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Transferring data with AIR native extensions for iOS – Part 3: Exchanging custom objects between ActionScript 3 and C, C++, or Objective-C

by Tom Krcha

Content

Exchanging custom objects between ActionScript 3 and C
Where to go from here

Created

16 July 2012

Requirements

Prerequisite knowledge

To make the most of this article, you’ll need a good understanding of ActionScript, C, Flash Builder, Xcode, and using tools from the command line.

Additional required other products

Xcode

Learn more

User level

Intermediate

In Part 1 of this series I showed how to exchange basic types such as Number, int, uint, String, and Boolean data between ActionScript 3 and C (or C++, C#, or Objective-C) for native extensions on iOS. In Part 2, I showed how to use the same approach with arrays and Vector objects. In this article, I extend the technique to custom objects.

If you haven’t done so already, I recommend reading Part 1 and Part 2 before proceeding with this article.

Exchanging custom objects between ActionScript 3 and C

There are situations in which you want to transfer a custom object instead of a predefined object or a basic type. For example, you may want to exchange an array of positions in three dimensions. Position is, in this case, defined by an object with x, y, and z properties.

The first step is to initiate an Array instance. You can use the same approach outlined in Part 2: Exchanging Vector and Array objects between ActionScript 3 and C, C++, or Objective-C:

        uint32_t arr_len = 10; // count of positions
FREObject objectsPosition = NULL;
FRENewObject((const uint8_t*)"Array", 0, NULL, &objectsPosition, NULL);
FRESetArrayLength(objectsPosition, arr_len);

    

Next, define a custom Object, as you did with the Array in Part 2. Here is an example from the getArrayOfPositions() function in the sample code:

        // loop through array length and fill it with data
for(uint32_t i=0;i<arr_len;i++){
 
FREObject position;
// create an instance of Object and save it to FREObject position
FRENewObject((const uint8*)"Object", 0, NULL, &position,NULL);
 
// populate temporary vars x, y, z
FREObject xPos;
FREObject yPos;
FREObject zPos;
FRENewObjectFromInt32(10, &xPos);
FRENewObjectFromInt32(20, &yPos);
FRENewObjectFromDouble(30, &zPos);
 
// fill properties of FREObject position
FRESetObjectProperty(position, (const uint8*)"x", zPos, NULL);
FRESetObjectProperty(position, (const uint8*)"y", yPos, NULL);
FRESetObjectProperty(position, (const uint8*)"z", zPos, NULL);
 
// add position to the array
FRESetArrayElementAt(objectsPosition, i, position);
}

    

The sample code for this article contains the following ActionScript functions:

              public function getArrayOfPositions():Array{
         return context.call("getArrayOfPositions");
      }

    

Here is the associated C code:

        FREObject getArrayOfPositions(FREContext ctx, void* funcData, uint32_t argc, FREObject argv[]){

    uint32_t arr_len = 10; // count of positions
    FREObject objectsPosition = NULL;
    FRENewObject((const uint8_t*)"Array", 0, NULL, &objectsPosition, NULL);
    FRESetArrayLength(objectsPosition, arr_len);

    // loop through array length and fill it with data
    for(uint32_t i=0;i<arr_len;i++){
    
        FREObject position;
        // create an instance of Object and save it to FREObject position
        FRENewObject((const uint8_t*)"Object", 0, NULL, &position,NULL);
    
        // populate temporary vars x, y, z
        FREObject xPos;
        FREObject yPos;
        FREObject zPos;
        FRENewObjectFromInt32(10, &xPos);
        FRENewObjectFromInt32(20, &yPos);
        FRENewObjectFromDouble(30, &zPos);
    
        // fill properties of FREObject position
        FRESetObjectProperty(position, (const uint8_t*)"x", zPos, NULL);
        FRESetObjectProperty(position, (const uint8_t*)"y", yPos, NULL);
        FRESetObjectProperty(position, (const uint8_t*)"z", zPos, NULL);
    
        // add position to the array
        FRESetArrayElementAt(objectsPosition, i, position);
    }
    
    
    return objectsPosition;
}

    

The code above shows how to transfer instances of Object type. You can also define your own type; for instance a Position type that includes x, y, and rotation properties.

The sample code also includes support for getting an individual instance of this Position type. The class is defined in Position.as:

        package com.krcha
{
   [RemoteClass(alias="com.krcha.Position")]
   public class Position
   {
      
      public var x:uint;
      public var y:uint;
      public var rotation:Number;
      
   }
}

    

The ActionScript function is in IOSExtension.as:

        public function getPosition():Position{
   return context.call("getPosition") as Position;
}

    

Here is the related C function from IOSExtension.m:

        FREObject getPosition(FREContext ctx, void* funcData, uint32_t argc, FREObject argv[]){
    
    uint32_t arr_len = 10; // count of positions
    FREObject position = NULL;
    FRENewObject((const uint8_t*)"com.krcha.Position", 0, NULL, &position, NULL);
    FRESetArrayLength(position, arr_len);
    
    FREObject xPos;
    FREObject yPos;
    FREObject rotation;
    
    FRENewObjectFromInt32(10, &xPos);
    FRENewObjectFromInt32(20, &yPos);
    FRENewObjectFromDouble(1.57f, &rotation);
    
    FRESetObjectProperty(position, (const uint8_t*)"x", xPos, NULL);
    FRESetObjectProperty(position, (const uint8_t*)"y", yPos, NULL);
    FRESetObjectProperty(position, (const uint8_t*)"rotation", rotation, NULL);
    
    return position;
}

    

Where to go from here

To learn more about native extensions check out the Native C API Reference for Adobe AIR extensions.

Also be sure to visit Native extensions for Adobe AIR in the Adobe AIR developer center.

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