如何在托管C ++中使用手写的getter / setter定义属性？

Question

I need to define properties with handwritten getters/setters in a managed C++ project, in a class that will be usable from a C# .NET project.

• The codeproject article on the subject recommends the __property float Volume; which is outdated and now classified as /crl:oldSyntax .

• The Open Standard managed extensions to C++ article says that defining properties like property float Volume; automatically generate a backing field, which I don't want or need.

• Simply defining properties like property float Volume; compiles fine with /clr , but attempting to add handwritten getters/setters like float Mixer::Volume::get(){ .. } throw Error C2084: function X already has a body .

So what is the proper way to define read-only or read/write properties without a backing field, and with custom-built handwritten getter/setter methods?

Answer 1

You have found the header-only version by yourself. If you want to implement the getters and setters in a cpp file, the syntax is as follows:

///////////////////////
// Foo.h:
///////////////////////
ref struct Foo
{ 
    property float Volume
    {
        float get();
        private: void set(float value);
    }
private:
    float m_backingField;
}

///////////////////////
// Foo.cpp:
///////////////////////
float Foo::Volume::get()
{
    return m_backingField;
}

void Foo::Volume::set(float value)
{
    m_backingField = value;
}

Edit: Some additional information :

• You can specify different access modifiers for the getter and the setter. I modified the source code in order to make the setter private. Note that unlike in C# this is not possible if you use the automatic generation of backing store.
• What was called "managed extensions for C++" earlier, is now (starting with Visual Studio 2005) called C++/CLI. It is not only a renaming but a complete new revision. The double underscore __property keyword came from the managed extensions and is now deprecated.

Answer 2

Well I found you have to declare the property only ONCE in the header file, as follows:

property float Volume {
    float get() {
        return 0;
    }
    void set(float value) {
    }
}

If you declare the property like the follows, a backing field is automatically generated:

property float Volume;