Since you don't bother to tell us what the error messages are, how are we supposed to give you any help?

I will point out at least one other serious error in your code: The constructor for your "Levels" calss is wrong and should be:

Qt Code: 
  1. Levels::Levels( QWidget * parent )
  2. : QMainWindow( parent )
  3. {
  4. }
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In addition, the "bilder" variable is defined incorrectly. It should be QList<QString>, not QList<QString *>. This will cause compiler errors in the "setzeBilder" function because QString::fromStdString() returns a QString, not a QString *.

And why does your "erzeugen()" method have a Levels * argument that is never used? Looks to me like you don't understand how to create and initialize a QWidget-based class. Everything that you are doing in these two extra methods should be called from your class constructor, not externally, like this:

Qt Code: 
  1. Levels::Levels( QWidget * parent )
  2. : QMainWindow( parent )
  3. {
  4.     setzeBilder();
  5.     erzeugen();  // Note, "Levels *" argument is unnecessary and is removed.
  6. }
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And there are probably 6 or 7 more serious errors and memory leaks in your code as well which I will let you discover on your own.

Is there a way to set the list at the class where this class is called?
I have no idea what this question means.