缘起，看到一遍文章，题材取自于《C++沉思录》，综合利用好几种设计模式，并且结合所谓的面向对象的技巧，然后洋洋自得，并且在最后，还反问：“有更好的解决方案吗？”。本座暗叹，又一个设计模式的毒害者。以下，就提出另一种解决方案。
首先，先声明一点，现实中，一张图片，可以给予添加一层又一层片框，也可以和其他的图片组合在一块，或横，或竖，……，但是，图片，始终只有一张，对它处理之后，它就一直是那个样子了，不可能同时看到它的两个样子，或加边框，或和其他照片组合在一块。如果，拿这张图片去进行复制，那又自是另当别论，但那已经是另外一第图片了。当然，对以下例子稍加修改，就能支持修饰的图片的复制操作。
本座最近在写一套消息框架，如果这个例子能用上那套框架，写起来就会很简单。但是，即使没有消息框架的支持，利用消息发送来解决这个问题，也是相当小儿科的事情。为了突出重点，忽略了各种异常处理，没有优化，也不管什么编程风格，纯粹直奔主题。解决这个例子的最重要一点，就在于打印图片时，要一行一行地从顶到底顺次打印下来。
typedef int (*ProcPictureImp)(void* pThis, int nMessage, void* param1, void* param2);
enum 
{ PM_WIDTH, PM_HEIGHT, PM_PRINT_ROW};
struct PictureImp
{
void* pThis;
ProcPictureImp proc;
int GetWidth()
{
return (*proc)(pThis, PM_WIDTH, NULL, NULL);
}
int GetHeight()
{
return (*proc)(pThis, PM_HEIGHT, NULL, NULL);
}
int PrintRow(int nRow, ostream& out)
{
return (*proc)(pThis, PM_PRINT_ROW, (void*)nRow, (void*)&out);
}
};
class CPicture
{
public:
CPicture(const char* pDatas[], int nCount)
{
m_pDatas = pDatas;
m_nCount = nCount;
m_nWidth = 0;
for (int i=0; i<m_nCount; i++)
{
int nLen = strlen(m_pDatas[i]);
if (m_nWidth < nLen)
m_nWidth = nLen;
}
m_Imp.pThis = this;
m_Imp.proc = HandleMsg;
}
void Print(ostream& out);
public:
PictureImp m_Imp;
private:
const char** m_pDatas;
int m_nCount;
int m_nWidth;
static int HandleMsg(void* pThis, int nMessage, void* param1, void* param2);
};
int CPicture::HandleMsg(void* pThis, int nMessage, void* param1, void* param2)
{
CPicture* pSelf = (CPicture*)pThis;
switch (nMessage)
{
case PM_WIDTH:
return pSelf->m_nWidth;
case PM_HEIGHT:
return pSelf->m_nCount;
break;
case PM_PRINT_ROW:
int nRow = (int)param1;
ostream& out = *(ostream*)param2;
if (nRow >= pSelf->m_nCount)
break;
int i=0;
for (; pSelf->m_pDatas[nRow][i] != 0; i++)
out << pSelf->m_pDatas[nRow][i];
for (; i<pSelf->m_nWidth; i++)
out << ' ';
}
return 0;
}
void CPicture::Print(ostream& out)
{
int nHeight = m_Imp.GetHeight();
for (int nRow = 0; nRow<nHeight; nRow++)
{
m_Imp.PrintRow(nRow, out);
out << endl;
}
}
class CFrameDecorater
{
public:
CFrameDecorater(PictureImp& imp)
{
m_PrevImp = imp;
imp.pThis = this;
imp.proc = HandleMsg;
}
private:
PictureImp m_PrevImp;
static int HandleMsg(void* pThis, int nMessage, void* param1, void* param2);
};
int CFrameDecorater::HandleMsg(void* pThis, int nMessage, void* param1, void* param2)
{
CFrameDecorater* pSelf = (CFrameDecorater*)pThis;
PictureImp& prevImp = pSelf->m_PrevImp;
switch (nMessage)
{
case PM_WIDTH:
return prevImp.GetWidth()+2;
case PM_HEIGHT:
return prevImp.GetHeight()+2;
case PM_PRINT_ROW:
int nRow = (int)param1;
ostream& out = *(ostream*)param2;
bool bMyRow = nRow == 0 || nRow>prevImp.GetHeight();
if (nRow >= prevImp.GetWidth()+2)
break;
if (nRow == 0 || nRow>prevImp.GetHeight())
{
out << '+';
for (int i=0; i<prevImp.GetWidth(); i++)
out << '-';
out << '+';
}
else
{
out << '|';
prevImp.PrintRow(nRow-1, out);
out << '|';
}
}
return 0;
}
class CHorseDecorater
{
public:
CHorseDecorater(PictureImp& impLeft, PictureImp& impRight)
{
m_Left = impLeft;
m_Right = impRight;
impLeft.pThis = this;
impLeft.proc = HandleMsg;
impRight.pThis = this;
impRight.proc = HandleMsg;
}
private:
PictureImp m_Left;
PictureImp m_Right;
static int HandleMsg(void* pThis, int nMessage, void* param1, void* param2);
static void PrintRow(PictureImp& pict, int nRow, ostream& out)
{
if (nRow < pict.GetHeight())
pict.PrintRow(nRow, out);
else
{
for (int i=0; i<pict.GetWidth(); i++)
out << ' ';
}
}
};
int CHorseDecorater::HandleMsg(void* pThis, int nMessage, void* param1, void* param2)
{
CHorseDecorater* pSelf = (CHorseDecorater*)pThis;
PictureImp& pictLeft = pSelf->m_Left;
PictureImp& pictRight = pSelf->m_Right;
switch (nMessage)
{
case PM_WIDTH:
return pictLeft.GetWidth()+pictRight.GetWidth();;
case PM_HEIGHT:
return max(pictLeft.GetHeight(), pictRight.GetHeight());
case PM_PRINT_ROW:
int nRow = (int)param1;
ostream& out = *(ostream*)param2;
PrintRow(pictLeft, nRow, out);
PrintRow(pictRight, nRow, out);
}
return 0;
}
int main()
{
const char* init1[] = {"Paris", "in the", "Spring", "HaHa"};
CPicture pict1(init1, 3);
pict1.Print(cout);
CFrameDecorater framer1(pict1.m_Imp);
//pict1.Print(cout);
CFrameDecorater framer2(pict1.m_Imp);
pict1.Print(cout);
CPicture pict2(init1, 4);
CHorseDecorater hors(pict1.m_Imp, pict2.m_Imp);
pict1.Print(cout);
CFrameDecorater framerHorse(pict1.m_Imp);
pict1.Print(cout);
return 0;
}
嗯，明眼人一眼就看出来了，切，这不过是模仿WINDOWS的窗口消息处理函数的伎俩而已。没有继承、没有虚函数，何其美妙哉！
又，注意到main()中的代码，虽然pict1被装饰了好几次，但其图片打印，始终都是pict1.Print(cout)。所谓不管八风乱起，我自岿然不动