如何在属性属性上使用条件语句IF ELSE

Question

I want to show MyProperty1 or MyProperty2 based on MyPropertySelected . How to use a conditional statement if or else based on MyPropertySelected ? Thanks.

// [Browsable(true)
// ????? conditional statement IF ELSE in here..
// IF (MyPropertySelected) MyProperty1 will be show ELSE MyProperty2 will be show.
public bool MyPropertySelected { get; set; }

// [Browsable(true) or [Browsable(false) depending on MyPropertySelected condition.
public int MyProperty1 { get; set; }

// [Browsable(true) or [Browsable(false) depending on MyPropertySelected condition.
public int MyProperty2 { get; set; }

Answer 1

You're confusing apples with oranges.

Attributes are metadata and a property value acquires its value on run-time.

In other words: attribute is something that you'll access using reflection and those aren't tied to a particular object but to the type of the object (ie the class ).

Another issue is that you want to add an attribute to a property based on a condition that can't work in compile-time.

Your MyPropertySelected won't get any value until its enclosing class gets instantiated - that's creating an object, for example: MyClass a = new MyClass() - , meaning that adding or not adding the attribute would never be a compile-time choice .

I want to be clear: you can't do what you want purely using attributes!

You can't conditionally apply attributes based on run-time values .

Finally, I suspect you want to make something Browsable based on a condition, like your own question says. You can't do that.

Ok ok, but what...?

You can workaround your situation with a different software design.

1)

First, create an interface that will have any of the properties that would be browsable or not. But don't apply the attribute [Browsable(bool)] to the interface properties.

2)

Create two classes that implements the previously created interface.

In the first class, implement the interface properties and put a [Browsable(true)] attribute on them. In the second class, do the same, but this time put a [Browsable(false)] on them.

3)

Some code that creates the instance of the object will be the one that will also decide which one will be instantiated .

That is, externalizing MyPropertySelected outside of both classes and performing the whole condition switch in the caller.

public interface IBrowsableProperties
{
   int Property1 { get;set; }
   int Property2 { get;set; }
}

public class A : IBrowsableProperties
{ 
   [Browsable(true)]
   public int Property1 { get;set; }

   [Browsable(true)]
   public int Property1 { get;set; }
}

public class B : IBrowsableProperties
{
   [Browsable(false)]
   public int Property1 { get;set; }

   [Browsable(false)]
   public int Property1 { get;set; }
}

// Somewhere in some method...
bool propertySelected = true;

IBrowsableProperties instance = null;

if(propertySelected) 
{
   instance = new A();
}
else
{
   instance = new B();
}

// ... do stuff with your instance of IBrowsableProperties!

UPDATE

I've reviewed some of your question's comments and I've found you're working with PropertyGrid control.

Anyway, you can apply the concept in your case. PropertyGrid can be inherited. You can create both PropertyGrid1 and PropertyGrid2 derived classes that both implement the proposed interface!

Answer 2

You probably want an intermediary property like this:

class Foo
{
    public bool MyPropertySelected
    {
        get;
        set;
    }

    public readonly int MyProperty
    {
        get 
        {
            return MyPropertySelected ? MyProperty1 : MyProperty2;
        }
    }

    private int MyProperty1
    {
        get;
        set;
    }

    private int MyProperty2
    {
        get;
        set;
    }
}