blocks|key|707758|text|这些是指令或“预处理器指令”。它们基本上允许对VB代码进行条件编译。以下是与VB相关的MSDN文章：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|707759|http://msdn.microsoft.com/en-us/library/tx6yas69.aspx|offset|length|707760|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|1H|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@$D|O|E|P|1|Q]]|A|$]]|$1|F|3|-4|5|6|7|R|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|C]]]]

Those are directives or "pre-processor directives". They basically allow for conditional compiling of VB code. Here is the VB-related MSDN article:

<a href="http://msdn.microsoft.com/en-us/library/tx6yas69.aspx" rel="nofollow noreferrer">http://msdn.microsoft.com/en-us/library/tx6yas69.aspx</a>

blocks|key|3023419|text|它是一个Preprocessor+Directive|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3023420|E预处理指令提供了有条件地跳过源文件的部分、报告错误和警告条件以及描述源代码的不同区域的功能|3023421|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/ed8yd1ha(VS.71).aspx^0|4|M|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

It is a <a href="http://msdn.microsoft.com/en-us/library/ed8yd1ha(VS.71).aspx" rel="nofollow noreferrer">Preprocessor Directive</a>

e pre-processing directives provide the ability to conditionally skip sections of source files, to report error and warning conditions, and to delineate distinct regions of source code

blocks|key|3023444|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3023445|从表面上看，#If...Then...#Else指令的行为与If...Then...Else语句的行为相同。但是，#If...Then...#Else指令评估编译器编译的内容，而If...Then...Else语句在运行时评估条件。|blockquote|offset|length|style|CODE|3023446|3023447|3023448|http://msdn.microsoft.com/en-us/library/tx6yas69.aspx|3023449|entityMap|0|LINK|mutability|MUTABLE|url^0|0|6|I|0|0|0|0|1H|0|0^^$0|@$1|2|3|-4|4|5|6|S|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|T|7|@$D|U|E|V|F|G]]|8|@]|9|$]]|$1|H|3|-4|4|5|6|W|7|@]|8|@]|9|$]]|$1|I|3|-4|4|5|6|X|7|@]|8|@]|9|$]]|$1|J|3|K|4|5|6|Y|7|@]|8|@$D|Z|E|10|1|11]]|9|$]]|$1|L|3|-4|4|5|6|12|7|@]|8|@]|9|$]]]|M|$N|$4|O|P|Q|9|$R|K]]]]

<blockquote>
 On the surface, the behavior of the
 <code>#If...Then...#Else</code> directives appears the same as that of the
 If...Then...Else statements. However,
 the #If...Then...#Else directives
 evaluate what is compiled by the
 compiler, whereas the If...Then...Else
 statements evaluate conditions at run
 time.
</blockquote>

<a href="http://msdn.microsoft.com/en-us/library/tx6yas69.aspx" rel="nofollow noreferrer">http://msdn.microsoft.com/en-us/library/tx6yas69.aspx</a>

