【学习笔记】C/C++ 设计模式 - 模板模式
介绍说明
模板设计模式是一种非常简单的设计模式，其主要是利用了虚函数的特性实现。非常适合应用在一些算法、流程、业务逻辑是固定的形式，其中某些步骤的实现方式又无法确定下来的场景。
举例说明
以下为模拟某芯片基于串口通信的固件升级代码，可以提供一个 FirmwareUpgrade 的类用于使用者集成。考虑到跨平台，该类的串口操作接口声明为纯虚函数，由使用者自己根据所用平台实现，而不需要关注具体的升级细节。
class FirmwareUpgrade
{
protected:
// 具体的串口操作实现延迟到子类实现
// 在不同的平台下, 提供对应平台的串口操作实现即可
virtual bool openSerialPort(int nBaudRate, int nDataBit, int nStopBit, int nParityBit) = 0;
virtual bool wrtieSerialPort(void *pOutBuffer, size_t nLength) = 0;
virtual size_t readSerialPort(void *pInBuffer, size_t size) = 0;
virtual bool closeSerialPort() = 0;
public:
FirmwareUpgrade() {};
virtual ~FirmwareUpgrade() {};
// 开始升级
bool upgrade(const char *pFirmwareFile) {
init();
...
enterUpgradeMode();
...
erasePartition();
...
updatePartition(pFirmwareFile);
...
verifyPartition();
...
resetDevice();
...
release();
return true;
}
private:
bool sendCommand(int cmd, void *pdata, size_t size) {
if (!wrtieSerialPort(package, sizeof(package))) {
return false;
}
if(readSerialPort(package, sizeof(package))) {
return false;
}
return package->done;
}
bool init(){
...
if (!openSerialPort(115200, 8, 1, 0)) {
return false;
}
...
return true;
}
bool enterUpgradeMode(){
...
}
bool erasePartition(){
...
}
bool updatePartition(const char *pFirmwareFile){
FILE fp = fopen(pFirmwareFilel, "rb");
...
while (fread(buffer, sizeof(buffer), 1, fp) == 1)
{
if (!sendCommand(update_COMMAND, NULL, 0)) {
fclose(fp);
return false;
}
}
...
fclose(fp);
return true;
}
bool verifyPartition() {
...
}
bool resetDevice(){
...
}
bool release() {
...
return closeSerialPort();
}
};如 Windows 平台开发者，只需要利用 Windows 平台下接口实现串口的打开、写入、读取、关闭四个接口即可：
class FirmwareUpgradeWin : public FirmwareUpgrade
{
private:
virtual bool openSerialPort(int nBaudRate, int nDataBit, int nStopBit, int nParityBit)
{
com_handle = CreateFile("//.//COM9", GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
if (com_handle != INVALID_HANDLE_VALUE){
...
}
...
}
virtual bool wrtieSerialPort(void *pOutBuffer, size_t nLength)
{
if (com_handle != INVALID_HANDLE_VALUE)
{
DWORD NumberOfBytesWrite;
if (!WriteFile(com_handle, buffer, length, &NumberOfBytesWrite, NULL))
{
DWORD error = GetLastError();
printf("error:%d\n", error);
}
return NumberOfBytesWrite;
}
}
virtual size_t readSerialPort(void *pInBuffer, size_t size)
{
if (com_handle != INVALID_HANDLE_VALUE)
{
DWORD NumberOfBytesRead;
ReadFile(com_handle, buffer, length, &NumberOfBytesRead, NULL);
return NumberOfBytesRead;
}
return 0;
}
virtual bool closeSerialPort()
{
// 关闭硬件接口
if (com_handle != INVALID_HANDLE_VALUE)
{
CloseHandle(com_handle);
}
}
public
bool upgrade(const char *pFirmwareFile) {
return FirmwareUpgrade::upgrade(pFirmwareFile);
}
};
int main()
{
FirmwareUpgradeWin mFirmwareUpgrade;
mFirmwareUpgrade.upgrade("d:\\xxxx.bin");
return 0;
}如 Linux 平台下的实现：
class FirmwareUpgradeLinux : public FirmwareUpgrade
{
private:
virtual bool openSerialPort(int nBaudRate, int nDataBit, int nStopBit, int nParityBit)
{
m_fd = ::open(device_node, O_RDWR | O_NOCTTY);
....
tcgetattr(m_fd, &m_options);
....
return true;
}
virtual bool wrtieSerialPort(void *pOutBuffer, size_t nLength)
{
...
byte = write(m_fd, pOutBuffer, nLength));
...
return true;
}
virtual size_t readSerialPort(void *pInBuffer, size_t size)
{
...
select(m_fd + 1, &fs_read, NULL, NULL, &time);
...
byte = read(m_fd, data, size);
...
return byte;
}
virtual bool closeSerialPort()
{
...
close(m_fd);
...
return true
}
public:
bool upgrade(const char *pFirmwareFile) {
return FirmwareUpgrade::upgrade(pFirmwareFile);
}
};
int main()
{
FirmwareUpgradeLinux mFirmwareUpgrade;
mFirmwareUpgrade.upgrade("d:\\xxxx.bin");
return 0;
}总结说明
主要就是将差异化的抽离出来，延迟到子类实现，而固定的逻辑处理则由父类封装并提供接口。相当于定义一个模板，子类只要按照这个模板实现相应的接口，由父类反向调用子类所实现的接口，来完成具体的逻辑功能。这样使用者不需要关心具体的升级逻辑实现，只需要按照要求完成相应的接口，即可使用升级功能，从而降低复杂性，又提升了灵活性。
