blocks|key|3160900|text|我更喜欢下面的语法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3160901|Dim+number+As+Integer+=+1
Dim+str+As+String+=+String.TryCast(number)

If+str+IsNot+Nothing+Then|code-block|syntax|javascript|3160902|哈，你可以看出我通常用C#写代码。8)|3160903|我更喜欢TryCast的原因是你不需要处理转换异常的开销。您的强制转换成功或您的变量被初始化为null，您将相应地进行处理。|3160904|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]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I prefer the following syntax:

<pre><code>Dim number As Integer = 1
Dim str As String = String.TryCast(number)

If str IsNot Nothing Then
</code></pre>

Hah you can tell I typically write code in C#. 8) 

The reason I prefer TryCast is you do not have to mess with the overhead of casting exceptions. Your cast either succeeds or your variable is initialized to null and you deal with that accordingly.

blocks|key|3160931|text|所有这些都略有不同，通常都有可接受的用法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3160932|3160933|var.ToString()将为您提供对象的字符串表示，而不管它是什么类型。如果var不是字符串already.|unordered-list-item|offset|length|style|CODE|3160934|CStr(var)是VB字符串转换运算符，则使用此选项。我不是一个使用VB的人，所以我建议避免使用它，但它不会真的伤害到任何东西。我认为这基本上与CType.|3160935|CType(var,+String)将给定类型转换为字符串基本相同，使用任何提供的转换operators.|3160936|DirectCast(var,+String)都可以将对象向上转换为字符串。如果你知道一个对象变量实际上是一个字符串，使用这个。这与C#.|3160937|TryCast中的(string)var+(如@NotMyself所述)类似于DirectCast，但如果变量不能转换为字符串，它将返回Nothing，而不是抛出异常。这与C#中的var+as+string相同。MSDN上的TryCast页面也有一个很好的比较。|3160938|3160939|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/system.object.tostring.aspx|1|http://msdn.microsoft.com/en-us/library/0zk841e9.aspx|2|http://msdn.microsoft.com/en-us/library/4x2877xb.aspx|3|http://msdn.microsoft.com/en-us/library/7k6y2h6x.aspx|4|http://msdn.microsoft.com/en-us/library/zyy863x8.aspx|5|https://stackoverflow.com/questions/40764/how-should-i-cast-in-vbnet#40771^0|0|0|0|E|14|3|4|8|0|0|0|9|21|5|0|4|1|0|0|I|0|5|2|0|0|N|0|A|3|0|0|7|9|B|13|A|1W|7|2I|D|34|7|0|7|4|O|9|5|0|0^^$0|@$1|2|3|4|5|6|7|1A|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|1C|8|@$F|1D|G|1E|H|I]|$F|1F|G|1G|H|I]]|9|@$F|1H|G|1I|1|1J]]|A|$]]|$1|J|3|K|5|E|7|1K|8|@$F|1L|G|1M|H|I]|$F|1N|G|1O|H|I]]|9|@$F|1P|G|1Q|1|1R]]|A|$]]|$1|L|3|M|5|E|7|1S|8|@$F|1T|G|1U|H|I]]|9|@$F|1V|G|1W|1|1X]]|A|$]]|$1|N|3|O|5|E|7|1Y|8|@$F|1Z|G|20|H|I]]|9|@$F|21|G|22|1|23]]|A|$]]|$1|P|3|Q|5|E|7|24|8|@$F|25|G|26|H|I]|$F|27|G|28|H|I]|$F|29|G|2A|H|I]|$F|2B|G|2C|H|I]|$F|2D|G|2E|H|I]|$F|2F|G|2G|H|I]]|9|@$F|2H|G|2I|1|2J]|$F|2K|G|2L|1|2M]]|A|$]]|$1|R|3|-4|5|6|7|2N|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|2O|8|@]|9|@]|A|$]]]|T|$U|$5|V|W|X|A|$Y|Z]]|10|$5|V|W|X|A|$Y|11]]|12|$5|V|W|X|A|$Y|13]]|14|$5|V|W|X|A|$Y|15]]|16|$5|V|W|X|A|$Y|17]]|18|$5|V|W|X|A|$Y|19]]]]

Those are all slightly different, and generally have an acceptable usage.

