proxy.c

design_patterns code设计模式书中的源码 对学习设计模式的人很有帮助的

/*
*/
#include "Geom.H"
class Event;

#ifdef Implementation
class Image {
  public:
    virtual void Draw(const Point&);
};

/*
*/
class Image;
extern Image* LoadAnImageFile(const char*);
    // external function
/*
*/
class ImagePtr {
public:
    ImagePtr(const char* imageFile);
    virtual ~ImagePtr();
/*
*/
    virtual Image* operator->();
    virtual Image& operator*();
private:
    Image* LoadImage();
private:
    Image* _image;
    const char* _imageFile;
};
/*
*/
ImagePtr::ImagePtr (const char* theImageFile) {
    _imageFile = theImageFile;
    _image = 0;
}
/*
*/
Image* ImagePtr::LoadImage () {
    if (_image == 0) {
        _image = LoadAnImageFile(_imageFile);
    }
    return _image;
}
/*
*/
Image* ImagePtr::operator-> () {
    return LoadImage();
}
/*
*/
Image& ImagePtr::operator* () {
    return *LoadImage();
}
/*
*/
void dummy () {
/*
*/
ImagePtr image = ImagePtr("anImageFileName");
image->Draw(Point(50, 100));  
    // (image.operator->())->Draw(Point(50, 100))
/*
*/
}
/*
*/
#endif
/*
*/
#ifdef SampleCode
#include "iostream.h"
#include "strings.h"
/*
*/
class Graphic {
public:
    virtual ~Graphic();
/*
*/
    virtual void Draw(const Point& at) = 0;
    virtual void HandleMouse(Event& event) = 0;
/*
*/
    virtual const Point& GetExtent() = 0;
/*
*/
    virtual void Load(istream& from) = 0;
    virtual void Save(ostream& to) = 0;
protected:
    Graphic();
};
/*
*/
class Image : public Graphic {
public:
    Image(const char* file);  // loads image from a file
    virtual ~Image();
/*
*/
    virtual void Draw(const Point& at);
    virtual void HandleMouse(Event& event);
/*
*/
    virtual const Point& GetExtent();
/*
*/
    virtual void Load(istream& from);
    virtual void Save(ostream& to);
private:
    // ...
};
/*
*/
class ImageProxy : public Graphic {
public:
    ImageProxy(const char* imageFile);
    virtual ~ImageProxy();
/*
*/
    virtual void Draw(const Point& at);
    virtual void HandleMouse(Event& event);
/*
*/
    virtual const Point& GetExtent();
/*
*/
    virtual void Load(istream& from);
    virtual void Save(ostream& to);
protected:
    Image* GetImage();
private:
    Image* _image;
    Point _extent;
    char* _fileName;
};
/*
*/
ImageProxy::ImageProxy (const char* fileName)  {
    _fileName = strdup(fileName);
    _extent = Point::Zero;  // don't know extent yet
    _image = 0;
}

Image* ImageProxy::GetImage() {
    if (_image == 0) {
        _image = new Image(_fileName);
    }
    return _image;
}
/*
*/
const Point& ImageProxy::GetExtent () {
    if (_extent == Point::Zero) {
        _extent = GetImage()->GetExtent();
    }
    return _extent;
}
/*
*/
void ImageProxy::Draw (const Point& at) {
    GetImage()->Draw(at);
}
/*
*/
void ImageProxy::HandleMouse (Event& event) {
    GetImage()->HandleMouse(event);
}
/*
*/
void ImageProxy::Save (ostream& to) {
    to << _extent << _fileName;
}
/*
*/
void ImageProxy::Load (istream& from) {
    from >> _extent >> _fileName;
}
/*
*/
class TextDocument {
public:
    TextDocument();

    void Insert(Graphic*);
    // ...
};
/*
*/
void dummy () {
/*
*/
TextDocument* text = new TextDocument;
// ...
text->Insert(new ImageProxy("anImageFileName"));
/*
*/
}
/*
*/
#endif
/*
*/