How To: Assigning a value to a sub property of an indexed default property via "setter"

I have a class which contains the profile information of a project of mine, with loads and loads of information, its called PROFILE. To have an easy access to all the different properties of this profile I have an indexed default property. This default property(TCHANNELLIST) is a record containig again a few properties as well as another record(TCHANNELPARAMETER). The property CHANNEL is the default property (indexed) of the default property TCHANNELLIST.

Now I do have a problem when constructing the setter of these properties. (To clearify: the read function is not the problem! Please don't bother except the solution can be found in it).

The Question: How do I construct the Property/procedure/function to get the following code running

MyProfile[i][j].Name := 'Thanks_for_the_help';

Since more is more here is the structure of my records I have used. I am also willing to change the general structure if there is a better way, so I am open for suggestions.

TChannelParameter = record                                                        
  // each channel gets one record for itself
  public
    channelType                     : TKanalTyp;
    display_number                  : Integer;    
    Name                            : string;
    // and a few other but you will get the idea...
  end;

TChannelList = record
  private
    FChannelparameter_List           : array of TChannelParameter ; 
    function GetChannelParameter(Index: Integer): TChannelParameter ;
    procedure SetChannelParameter(Index: Integer); //Here I need some help
  public
    property Channal_GlobalNumber[index: Integer]: TChannelParameter read GetChannelParameter write SetChannelParameter; //Here I need some help
  end;

To be honest I just don't have an idea (and I cant find any help online) to get that line of code running. To Read everything is not a problem but to write stuff into the "subitem" of an indexed default property is a riddle to me. Here it does not matter if I use this

A_Channel_list[i].name := 'aName';

MyProfile[i][j].name := 'aName';

Both setters are till now not constructed! Since I lack the basic knowledge to do so! (further I did not include the class since the handling should be the same)

If I get one running the other one should not be a problem anymore. Maybe somebody knows that this kind of operation however is not possible, please also let me know this! I will then reconstruct my class and records.

Solution

For what you are trying to achieve you don't even need Channal_GlobalNumber property to be writable. Having it readable would be enough provided that your TChannelParameter object is class type instead record type that you have now.

You see if you declare your TChannelParameter as class your Channal_GlobalNumber property will return you a reference (pointer) to that object so you can then access any of its fields/properties like if you would have variable referencing such object.

This means that you could then be changing name property/field of individual channels simply by using:

A_Channel_list[i].name := 'aName';

So why doesn't this work when your TChannelParameter is of record type. As Uwe Raabe wrote in his comment your indexed property of record type won't return you the original record from your array but instead a copy of it. Therefore making any hanges on it would not change the original record from your array but instead copy.

EDIT: Don't forget that if you change your TChannelParameter object to class type you will have to write special routines for creating such object when you are changing size of your FChannelparameter_List array as in such case this array is array of poiters to TChannelParameter classes.

Now if you want to realy avoid this and use records only you could write multiple indexed properties in TChannelList object one for each field of TChannelParameter record. So then you can use these properties getter or setter method to Access items in your array.

Unfortunately I can't write you a code example righht now since I'm not on my development computer.