blocks|key|1529867|text|对数组使用'as‘。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1529868|var+badArray:Array;
badArray+=+Array(obj);|code-block|syntax|javascript|1529869|将产生一个长度为1的数组，原始数组在第一个元素中。如果你像下面这样使用'+as‘，你会得到预期的结果。|1529870|var+goodArray:Array;
goodArray+=+obj+as+Array;|1529871|通常，在ActionScript中，'+as‘比'Class()’更可取，因为它的行为更像是其他语言中的强制转换。|1529872|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Use 'as' with arrays.

<pre><code>var badArray:Array;
badArray = Array(obj);
</code></pre>

Will yield an array of length one with the original array in the first element. If you use 'as' as follows, you get the exptected result.

<pre><code>var goodArray:Array;
goodArray = obj as Array;
</code></pre>

Generally, 'as' is preferable to 'Class()' in ActionScript as it behaves more like casting in other languages.

blocks|key|1314783|text|您需要在两种情况下使用as进行转换:转换为Date和转换为Array。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1314784|对于日期，对Date(xxx)的调用与新Date().toString()的行为相同。|1314785|对于数组，调用Array(xxx)将创建一个Array，其中包含一个元素:+xxx。|1314786|已经证明Class()强制转换方法比as强制转换方法更快，因此当效率很重要时(以及当不使用日期和数组时)，它可能比as更可取。|1314787|import+flash.utils.*;

var+d+=+Date(+1+);

trace(+"'"+%2B+d,+"'is+type+of:+",getQualifiedClassName(+d+)+);

var+a:Array+=+Array(+d+);

trace(+"'"+%2B+a,+"'+is+type+of:+",+getQualifiedClassName(+a+)+);

++++//OUTPUT
++++++++//'Mon+Jun+15+12:12:14+GMT-0400+2009+'is+type+of:++String
++++++++//'Mon+Jun+15+12:12:14+GMT-0400+2009+'+is+type+of:++Array

++++//COMPILER+ERRORS/WARNINGS:
++++++++//Warning:+3575:+Date(x)+behaves+the+same+as+new+Date().toString().+
++++++++//To+cast+a+value+to+type+Date+use+"x+as+Date"+instead+of+Date(x).
++++++++//Warning:+1112:+Array(x)+behaves+the+same+as+new+Array(x).
++++++++//To+cast+a+value+to+type+Array+use+the+expression+x+as+Array+instead+of+Array(x).|code-block|syntax|javascript|1314788|`|1314789|entityMap^0|B|2|L|4|T|5|0|6|9|K|H|0|7|A|M|5|0|4|7|I|2|1L|2|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|11|8|@$9|12|A|13|B|C]|$9|14|A|15|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|16|8|@$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|1B|8|@$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]]|D|@]|E|$]]|$1|L|3|M|5|N|7|1I|8|@]|D|@]|E|$O|P]]|$1|Q|3|R|5|6|7|1J|8|@]|D|@]|E|$]]|$1|S|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]]|T|$]]

You need to use <code>as</code> to cast in two scenarios: casting to a <code>Date</code>, and casting to an <code>Array</code>.

For dates, a call to <code>Date(xxx)</code> behaves the same as new <code>Date().toString()</code>.

For arrays, a call to <code>Array(xxx)</code> will create an <code>Array</code> with one element: xxx.

The <code>Class()</code> casting method has been shown to be faster than <code>as</code> casting, so it may be preferable to <code>as</code> when efficiency matters (and when not working with Dates and Arrays).

<pre><code>import flash.utils.*;

var d = Date( 1 );

trace( "'" + d, "'is type of: ",getQualifiedClassName( d ) );

var a:Array = Array( d );

trace( "'" + a, "' is type of: ", getQualifiedClassName( a ) );

 //OUTPUT
 //'Mon Jun 15 12:12:14 GMT-0400 2009 'is type of: String
 //'Mon Jun 15 12:12:14 GMT-0400 2009 ' is type of: Array

 //COMPILER ERRORS/WARNINGS:
 //Warning: 3575: Date(x) behaves the same as new Date().toString(). 
 //To cast a value to type Date use "x as Date" instead of Date(x).
 //Warning: 1112: Array(x) behaves the same as new Array(x).
 //To cast a value to type Array use the expression x as Array instead of Array(x).
</code></pre>

