some question about sbutton a long time ,stil cant find the api (Advanced_SetDesiredSize seem to no effect ),any tips

2.i write some snippe code to do the test of create image brush ,no image show. how to find the bug?
static FButtonStyle lBtStyle;
FString lDir = FPaths::GameContentDir() / “08.png”;
lBtStyle.SetNormal(FSlateImageBrush(lDir, FVector2D(100, 100)));

thanks for any tips .