message默认显示是居中，现在需要修改为左对齐样式：
利用runtime获取UIAlertController的属性：

        unsigned int count = 0;
        
        Ivar *property = class_copyIvarList([UIAlertController class], &count);
        
        for (int i = 0; i < count; i++) {
            
            Ivar var = property[i];
            
            const char *name = ivar_getName(var);
            
            const char *type = ivar_getTypeEncoding(var);
            
            NSLog(@"%s ====== %s",name,type);
            
        }

可以设置message富文本（左对齐、字体、颜色）：

        NSMutableAttributedString *alertControllerMessageStr = [[NSMutableAttributedString alloc] initWithString:message];
        NSMutableParagraphStyle *paragraph = [[NSMutableParagraphStyle alloc] init];
        paragraph.alignment = NSTextAlignmentLeft;
        [alertControllerMessageStr setAttributes:@{NSParagraphStyleAttributeName:paragraph} range:NSMakeRange(0, alertControllerMessageStr.length)];
  

利用runtime获取到属性：attributedMessage。使用KVO修改message文字样式对齐方式：

[alertContro setValue:alertControllerMessageStr forKey:@"attributedMessage"]

效果图