blocks|key|1414824|text|这是一种方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1414825|if+(!(sender+is+TextBox))+{...}|code-block|syntax|javascript|1414826|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 is one way:

<pre><code>if (!(sender is TextBox)) {...}
</code></pre>

blocks|key|1414838|text|你不能用更冗长的“老”方法，在is关键字之前：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1414839|if+(sender.GetType()+!=+typeof(TextBox))+{+//+...+}|code-block|syntax|javascript|1414840|entityMap^0|F|2|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Couldn't you also do the more verbose "old" way, before the <code>is</code> keyword:

<pre><code>if (sender.GetType() != typeof(TextBox)) { // ... }
</code></pre>

blocks|key|1414845|text|尝尝这个。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1414846|var+cont=+textboxobject+as+Control;
if(cont.GetType().Name=="TextBox")
{
+++MessageBox.show("textboxobject+is+a+textbox");
}+|code-block|syntax|javascript|1414847|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.

<pre><code>var cont= textboxobject as Control;
if(cont.GetType().Name=="TextBox")
{
 MessageBox.show("textboxobject is a textbox");
} 
</code></pre>

blocks|key|1414879|text|如果使用继承，如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1414880|public+class+BaseClass
{}
public+class+Foo+:+BaseClass
{}
public+class+Bar+:+BaseClass
{}|code-block|syntax|javascript|1414881|..。抗零值|1414882|if+(obj?.GetType().BaseType+!=+typeof(Bar))+{+//+...+}|1414883|或|1414884|if+(!(sender+is+Foo))+{+//...+}|1414885|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

If you use inheritance like:

<pre><code>public class BaseClass
{}
public class Foo : BaseClass
{}
public class Bar : BaseClass
{}
</code></pre>

...
Null resistant

<pre><code>if (obj?.GetType().BaseType != typeof(Bar)) { // ... }
</code></pre>

or

<pre><code>if (!(sender is Foo)) { //... }
</code></pre>

blocks|key|1414986|text|两种常见的方法是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1414987|1)使用IS运算符：|1414988|if+(!(sender+is+TextBox))+{...}|code-block|syntax|javascript|1414989|2)使用AS运算符(如果您还需要使用textBox实例，则非常有用)：|1414990|var+textBox+=+sender+as+TextBox;++
if+(sender+==+null)+{...}|1414991|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Two well-known ways of doing it are :

1) Using IS operator:

<pre><code>if (!(sender is TextBox)) {...}
</code></pre>

2) Using AS operator (useful if you also need to work with the textBox instance) :

<pre><code>var textBox = sender as TextBox; 
if (sender == null) {...}
</code></pre>

blocks|key|1415029|text|C#+9允许使用not运算符。你可以直接使用|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1415030|if+(sender+is+not+TextBox)+{...}|code-block|syntax|javascript|1415031|而不是|1415032|if+(!(sender+is+TextBox))+{...}|1415033|entityMap|0|LINK|mutability|MUTABLE|url|https://devblogs.microsoft.com/dotnet/welcome-to-c-9-0/#logical-patterns^0|8|3|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

C# 9 allows using the <a href="https://devblogs.microsoft.com/dotnet/welcome-to-c-9-0/#logical-patterns" rel="noreferrer">not</a> operator. You can just use
<pre><code>if (sender is not TextBox) {...}
</code></pre>
instead of
<pre><code>if (!(sender is TextBox)) {...}
</code></pre>

This works just fine:

<pre><code> protected void txtTest_Load(object sender, EventArgs e)
 {
 if (sender is TextBox) {...}

 }
</code></pre>

Is there a way to check if sender is NOT a TextBox, some kind of an equivalent of != for "is"?

Please, don't suggest moving the logic to ELSE{} :)

Check if object is NOT of type (!= equivalent for "IS") - C#

这个很好用：    protected void txtTest_Load(object sender, EventArgs e)    {        if (sender is TextBox) {...}    }有没有办法检查发送者是否不是TextBox，某种等同于!=表示" Is“的东西？请不要建议将逻辑移...

问检查对象是否不是类型(!=等同于" is ") - C#
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