闲话少说 看代码(利用最小线高度来设置对齐)
NSMutableParagraphStyle *style = [cell.textField.defaultTextAttributes[NSParagraphStyleAttributeName] mutableCopy];
style.minimumLineHeight = cell.textField.font.lineHeight - (cell.textField.font.lineHeight - [UIFont systemFontOfSize:14.0].lineHeight) / 2.0;
cell.textField.attributedPlaceholder = [[NSAttributedString alloc] initWithString:@"Placeholder text" attributes:@{NSFontAttributeName: [UIFont systemFontOfSize:14.0] ,NSParagraphStyleAttributeName:style}];