iOs add multiple resolution in-app icon

Hello,

i already have setup a bundle of Application icons for multiple devices in order to support devices with different solutions.
This worked quite well, but i cannot figure out how to use this technique also in in-app icons.

To make this clearer lets say you open up the "Music"-Application on an iPhone by pressing the "Application Icon". After that
you have multiple more icons WITHIN your application which also have to support multiple resolution for different devices.
How can i achive this in Qt, or do I have to do this step in Xcode?

e.g set an multiple resulution Icon to an Action

Code:

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myAction->setIcon(QIcon(":/icons/in_app_icon.png"));   //This (of cause) results in an icon with a fixed resultion even if in_app_icon@2x.png ... are present

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Thank you in advance.