();
 var returnedClass = exampleClass.ExampleMethod();
 returnedClass.AnotherExampleMethod(); //NullReferenceException here.
}

class ExampleClass
{
 public ReturnedClass ExampleMethod()
 {
 return null;
 }
}

class ReturnedClass
{
 public void AnotherExampleMethod()
 {
 }
}
</code></pre>

This is a very common error and can occur because of all kinds of reasons. The root cause really depends on the specific scenario that you've encountered.

If you are using an API or invoking methods that may return null then it's important to handle this gracefully. The main method above can be modified in such a way that the NullReferenceException should never be seen by a user:

<pre><code>static void Main(string[] args)
{
 var exampleClass = new ExampleClass();
 var returnedClass = exampleClass.ExampleMethod();

 if (returnedClass == null)
 {
 //throw a meaningful exception or give some useful feedback to the user!
 return;
 }

 returnedClass.AnotherExampleMethod();
}
</code></pre>

All of the above really just hints of .NET Type Fundamentals, for further information I'd recommend either picking up <a href="http://www.microsoft.com/learning/en/us/Books/6522.aspx" rel="noreferrer">CLR via C#</a> or reading this <a href="http://msdn.microsoft.com/en-us/magazine/cc301569.aspx" rel="noreferrer">MSDN article</a> by the same author - Jeffrey Richter. Also check out, much more complex, <a href="http://www.danielfortunov.com/software/$daniel_fortunovs_adventures_in_software_development/2009/04/23/net_event_invocation_thread_safety" rel="noreferrer">example</a> of when you can encounter a NullReferenceException.

Some teams using Resharper make use of <a href="https://www.jetbrains.com/resharper/help/Code_Analysis__Code_Annotations.html" rel="noreferrer">JetBrains attributes</a> to annotate code to highlight where nulls are (not) expected.

blocks|key|342328|text|另一种简单的方法是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|342329|+Person+myPet+=+GetPersonFromDatabase();
+//+check+for+myPet+==+null...+AND+for+myPet.PetType+==+null
+if+(+myPet.PetType+==+"cat"+)+<---+fall+down+go+boom!|code-block|syntax|javascript|342330|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|$]]

Another easy way to get this:

<pre><code> Person myPet = GetPersonFromDatabase();
 // check for myPet == null... AND for myPet.PetType == null
 if ( myPet.PetType == "cat" ) &lt;--- fall down go boom!
</code></pre>

blocks|key|3330198|text|如果我有这个类：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3330199|public+class+MyClass
{
+++public+void+MyMethod()
+++{

+++}
}|code-block|syntax|javascript|3330200|然后我就做了：|3330201|MyClass+myClass+=+null;
myClass.MyMethod();|3330202|第二行抛出了这个异常，因为我在一个reference+type对象上调用了一个方法，这个对象是null+(也就是还没有通过调用myClass+=+new+MyClass()来instantiated+)|offset|length|style|CODE|3330203|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/490f96s2.aspx|1|http://msdn.microsoft.com/en-us/library/vstudio/dd460654.aspx^0|0|0|0|0|1B|4|1R|N|H|E|0|2F|C|1|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|14|8|@$M|15|N|16|O|P]|$M|17|N|18|O|P]]|9|@$M|19|N|1A|1|1B]|$M|1C|N|1D|1|1E]]|A|$]]|$1|Q|3|-4|5|6|7|1F|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]|Y|$5|T|U|V|A|$W|Z]]]]

If I have the class:

<pre><code>public class MyClass
{
 public void MyMethod()
 {

 }
}
</code></pre>

and I then do:

<pre><code>MyClass myClass = null;
myClass.MyMethod();
</code></pre>

The second line throws this exception becuase I'm calling a method on a <a href="http://msdn.microsoft.com/en-us/library/490f96s2.aspx" rel="nofollow">reference type</a> object that is <code>null</code> (I.e. has not been <a href="http://msdn.microsoft.com/en-us/library/vstudio/dd460654.aspx" rel="nofollow">instantiated</a> by calling <code>myClass = new MyClass()</code>)

blocks|key|3117365|text|简而言之，这意味着..。您正在尝试访问一个对象，但没有实例化它。您可能需要使用"new“关键字首先实例化它，即创建它的一个实例。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3117366|例如：|3117367|public+class+MyClass
{
+++public+int+Id+{get;+set;}
}

MyClass+myClass;

myClass.Id+=+0;+<-----------+An+error+will+be+thrown+here..+because+myClass+is+null+here...|code-block|syntax|javascript|3117368|您必须使用：|3117369|myClass+=+new+MyClass();
myClass.Id+=+0;|3117370|希望我说得很清楚..|3117371|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|T|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

In a nutshell it means.. You are trying to access an object without instantiating it.. You might need to use the "new" keyword to instantiate it first i.e create an instance of it.

For eg:

<pre><code>public class MyClass
{
 public int Id {get; set;}
}

MyClass myClass;

myClass.Id = 0; &lt;----------- An error will be thrown here.. because myClass is null here...
</code></pre>

You will have to use:

<pre><code>myClass = new MyClass();
myClass.Id = 0;
</code></pre>

Hope I made it clear..

I am receiving this error and I'm not sure what it means?

<blockquote>
 Object reference not set to an instance of an object.
</blockquote>

What does "Object reference not set to an instance of an object" mean?

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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我收到这个错误，但我不确定它是什么意思？未将对象引用设置为对象的实例。

问"Object reference not set to an object instance“是什么意思？
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问"Object reference not set to an object instance“是什么意思？
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