How can I tell if an Actionscript object has a certain dynamic property on it?

I have a dynamic Actionscript class as follows:

public dynamic class Foo {....}

In my code I (may) add some properties to it:

myFoo["myNewDynamicProp"] = "bar";

Elsewhere in my code, given an instance of class Foo, how can I determine if that dynamic prop开发者_运维问答erty has been added already without throwing an expensive exception?

You can do one of three things. First, calling a property that doesn't exist on a dyanmic instance doesn't throw an exception. It just returns undefined, so you can just test for that. Or you can use the in keyword. Or you can use the hasOwnProperty() method.

Consider the following:

var myFoo:Foo = new Foo();

myFoo.newProp = "bar";

trace(myFoo.newProp != undefined); // true
trace(myFoo.nothing != undefined); // false

trace("newProp" in myFoo); // true
trace("nothing" in myFoo); // false

trace(myFoo.hasOwnProperty("newProp")); // true
trace(myFoo.hasOwnProperty("nothing")); // false

You could also just as easily use bracket notation for the first example: myFoo['nothing']

Use the hasOwnProperty(property name) method for that :

if (myFoo.hasOwnProperty("myNewDynamicProp")) {
  // do whatever
}

You can also loop through the properties of any dynamic class using this:

for (var propertyName:String in myFoo)
{
  trace("Property " + propertyName + ": " + myFoo[propertyName]);
  if (propertyName == "myNewDynamicProp")
  {
      // found
      // may be do something
  }
}

This way you can not only check for your desired property, but also do more with the overall (dynamic) class properties.

You should just be able to do a simple null check like this:

if(myFoo.myNewDynamicProp) {
  //you can access it
}

Hope that helps