blocks|key|707900|text|#If...Then...#Else是一个预处理器指令，它允许根据特定条件编译代码的某些部分。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|707901|它的功能与常规If...Then...Else语句类似，但不同之处在于，条件是在编译程序时计算条件。这会导致代码的某些部分无法编译。|707902|当您希望为应用程序的调试版本而不是发行版编译某些代码时，#If可能会很有用。以下面的代码为例。通过编写以下代码，将在调试模式下编译Beep()节，但当项目的输出类型更改为Release时，将不会编译该节。|707903|#If+DEBUG+Then
++++++++'beep+once+in+debug+mode
++++++++Beep()
#Else
++++++++'do+nothing
#End+If|code-block|syntax|javascript|707904|#If指令适用于Conditional+Compilation+Directives。这些是在编译时计算的“变量”，用来确定要编译代码的哪些部分。|707905|在标准项目中，您可以使用以下条件编译指令：|707906|707907|CONFIG:+(字符串)调试或Release|unordered-list-item|BOLD|707908|DEBUG:+(int32，可计算为布尔值)+-1+(或True)如果项目配置为32位或64位编译模式的|707909|CONFIG：(字符串)+winexe+(字符串)winexe(用于Windows窗体应用程序和Windows服务)，exe+(用于控制台应用程序)和库(用于类库和Web控件Library|707910|TRACE:+(int32，可以计算为布尔值)+-1+(或真)如果跟踪常量为defined.|707911|VBC_VER:+(双精度？*不确定)表示VB.NET编译器的版本号。|707912|707913|707914|使用这些条件编译指令，您可以轻松地将代码的某些部分编译到输出中或不编译到输出中。|707915|进一步阅读：|707916|707917|Conditional+Compilation+in+Visual+Basic|707918|#If...Then...#Else+Directives|707919|#Const+Directive|707920|707921|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/deszhz3d.aspx|1|http://msdn.microsoft.com/en-us/library/x435tkbk.aspx|2|http://msdn.microsoft.com/en-us/library/tx6yas69.aspx|3^0|0|I|0|7|G|0|S|3|1T|6|0|0|0|3|8|Y|0|0|0|0|0|7|0|0|6|1|0|7|1|0|6|1|0|8|1|0|0|0|0|0|0|13|1|0|0|T|2|0|0|G|3|0|0^^$0|@$1|2|3|4|5|6|7|1W|8|@$9|1X|A|1Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1Z|8|@$9|20|A|21|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|22|8|@$9|23|A|24|B|C]|$9|25|A|26|B|C]]|D|@]|E|$]]|$1|J|3|K|5|L|7|27|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|28|8|@$9|29|A|2A|B|C]]|D|@$9|2B|A|2C|1|2D]]|E|$]]|$1|Q|3|R|5|6|7|2E|8|@]|D|@]|E|$]]|$1|S|3|-4|5|6|7|2F|8|@]|D|@]|E|$]]|$1|T|3|U|5|V|7|2G|8|@$9|2H|A|2I|B|W]]|D|@]|E|$]]|$1|X|3|Y|5|V|7|2J|8|@$9|2K|A|2L|B|W]]|D|@]|E|$]]|$1|Z|3|10|5|V|7|2M|8|@$9|2N|A|2O|B|W]]|D|@]|E|$]]|$1|11|3|12|5|V|7|2P|8|@$9|2Q|A|2R|B|W]]|D|@]|E|$]]|$1|13|3|14|5|V|7|2S|8|@$9|2T|A|2U|B|W]]|D|@]|E|$]]|$1|15|3|-4|5|6|7|2V|8|@]|D|@]|E|$]]|$1|16|3|-4|5|6|7|2W|8|@]|D|@]|E|$]]|$1|17|3|18|5|6|7|2X|8|@]|D|@]|E|$]]|$1|19|3|1A|5|6|7|2Y|8|@]|D|@]|E|$]]|$1|1B|3|-4|5|6|7|2Z|8|@]|D|@]|E|$]]|$1|1C|3|1D|5|V|7|30|8|@]|D|@$9|31|A|32|1|33]]|E|$]]|$1|1E|3|1F|5|V|7|34|8|@]|D|@$9|35|A|36|1|37]]|E|$]]|$1|1G|3|1H|5|V|7|38|8|@]|D|@$9|39|A|3A|1|3B]]|E|$]]|$1|1I|3|-4|5|6|7|3C|8|@]|D|@]|E|$]]|$1|1J|3|-4|5|6|7|3D|8|@]|D|@]|E|$]]]|1K|$1L|$5|1M|1N|1O|E|$1P|1Q]]|1R|$5|1M|1N|1O|E|$1P|1S]]|1T|$5|1M|1N|1O|E|$1P|1U]]|1V|$5|1M|1N|1O|E|$1P|1Q]]]]

