ActionScript 3
Korzystanie z klasy proxy
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Wprowadzenie
Najpierw muszę powiedzieć. Jest powód dla którego ta sprawa Proxy, pomimo pozornej użyteczności, nie jest podświetlony na tyle w Internecie.
Nie można go użyć do oglądania losowej właściwości losowej klasy / instancji. Z tej techniki można korzystać tylko podklasując klasę Proxy .
Niektóre operacje nie oczekują wyjątków, więc musisz całkowicie zrozumieć, co robisz i dlaczego to robisz, a Twój kod musi być absolutnie czysty i bezbłędny.
Realizacja
Inną rzeczą dotyczącą klasy Proxy i tego, dlaczego nie jest ona tak popularna, jest to, że trudno jest pojąć problem, który dokładnie potrzebuje klasy dynamicznej z kontrolowanym dostępem do jej właściwości dynamicznych i metod jako najbardziej odpowiedniego rozwiązania. Za każdym razem, gdy próbowałem używać proxy, korzystałem z czegoś innego, prostszego i bardziej kontrolowanego.
Nie zniechęcajmy się jednak. Podoba mi się pomysł adresowania ostatnich elementów tablicy za pomocą indeksów [-1], [-2] itp. W Pythonie . To może nie być duży wyczyn, ale fajnie jest używać tego zamiast długiego i niezdarnego someArray [someArray.length - 1] . Zobaczmy, co możemy z tym zrobić.
package
{
import flash.utils.Proxy;
import flash.utils.flash_proxy;
/**
* Pyaray the Tentacled Whisperer of Impossible Secrets.
*/
dynamic public class PyArray extends Proxy
{
private var data:Array;
public function PyArray(...args:Array)
{
if (args.length == 0)
{
data = new Array;
}
else if ((args.length == 1) && (args[0] is Array))
{
data = args[0];
}
else
{
data = args;
}
}
// This is a getter proxy to all the available Array
// elements and properties and, sometimes, methods.
override flash_proxy function getProperty(name:*):*
{
var anIndex:int = name;
// Handle the int indices of the Array elements.
if (anIndex == name)
{
// Handle the -1, -2, etc indexing.
if (anIndex < 0) anIndex += data.length;
if (anIndex >= data.length) return null;
if (anIndex < 0) return null;
return data[anIndex];
}
// Handle the existing public Array properties.
if (data.hasOwnProperty(name)) return data[name];
// Handle the Array methods addressed via ["member"] access.
try
{
if (data[name] is Function) return data[name];
else throw new Error;
}
catch (fail:Error)
{
trace("[PyArray] is unable to resolve property \"" + name + "\".");
}
return null;
}
// This will set either elements, or settable properties.
override flash_proxy function setProperty(name:*, value:*):void
{
var anIndex:int = name;
// Handle the int indices of the Array elements.
if (anIndex == name)
{
// Handle the -1, -2, etc indexing.
if (anIndex < 0) anIndex += data.length;
// In case the element index is out of range,
// the PyArray will extend its data Array.
// if (anIndex >= data.length) return;
if (anIndex < 0) return;
data[anIndex] = value;
return;
}
// Handle the existing (or dynamic) public Array properties.
try
{
data[name] = value;
}
catch (fail:Error)
{
trace("[PyArray] is unable to set property \"" + name + "\".");
}
return;
}
// This allows to delete PyArray elements with "delete" operator.
override flash_proxy function deleteProperty(name:*):Boolean
{
var anIndex:int = name;
// Handle the int indices of the Array elements.
if (anIndex == name)
{
// Handle the -1, -2, etc indexing.
if (anIndex < 0) anIndex += data.length;
if (anIndex >= data.length) return false;
if (anIndex < 0) return false;
data.splice(anIndex, 1);
return true;
}
// Handle the dynamic public Array properties.
try
{
delete data[name];
return true;
}
catch (fail:Error)
{
trace("[PyArray] is unable to delete the \"" + name + "\" property.");
}
return false;
}
// This proxies any attempt to call a method on PyArray directly to data Array, thus
// all Array methods (including "toString" method called through trace) are available.
override flash_proxy function callProperty(name:*, ...rest):*
{
try
{
return (data[name] as Function).apply(data, rest);
}
catch (fail:Error)
{
trace("[PyArray] is unable to resolve method \"" + name + "\".");
return null;
}
}
// This allows PyArray to handle for..in and for..each..in loops.
