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Using the same function with different extended object types

Posted on 2011-03-07
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Last Modified: 2012-05-11
Hi still being very green with Actionscript, I wonder if you could help with the following,

For the sake of an example think of a page in a book where,

I have 4 seperate classes,  ParagraphData, PartHeadingData, FooterData and ListData each which extend from the PageItemData class, a pageItem being its namesake on a page and each class has a different set of extended properties

Each "page of the book" as such is presented in an array called pageData and contains for example 3 instances of ParagraphData, 1 PartHeadingData , 1 list etc
 
What I need to do is iterate over the pageData array and act accordingly depending on what object type is currently being examined.

I have tried the following but with no success.

for each (var pageItem:PageItemData in pageData){
                        
      //check for prefix span and add if true            
                        if (pageItem.has_Prefix_Span && pageItem.prefix_Span_Text!==""){
                              createParagraphPrefixSpan(pageItem,pElem)
                        }
                              
      //check for inline graphic      
                        if ((pageItem.paragraph_Contains_Figure)as ParagraphData){
                        pElem=figure.checkForFigure(pageItem,pElem,figureData);
                        }

The first portion works because of the properties within the PageItemData class which are common to all , but the second does not ,even if I try to cast to the correct datatype, the compiler keeps complaining about


1118: Implicit coercion of a value with static type vo:PageItemData to a possibly unrelated type vo:ParagraphData

1119: Access of possibly undefined property paragraph_Contains_Figure through a reference with static type vo:PageItemData

I know I could replace the first line with

for each (var pageItem:* in pageData){

but this seems odd to me seing as all the items being iterated over are extended from the type shown.

What am I missing here and thanks in advance

John


}
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Question by:BloodGrinder
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Accepted Solution

by:
ChristoferDutz earned 500 total points
ID: 35056986
Well I'd to some checks the following way:
if(pageItem is ParagraphData) {
   var paragraphData:ParagraphData = ParagraphData(pageItem);

   ... work with paragraphData ...

} 

Open in new window


In the if-part you check if the type is the one you expect.
If it is I tend to define a local varialbe containing a casted reference to the type I did my check for. This makes working with it a lot easier.

By the way ... I wouldn't write "!==" ... I think you are looking for "!=" (Actually I don't know what !== actually does think it's a check for instance equality)
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Author Closing Comment

by:BloodGrinder
ID: 35113072
Apologies I thought i had closed this 3 days ago
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