实例解析C++/CLI的串行化

处理多个句柄

　　当我们传递一个对象的句柄给Serialize时，似乎会在底层对对象进行一个复制，那么，实际情况真的是这样吗？假设我们把包含有多个句柄的一个对象写入到其他对象中，或者我们调用Serialize两次，每次都给它同一个对象的句柄呢？我们真的想得到同一对象的多个副本吗？在例4中演示了这个过程：

　　例4：

using namespace System; using namespace System::IO; using namespace System::Runtime::Serialization::Formatters::Binary; /*1*/ [Serializable] ref class Employee { /* ... */}; int main() { 　Employee^ emp1 = gcnew Employee(); 　Employee^ emp2 = gcnew Employee(); 　Employee^ emp3 = emp2; 　/*2a*/ Console::WriteLine("emp1 == emp2 is {0}", (emp1 == emp2)); 　/*2b*/ Console::WriteLine("emp2 == emp3 is {0}", (emp2 == emp3)); 　/*2c*/ Console::WriteLine("emp1 == emp3 is {0}", (emp1 == emp3)); 　array<Object^>^ list = gcnew array<Object^>(2); 　list[0] = emp1; 　list[1] = list[0]; 　/*2d*/ Console::WriteLine("list[0] == list[1] is {0}", (list[0] == list[1])); 　/*2e*/ Console::WriteLine("list[0] == emp1 is {0}", (list[0] == emp1)); 　/*2f*/ Console::WriteLine("list[1] == emp1 is {0}", (list[1] == emp1)); 　//将数据串行化到文件 　BinaryFormatter^ formatter = gcnew BinaryFormatter; 　Stream^ file = File::Open("Sr03.ser", FileMode::Create); 　/*3a*/ formatter->Serialize(file, emp1); 　/*3b*/ formatter->Serialize(file, emp2); 　/*3c*/ formatter->Serialize(file, emp3); 　/*3d*/ formatter->Serialize(file, list); 　file->Close(); 　//从文件中反串行化数据--即读取数据 　file = File::Open("Sr03.ser", FileMode::Open); 　/*4a*/ emp1 = static_cast<Employee^>(formatter->Deserialize(file)); 　/*4b*/ emp2 = static_cast<Employee^>(formatter->Deserialize(file)); 　/*4c*/ emp3 = static_cast<Employee^>(formatter->Deserialize(file)); 　/*4d*/ list = static_cast<array<Object^>^>(formatter->Deserialize(file)); 　file->Close(); 　/*5a*/ Console::WriteLine("emp1 == emp2 is {0}", (emp1 == emp2)); 　/*5b*/ Console::WriteLine("emp2 == emp3 is {0}", (emp2 == emp3)); 　/*5c*/ Console::WriteLine("emp1 == emp3 is {0}", (emp1 == emp3)); 　/*5d*/ Console::WriteLine("list[0] == list[1] is {0}", (list[0] == list[1])); 　/*5e*/ Console::WriteLine("list[0] == emp1 is {0}", (list[0] == emp1)); 　/*5f*/ Console::WriteLine("list[1] == emp1 is {0}", (list[1] == emp1)); }

　　在本例中，我们想对Employee类型（在标记1中的用户自定义类型）的对象进行串行化，必须把Serializable属性附加到这个类型上。如果我们试图串行化一个没有标明此属性的类对象，将会抛出一个System::Runtime::Serialization::SerializationException类型的异常。串行化之前的程序输出如插3所示：

　　插3：串行化之前例4的输出

emp1 == emp2 is False emp2 == emp3 is True emp1 == emp3 is False list[0] == list[1] is True list[0] == emp1 is True list[1] == emp1 is True

　　我们对四个目标进行了串行化，前两个代表了不同的Employee对象，而第三个是对第二个的引用，第四个为包含两个元素的数组，这两个元素均引用第一个Employee对象。程序的输出表明了它们之间的这些关系，反串行化之后的输出见插4：

　　插4：反串行化之后例4的输出

emp1 == emp2 is False emp2 == emp3 is False emp1 == emp3 is False list[0] == list[1] is True list[0] == emp1 is False list[1] == emp1 is False

　　注意，现在第三个Employee句柄已不再是一个指向第二个Employee对象的句柄了，类似地，尽管list[0]与list[1]都引用同一个Empolyee对象，但对象已不是我们取回的第一个对象了。

　　在此应看到，当多个对象逐个串行化之后，它们是相关联的，而当反串行化之后，它们的关系并没有因此而恢复，但是，对象内部的关系仍然被维持。