iOS 字体斜体

 //里面的参数自己修改吧
CGAffineTransform matrix =  CGAffineTransformMake(1, 0, tanf(15 * (CGFloat)M_PI / 180), 1, 0, 0);
    UIFontDescriptor *desc = [ UIFontDescriptor fontDescriptorWithName :[ UIFont boldSystemFontOfSize:20 ]. fontName matrix :matrix];
    UIFont *font = [ UIFont fontWithDescriptor :desc size :20];