UITextField的占位文字水平居中

UITextField的提示文字水平居中：

NSMutableParagraphStyle *paragraphStyle = NSMutableParagraphStyle.new;

paragraphStyle.alignment = NSTextAlignmentCenter;

self.textField.attributedPlaceholder = [NSAttributedString.alloc initWithString:@"tips"
                                                                     attributes:@{NSParagraphStyleAttributeName:paragraphStyle}];