The <code>#If...Then...#Else</code> is a preprocessor directive that allows certain parts of your code to be compiled based on certain conditions.
It functions just like a regular <code>If...Then...Else</code> statement but the difference is that the condition is evaluated when the program is being compiled. this results in some portions of the code not being compiled.
The <code>#If</code> can be useful when you want some code to be compiled for Debug versions of your application but not for the release. Take for example the code below. By writing the code below, the <code>Beep()</code> section will be compiled in Debug mode but when the project's output type is changed to Release, that section will not be compiled.
<pre><code>#If DEBUG Then
 'beep once in debug mode
 Beep()
#Else
 'do nothing
#End If
</code></pre>
The <code>#If</code> directive works with <a href="http://msdn.microsoft.com/en-us/library/deszhz3d.aspx" rel="nofollow noreferrer">Conditional Compilation Directives</a>. These are the 'variables' that are evaluated at compile time to determine which parts of your code to compile.
In a standard project you have the following conditional compilation directives:
<ul>
<li>CONFIG: (String) Either Debug or Release</li>
<li>DEBUG: (int32, can evaluate as boolean) -1 (or True) if project configuration is debug.</li>
<li>PLATFORM: (String) x86 or x64 for 32-bit or 64-bit compilation mode respectively.</li>
<li>TARGET: (string) winexe for Windows Forms Application and Windows Service, exe for Console Applications and library for Class Library and Web Control Library</li>
<li>TRACE: (int32, can evaluate as boolean) -1 (or True) if Trace constant is defined.</li>
<li>VBC_VER: (double? *not sure) Indicates the version number of the VB.NET compiler.</li>
</ul>
Using these conditional compilation directives, you can easily have certain parts of your code compile into the output or not.
 
<h3>Further Reading:</h3>
<ul>
<li><a href="http://msdn.microsoft.com/en-us/library/x435tkbk.aspx" rel="nofollow noreferrer">Conditional Compilation in Visual Basic</a></li>
<li><a href="http://msdn.microsoft.com/en-us/library/tx6yas69.aspx" rel="nofollow noreferrer">#If...Then...#Else Directives</a></li>
<li><a href="http://msdn.microsoft.com/en-us/library/deszhz3d.aspx" rel="nofollow noreferrer">#Const Directive</a></li>
</ul>

blocks|key|707822|text|可以使用#If/#Else/#EndIf指令告诉编译器、Intellisense等忽略代码段。如果将某些代码包含在"If+False+Then+...+End+If“语句中，代码将永远不会执行，但编译器仍会处理它，并且Intellisense仍会更新它。如果程序的一部分被"#If+False+...+#EndIf“包围，它本质上将被视为注释。没有要求"#If+False“指令中的内容在语法上是有效的，像"Rename+variable”这样的工具也不会影响它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|707823|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|$]]

The #If/#Else/#EndIf directives may be used to tell the compiler, Intellisense, etc. to ignore sections of code. If one encloses some code in an "If False Then ... End If" statement, the code will never execute, but the compiler will still process it, and Intellisense will still update it. If part of a program is surrounded by "#If False ... #EndIf", it will be essentially regarded as comments. There is no requirement that the stuff within a "#If False" directive be syntactically valid, and tools like "Rename variable" will not affect it.

blocks|key|3023544|text|举个例子(其他人已经回答了#-directive是什么)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3023545|#IF+debug=true
+userhandler.login("stefan","mypassword")
#else
+userhandler.login(usernameTextbox.text,userpasswordTextbox.text)
#end+if|code-block|syntax|javascript|3023546|当您在调试模式下运行代码时，编译器将自动处理IF条件的true部分中的代码。当您将项目设置为发布并重新生成项目时，它将使用if条件的其他部分。通过这种方式，您可以使作为程序员的生活更容易用于测试目的和许多其他场景。|3023547|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|$]]

Just to give an examlpe (other has allready answered WHAT #-directive is):

<pre><code>#IF debug=true
 userhandler.login("stefan","mypassword")
#else
 userhandler.login(usernameTextbox.text,userpasswordTextbox.text)
#end if
</code></pre>

When you run your code in debug mode the compiler will automatically handle the code in the true-part of the IF-condition. When you set the project to release and rebuild the project, it will use the other part of the if-condition. That way you can make the live as a programmer more easy for testing purposes and much other scenarios.

Google is not good for searching for the # symbol

What effect does the # in front of the if make?

I am cleaning up someones mess and have never seen this before

VB #If KeyWord - Effect Of #

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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谷歌不擅长搜索#符号if前面的#会产生什么效果？我正在清理别人的烂摊子，以前从未见过这样的事情

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