length of collection inside a function

[AntonioGraca]

Hi

I'm trying to get the collection length value running the service query inside a function. But I'm not getting it because it only takes on the correct value after finishing the function using this code inside of del_lista() function:

this.Apperyio.execDataService(this, "notas_QS5");

Now, Im trying to use this code
execDataService(context: any, serviceName: string, callback?: Function): void

But, I dont know to use correctly...

this.Apperyio.execDataService(this, "notas_QS5", this.del_lista()): void;
This code is inside of del_lista function.

context: any, = this
serviceName: string = "notas_QS5"
callback?: Function = del_lista // what I need put here???
void=?????? what I nee put here???
this.Apperyio.execDataService(this, "notas_QS5", this.del_lista()): void;

Maybe I missing someting here...

Thank you...