C＃中的Overload =运算符或在赋值之后和之前触发事件的替代方法？

Question

I'm trying to create my own data type.
So I started with a base example of Microsoft DynamicDictionary .

The code is : at http://msdn.microsoft.com/en-us/library/system.dynamic.dynamicobject.aspx

Main part of my type

public class myDynType : System.Dynamic.DynamicObject
{
    ....
}

Now I want something like this in my code :

[MaxAllowedValue(100)]
myDynType  SomeVar;

As you know we can't overload assignment in C# (= operator) so what are alternative ways to fire a event before assignment and after that ?

SomeVar = 7.55;   // I want to fire an event right before assignment
//Plus after assignment 

I want to check the value before assignment to throw an exception if it's bigger than 100. And I want to check it after assignment to round the value or modify it.

Answer 1

Not exactly, but maybe you can do what you need with properties:

myDynType someVar;
[MaxAllowedValue(100)]
myDynType SomeVar
{
    get
    {
        return someVar;
    }
    set
    {
        PreStuff();
        someVar = value;
        PostStuff();
    }
}

Answer 2

You can accomplish this by overloading the implicit conversion (casting) operator. For instance:

class MyDynType : System.Dynamic.DynamicObject
{
    public int Value { get; set; }
    public static implicit operator MyDynType(int value)
    {
        MyDynType x = new MyDynType();
        if (value > 100)
            x.Value = 100;
        else
            x.Value = value;
        return x;
    }
}

Then you can use it like this:

dynamic x = (MyDynType)6;
Console.WriteLine(x.Value);  // Outputs "6"
dynamic y = (MyDynType)150;           
Console.WriteLine(y.Value);  // Outputs "100"

For more info, see the MSDN page . Since you tagged VB.NET, I'll mention that the equivalent in VB.NET is to overload the CType operator using Widening modifier.

However, overloading the conversion operators can cause a lot of confusion, so you should do so sparingly, if at all.