I finally got the data to return itself to this.componentName.
Therefore I am using "that" and added a second variable to the function. The first that is used for the setter is in the meanwhile deactivated through an if statement.
that.componentName(false,data);
Now to avoid an endless loop I check in the main this.componentName call if it's the first or second call with the real data inside.
Now - I still have the problem that the return data is not returned in the way other components like a textview could use it. (with getComponentName) My guess is that the first call gets returned, then the textview receives the data and then the second call starts which returns but the component doesn't starting a second receiving.
Do I need to fire another firePropertiesChanged(["componentName"]); event? If yes - Where?
Right now I am using the firePropertiesChanged in the AfterUpdate.
But I couldn't use it in the callback(processData). In the callback(processData) I can only call that.componentName() but no further events.