Waiting for a download event

[tbscope]

You have your mind set on a synchronous connection.
While, as stated already, the get() function is asynchronous.

You want to use the finished() signal.
And you need to change the program logic to deal with this. This should not be too hard.
Basically, create a signal in your xmlReader class that fires when the networkaccessmanager finished() signal is fired. Before that, the xmlReader class can do the necessary parsing.
Then connect a slot from your WallPaperselection class to the xmlReader finished signal.
Then use some getter functions to get the needed data.