// The initial call starts with zero, so we need to do this +1 -1 magic
// in order for enumeration to work correctly. I'm not happy with this either.
override flash_proxy function nextNameIndex(index:int):int
{
if (index >= data.length) return 0;
else return index + 1;
}
// This method handles the for..in loop.
override flash_proxy function nextName(index:int):String
{
return (index - 1).toString();
}
// This method handles the for..each..in loop.
override flash_proxy function nextValue(index:int):*
{
return data[index - 1];
}
}
}
Stosowanie
package
{
import flash.display.Sprite;
/**
* Daemonette of Slaanesh.
*
* It is minor female demon, vaguely human-like, but with crab-like pincers instead of hands.
* She wears a rather indecent skimpy leather bikini, moves quickly and casts deadly spells!
*/
public class Slaanesh extends Sprite
{
public function Slaanesh()
{
// Lets initialize the PyArray.
var PA:PyArray = new PyArray(1,2,3,4,5,4,3,2,1,"Foo");
// Basic check: get the last element.
trace(PA[-1]);
// output:
// Foo
// This will map to the 0-based third element.
trace(PA[2.0]);
// output:
// 3
// This should not get us anywhere.
trace(PA[2.1]);
// output:
// [PyArray] is unable to resolve property "2.1".
// null
// This should return the length of the data Array.
trace(PA["length"]);
// output:
// 10
// This should return the length of the data Array.
// This will not compile unless PyArray class is marked "dynamic".
trace(PA.length);
// output:
// 10
// This will map to indexOf method of data Array via getProperty method.
trace(PA["indexOf"]);
// output:
// function Function() {}
// This will map to indexOf method of data Array via getProperty method.
// This will not compile unless PyArray class is marked "dynamic".
trace(PA.indexOf);
// output:
// function Function() {}
// This is a try to access a non-existent property.
// This will not compile unless PyArray class is marked "dynamic".
trace(PA.P124);
// output:
// [PyArray] is unable to resolve property "P124".
// null
// This is a try to call a non-existent method via callProperty method.
// This will not compile unless PyArray class is marked "dynamic".
trace(PA.P124());
// output:
// [PyArray] is unable to resolve method "P124".
// null
// Basic check: calling a proxied method via callProperty method.
trace(PA.indexOf(5));
// output:
// 4
// An attempt to replace an Array method with a random value.
// This will not compile unless PyArray class is marked "dynamic".
PA.indexOf = 123;
// output:
// [PyArray] is unable to set property "indexOf".
// An attempt to assign a random value to a random property.
// It will succees because Array, as a dynamic class, allows so.
// This will not compile unless PyArray class is marked "dynamic".
PA.indexOfz = 123;
trace(PA.indexOfz);
// output:
// 123
// An attempt to assign an Array element via negative indexing.
// This trace works fine because toString method is also proxied.
PA[-3] = "Hello";
trace(PA);
// output:
// 1,2,3,4,5,4,3,Hello,1,Foo
// An attempt to delete Array elements via normal and negative indexing.
// This operation is mapped via deleteProperty method.
delete PA[-4]; // deletes "3" before "Hello"
delete PA[0]; // deletes "1" at the start.
trace(PA);
// output:
// 2,3,4,5,4,Hello,1,Foo
// An attempt to delete a non-dynamic method reference.
// There's no error output, AS3 must be handling this internally.
delete PA.indexOf;
trace(PA.indexOf);
// output:
// function Function() {}
// An attempt to set an element out of index range.
PA[10] = "123abc";
trace(PA);
// output:
// 2,3,4,5,4,Hello,1,Foo,,,123abc
var aText:String;
// This is a test of for..in loop, Array elements are
// enumerated via nextName and nextNameIndex methods.
aText = ""
for (var aKey:String in PA)
aText += aKey + ":" + PA[aKey] + " ";
trace(aText);
// output:
// 0:2 1:3 2:4 3:5 4:4 5:Hello 6:1 7:Foo 8:undefined 9:undefined 10:123abc
// This is a test of for..each..in loop, Array elements are
// enumerated via nextValue and nextNameIndex methods.
aText = "";
for each (var aValue:* in PA)
aText += aValue + " ";
trace(aText);
// output:
// 2 3 4 5 4 Hello 1 Foo undefined undefined 123abc
}
}
}