<ul>
<li><code>var.</code><a href="http://msdn.microsoft.com/en-us/library/system.object.tostring.aspx" rel="noreferrer"><code>ToString</code></a><code>()</code> is going to give you the string representation of an object, regardless of what type it is. Use this if <code>var</code> is not a string already.</li>
<li><a href="http://msdn.microsoft.com/en-us/library/0zk841e9.aspx" rel="noreferrer"><code>CStr</code></a><code>(var)</code> is the VB string cast operator. I'm not a VB guy, so I would suggest avoiding it, but it's not really going to hurt anything. I think it is basically the same as <code>CType</code>.</li>
<li><a href="http://msdn.microsoft.com/en-us/library/4x2877xb.aspx" rel="noreferrer"><code>CType</code></a><code>(var, String)</code> will convert the given type into a string, using any provided conversion operators.</li>
<li><a href="http://msdn.microsoft.com/en-us/library/7k6y2h6x.aspx" rel="noreferrer"><code>DirectCast</code></a><code>(var, String)</code> is used to up-cast an object into a string. If you know that an object variable is, in fact, a string, use this. This is the same as <code>(string)var</code> in C#.</li>
<li><a href="http://msdn.microsoft.com/en-us/library/zyy863x8.aspx" rel="noreferrer"><code>TryCast</code></a> (as mentioned by @<a href="https://stackoverflow.com/questions/40764/how-should-i-cast-in-vbnet#40771">NotMyself</a>) is like <code>DirectCast</code>, but it will return <code>Nothing</code> if the variable can't be converted into a string, rather than throwing an exception. This is the same as <code>var as string</code> in C#. The <code>TryCast</code> page on MSDN has a good comparison, too.</li>
</ul>

blocks|key|3160997|text|MSDN似乎表明，特定类型的Cxxx强制转换可以提高VB+.NET中的性能，因为它们被转换为内联代码。出于某些原因，它还建议在某些情况下使用DirectCast而不是CType+(文档中指出当存在继承关系时；我相信这意味着可以在编译时检查转换的健全性，并且可以应用优化，而CType始终使用VB运行时)。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3160998|当我编写VB+.NET代码时，我所使用的取决于我所做的事情。如果这是我要丢弃的原型代码，我会使用我输入的任何内容。如果这是我认真对待的代码，我会尝试使用Cxxx强制转换。如果一个不存在，如果我合理地相信存在继承关系，我就使用DirectCast。如果在这种情况下，我不知道转换是否应该成功(例如，用户输入->整数)，那么我使用TryCast是为了做一些比向用户抛出异常更友好的事情。|3160999|有一件事我不能动摇，那就是我倾向于使用ToString而不是CStr，但据说Cstr更快。|3161000|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/s2dy91zy%2528VS.80%2529.aspx|1|http://msdn.microsoft.com/en-us/library/7k6y2h6x.aspx^0|0|4|0|1Y|A|1|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@$A|S|B|T|1|U]|$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|Z|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|10|8|@]|9|@]|C|$]]]|I|$J|$5|K|L|M|C|$N|O]]|P|$5|K|L|M|C|$N|Q]]]]

<a href="http://msdn.microsoft.com/en-us/library/s2dy91zy%28VS.80%29.aspx" rel="noreferrer">MSDN</a> seems to indicate that the Cxxx casts for specific types can improve performance in VB .NET because they are converted to inline code. For some reason, it also suggests <a href="http://msdn.microsoft.com/en-us/library/7k6y2h6x.aspx" rel="noreferrer">DirectCast</a> as opposed to CType in certain cases (the documentations states it's when there's an inheritance relationship; I believe this means the sanity of the cast is checked at compile time and optimizations can be applied whereas CType always uses the VB runtime.)

