Ok i found it ! you have to export your XD file in PDF, after that you go on Affinity, click on your PDF file in order to open it and you export it on PSD format. At the end, you go on avocode.com and you convert your PSD file into a Sketch file. Here you have the link :
avocode.com/convert-psd-to-sketch
for more details i watched these two videos on youtube :
Ok i found it ! you have to export your XD file in PDF, after that you go on Affinity, click on your PDF file in order to open it and you export it on PSD format. At the end, you go on avocode.com and you convert your PSD file into a Sketch file. Here you have the link :
avocode.com/convert-psd-to-sketch
for more details i watched these two videos on youtube :
https://bit.ly/2WIOhb1
https://bit.ly/2VbyEIP
This is the only way for me where it's works.