緣起，看到一遍文章，題材取自于《C++沉思錄》，綜合利用好幾種設計模式，并且結合所謂的面向對象的技巧，然后洋洋自得，并且在最后，還反問：“有更好的解決方案嗎？”。本座暗嘆，又一個設計模式的毒害者。以下，就提出另一種解決方案。
首先，先聲明一點，現實中，一張圖片，可以給予添加一層又一層片框，也可以和其他的圖片組合在一塊，或橫，或豎，……，但是，圖片，始終只有一張，對它處理之后，它就一直是那個樣子了，不可能同時看到它的兩個樣子，或加邊框，或和其他照片組合在一塊。如果，拿這張圖片去進行復制，那又自是另當別論，但那已經是另外一第圖片了。當然，對以下例子稍加修改，就能支持修飾的圖片的復制操作。
本座最近在寫一套消息框架，如果這個例子能用上那套框架，寫起來就會很簡單。但是，即使沒有消息框架的支持，利用消息發送來解決這個問題，也是相當小兒科的事情。為了突出重點，忽略了各種異常處理，沒有優化，也不管什么編程風格，純粹直奔主題。解決這個例子的最重要一點，就在于打印圖片時，要一行一行地從頂到底順次打印下來。
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，明眼人一眼就看出來了，切，這不過是模仿WINDOWS的窗口消息處理函數的伎倆而已。沒有繼承、沒有虛函數，何其美妙哉！
又，注意到main()中的代碼，雖然pict1被裝飾了好幾次，但其圖片打印，始終都是pict1.Print(cout)。所謂不管八風亂起，我自巋然不動