When I'm writing VB .NET code, what I use depends on what I'm doing. If it's prototype code I'm going to throw away, I use whatever I happen to type. If it's code I'm serious about, I try to use a Cxxx cast. If one doesn't exist, I use DirectCast if I have a reasonable belief that there's an inheritance relationship. If it's a situation where I have no idea if the cast should succeed (user input -> integers, for example), then I use TryCast so as to do something more friendly than toss an exception at the user.

One thing I can't shake is I tend to use ToString instead of CStr but supposedly Cstr is faster.

blocks|key|3161021|text|我记得有一次，我看到MSDN库使用CStr()，因为它更快。不过，我不知道这是否属实。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3161022|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|$]]

At one time, I remember seeing the MSDN library state to use CStr() because it was faster. I do not know if this is true though.

blocks|key|366341|text|User+Konrad+Rudolph提倡for+DirectCast()+in+Stack+Overflow+question+"Hidden+Features+of+VB.NET"。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|366342|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/users/1968/konrad-rudolph|1|https://stackoverflow.com/questions/102084/hidden-features-of-vbnet#103285^0|5|E|0|L|1Z|1|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]|$A|R|B|S|1|T]]|C|$]]|$1|D|3|-4|5|6|7|U|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]|L|$5|G|H|I|C|$J|M]]]]

User <a href="https://stackoverflow.com/users/1968/konrad-rudolph">Konrad Rudolph</a> advocates <a href="https://stackoverflow.com/questions/102084/hidden-features-of-vbnet#103285">for DirectCast() in Stack Overflow question "Hidden Features of VB.NET"</a>.

blocks|key|3161056|text|Cstr()是内联编译的，以获得更好的性能。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3161057|如果定义了转换运算符，则CType允许在类型之间进行转换|3161058|如果不能进行转换，基类型和字符串之间的ToString()将抛出异常。|3161059|从字符串到基的TryParse()可能为typeif，否则返回false|3161060|如果类型通过继承相关或共享公共接口，则使用DirectCast。如果无法强制转换，则将引发异常。在此实例中，trycast将不返回任何内容|3161061|entityMap^0|0|6|0|C|5|0|J|A|0|7|A|K|6|0|L|A|1I|7|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|V|8|@$9|W|A|X|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|L|3|M|5|6|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|C]]|D|@]|E|$]]|$1|N|3|-4|5|6|7|18|8|@]|D|@]|E|$]]]|O|$]]

<code>Cstr()</code> is compiled inline for better performance.

<code>CType</code> allows for casts between types if a conversion operator is defined

<code>ToString()</code> Between base type and string throws an exception if conversion is not possible.

<code>TryParse()</code> From String to base <code>typeif</code> possible otherwise returns false

<code>DirectCast</code> used if the types are related via inheritance or share a common interface , will throw an exception if the cast is not possible, <code>trycast</code> will return nothing in this instance

blocks|key|3373934|text|根据认证考试，对于简单的转换，您应该尽可能使用Convert.ToXXX()，因为它比CXXX转换更优化性能。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3373935|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|$]]

According to the certification exam you should use Convert.ToXXX() whenever possible for simple conversions because it optimizes performance better than CXXX conversions.

Are all of these equal? Under what circumstances should I choose each over the others?

<ul>
<li>var.ToString()</li>
<li>CStr(var)</li>
<li>CType(var, String)</li>
<li>DirectCast(var, String)</li>
</ul>

<hr>

EDIT: Suggestion from <a href="https://stackoverflow.com/users/303/notmyself">NotMyself</a>&hellip;

<ul>
<li>TryCast(var, String)</li>
</ul>

How should I cast in VB.NET?

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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所有这些都相等吗？在什么情况下，我应该选择其中的一个？var.ToString()CStr(var)CType(var，String)DirectCast(var，字符串)编辑:来自…的建议TryCast(var，字符串)

问我应该如何在VB.NET中进行强制转换？
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问我应该如何在VB.NET中进行强制转换？
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