`

blocks|key|1314881|text|在这个讨论中有几点值得注意。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1314882|两者的工作方式有很大的不同，Class()将尝试将对象强制转换为指定的Class，但如果做不到这一点，将(有时，取决于数据类型)抛出运行时错误。另一方面，使用object+as+Class将首先执行类型检查，如果指定的对象不能强制转换为指定的Class，则返回空值。|1314883|这是一个非常重要的区别，也是开发中的一个有用工具。它允许我们执行以下操作：|1314884|var+o:MyClass+=+myArray[i]+as+MyClass;

if(o)
{
++++//do+stuff
}|code-block|syntax|javascript|1314885|我认为这样做的用处是显而易见的。|1314886|"as“也与语言的其余部分更一致(例如："myObject+is+MyClass")。|1314887|MyClass()方法在处理简单数据类型(int、Number、uint、string)时还有其他优点。下面是一些示例：|1314888|var+s:String+=+"89567";
var+s2:String+=+"89+cat";
var+n:Number+=+1.9897;

var+i:int+=+int(s);+//+i+is+=+89567,+cast+works
var+i2:int+=+int(s2);+//Can't+convert+so+i2+is+set+to+0
var+i3:int+=+int(n);+//+i+=+1
var+n2:Number+=+Number(s2);+//+fails,+n2+=+NaN

//when+used+in+equations+you'll+get+very+different+results
var+result:int+=+int(n)+*+10;+//result+is+10
var+result:int+=+n+*+10;+//result+is+19.89700
var+result:int+=+int(s2)+*+10;+//result+is+0

trace(s2+as+Number);+//outputs+null
trace(s2+as+int);+//outputs+null
trace(Number(s2));+//outputs+NaN|1314889|这是一个很好也很重要的主题，作为一般规则，我在处理对象时使用"+as“，在使用更简单的数据类型时使用Cast()，但这正是我喜欢的代码结构。|1314890|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|Z|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|11|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|12|8|@]|9|@]|A|$]]|$1|Q|3|R|5|H|7|13|8|@]|9|@]|A|$I|J]]|$1|S|3|T|5|6|7|14|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

There are a couple of points in this discussion worth noting.

There is a major difference in how the two work, Class() will attempt to cast the object to the specified Class, but on failure to do so will (sometimes, depends on datatype) throw a runtime error. On the other hand using object as Class will preform a type check first, and if the specified object cannot be cast to the indicated Class a null value is returned instead.

This is a very important difference, and is a useful tool in development. It allows us to do the following:

<pre><code>var o:MyClass = myArray[i] as MyClass;

if(o)
{
 //do stuff
}
</code></pre>

I think the usefulness of that is pretty obvious. 

"as" is also more consistent with the rest of the language (ie: "myObject is MyClass").

The MyClass() method has additional benefits when working with simple data types (int, Number, uint, string) Some examples of this are:

<pre><code>var s:String = "89567";
var s2:String = "89 cat";
var n:Number = 1.9897;

var i:int = int(s); // i is = 89567, cast works
var i2:int = int(s2); //Can't convert so i2 is set to 0
var i3:int = int(n); // i = 1
var n2:Number = Number(s2); // fails, n2 = NaN

//when used in equations you'll get very different results
var result:int = int(n) * 10; //result is 10
var result:int = n * 10; //result is 19.89700
var result:int = int(s2) * 10; //result is 0

trace(s2 as Number); //outputs null
trace(s2 as int); //outputs null
trace(Number(s2)); //outputs NaN
</code></pre>

This is a good and important topic, as a general rule I use "as" when working with Objects and Cast() when using simpler data types, but that's just how I like to structure my code.

blocks|key|1530093|text|当我有一个对象的ArrayCollection，并且需要枚举它们，或者使用选择器函数时，我会使用它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1530094|例如：|1530095|var+abc:mytype+=+mycollection.getItemAt(i)+as+mytype|1530096|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

I use it when I have an ArrayCollection of objects and need to enumerate through them, or use a selector function.

e.g.

var abc:mytype = mycollection.getItemAt(i) as mytype

From what I understand of ActionScript, there are two kinds of casts:

<pre><code>var bar0:Bar = someObj as Bar; // "as" casting
var bar1:Bar = Bar(someObj); // "class name" casting (for want of a better name)
</code></pre>

Also, and please correct me if I'm wrong here, <code>as</code> casting will either return an instance of the class or <code>null</code>, while "class name" casting will either return an instance of the class or raise an exception if the cast is impossible – other than this, they are identical.

Given this, though, <code>as</code> casting seems to be a massive violation of the fail-fast-fail-early principle... And I'm having trouble imagining a situation where it would be preferable to use an <code>as</code> cast rather than a class name cast (with, possibly, an <code>instanceof</code> thrown in there).

So, my question is: under what circumstances would it be preferable to use <code>as</code> casting?

ActionScript: Is there ever a good reason to use 'as' casting?

据我对ActionScript的理解，有两种类型的类型转换：var bar0:Bar = someObj as Bar;  // "as" castingvar bar1:Bar = Bar(someObj); // "class name" casting (for want of a better name)另外，...

问ActionScript:有没有一个很好的理由来使用'as‘造型？
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