3: What is the application of characteristics and characteristics

Preface

Yes, you read that right, this is a pure English headline article. Skin it.

What are characteristics?

1. Attribute is actually a class, which is directly/indirectly inherited from Attribute.
2. By convention, it ends with Attribut, and is wrapped with [] when marking, and the Attribut at the end can be omitted;

what does attribute can do？

那么特性可以做什么呢？
1.特性：可以增加额外信息，增加额外功能；说人话就是在类的上边用[]括起来，里边写一个类。然后会在创建类对象的时候把特性的类也实例。
Tips:特性不可直接调用。可利用反射技术来调用。也许还有其它，我没有学到。
2.特性的一个小例子可实现程序的高扩展与统一的性质。只需要把属特性的内容修改。就可实现功能。

So how do you use features so awesome?

Don't talk about Sao; go to the teacher code.
Why not upload my code? Because my code is quite awesome (usually I finish writing the blog first and sort out the knowledge before doing code exercises.)

1 main instance call code

//特性增加额外功能；
StudentVip vip = new StudentVip() {
    
     Id = 10000, Name = "lny", QQ = "773984283", MobileNum = 12345678978 };
//在做各位，QQ位数是多少？ 据我所致：QQ位数是以10000开头；
//如果说我们在新增数据到数据库中去的时候，QQ的长度是有限制的  位数：5位数<=QQ<=12位数
//if (!string.IsNullOrWhiteSpace(vip.QQ)&& vip.QQ.Length>=5 && vip.QQ.Length<=12)
//{
    
    

//}
手机号是11位
//if (true)
//{ 
//}

bool bResult = ValidateAttributeExtension.Validate<StudentVip>(vip);

上边代码我进行下讲解。StudentVip这个类，被实例化一下，里边有很多信息。qq呀，手机号呀，如果这些数据直接保存肯定不行。咱们得校验下是否合法。那么调用了下ValidateAttributeExtension类中的静态方法Validate。下边上ValidateAttributeExtension类。

2 Encapsulation class called

public class ValidateAttributeExtension
{
    
    
    public static bool Validate<T>(T t)
    {
    
     
        Type type = t.GetType();
        foreach (PropertyInfo prop in type.GetProperties())
        {
    
    
            // 验证手机号长度
            if (prop.IsDefined(typeof(MobileNumAtrribute), true))
            {
    
    
                object oValue = prop.GetValue(t);
                MobileNumAtrribute atrribute = prop.GetCustomAttribute<MobileNumAtrribute>(true);
                if (!atrribute.Validate(oValue))
                {
    
    
                    return false;
                }
            }

        }
        return true;
    }
}

上边实现了传来的StudentVip的手机号的验证。

1. Get the type of the passed class first.
2. Traversing the attributes is the parameter of {get; set; }.
3. Determine whether the current attribute contains the characteristics of the mobile phone number verification class.
4. Get the current mobile phone number value.
5. Get the instance of the feature, and then call the Validate method.

3. The MobileNumAtrribute class.

public class MobileNumAtrribute : AbstractValidateAttribute
{
    
    
    public int Count {
    
     get; private set; }

    public MobileNumAtrribute(int count)
    {
    
    
        if (count<=0)
        {
    
    
            throw new Exception("手机号长度不可能为负数");
        }
        Count = count;
    }

    public override bool Validate(object mobileNum)
    {
    
     
        return mobileNum != null && mobileNum.ToString().Length == Count;
        //if (mobileNum != null && mobileNum.ToString().Length == Count)
        //{
    
    
        //    return true;
        //}
        //else
        //{
    
    
        //    return false;
        //}
    }

}

MobileNumAtrribute继承自AbstractValidateAttribute的原因是因为AbstractValidateAttribute为抽象类，这样可以用一个实例来调用他的子集，说到这你是不是能想到2应该替换成什么样呢？

//如果后续还需要再加一个验证呢？那岂不是 又要修改代码？
//这样做是坑，抽象~~ 
if (prop.IsDefined(typeof(AbstractValidateAttribute), true))
{
    
    
    object oValue = prop.GetValue(t);
    AbstractValidateAttribute atrribute = prop.GetCustomAttribute<AbstractValidateAttribute>(true);
    if (!atrribute.Validate(oValue))
    {
    
    
        return false;
    }
}

Next for the display of feature calls

public class StudentVip : Student
{
    
    
    [QQAttribute(_MinLenth = 5, _MaxLenth = 12)]
    public string QQ {
    
     get; set; }

    [MobileNumAtrribute(11)]
    public long MobileNum {
    
     get; set; }
}

 1. [MobileNumAtrribute(11)]这块就是给MobileNum属性增加了一个特性。调用类的有参构造函数，给Count赋值11位
 2. 接下来就可以在使用的时候调用Validate来验证长度是否合法。

Class is over