Board index » cppbuilder » TListView: How do I save the Data associated with each item?

2005-01-28 07:45:42 AM
cppbuilder91
I've read the post from Gambit regarding how to save the listview
information and it all works beautifully. However, I am also using
the Data property for each Item and have associated data of varying
size. Is there a simple way to figure out the size of the data so
I can save it to disk? Or, better yet, is there a simple way to
save the Data piece of each TListItem?
 

"Brian" < XXXX@XXXXX.COM >wrote in message
indicating how large the size is. For example:
struct Header
{
DWORD size;
// other common values here...
};
struct A
{
Header hdr;
// A-related values here...
A() { hdr.size = sizeof(A); }
};
struct B
{
Header hdr;
// B-related values here...
B() { hdr.size = sizeof(B); }
};
TListItem *Item = ListView1->Items->Add();
//...
Item->Data = new A;
Item = ListView1->Items->Add();
//...
Item->Data = new B;
//...
int count = ListView1->Items->Count;
for(int x = 0; x < count; ++x)
{
Header *pHdr = (Header*) ListView1->Items->Item[x]->Data;
ShowMessage("Item["+AnsiString(x)+"]->Data is
"+AnsiString(pHdr->size)+" bytes in size");
}
If you need to actually know what data type is stored in the Data, then you
have two options:
1) include an enum in the header that specfies what type is bein used:
enum StructType { stA, stB };
struct Header
{
DWORD size;
StructType type;
// other common values here...
};
struct A
{
Header hdr;
// A-related values here...
A() { hdr.size = sizeof(A); hdr.type = stA; }
};
struct B
{
Header hdr;
// B-related values here...
B() { hdr.size = sizeof(B); hdr.type = stB; }
};
int count = ListView1->Items->Count;
for(int x = 0; x < count; ++x)
{
Header *pHdr = (Header*) ListView1->Items->Item[x]->Data;
ShowMessage("Item["+AnsiString(x)+"]->Data is
"+AnsiString(pHdr->size)+" bytes in size");
if( pHdr->type == stA )
{
A *a = (A*) Header;
//use a as needed..
}
else if( pHdr->type == stB )
{
B *b = (B*) Header;
// use b as needed..
}
}
2) derive the types from a common base class and then use polymorphism:
struct Base
{
virtual DWORD getSize() = 0;
// other common stuff here...
};
struct A : public Base
{
// A-related values here...
DWORD getSize() { return sizeof(A); }
};
struct B : public Base
{
// B-related values here...
DWORD getSize() { return sizeof(B); }
};
int count = ListView1->Items->Count;
for(int x = 0; x < count; ++x)
{
Base *pBase = (Base*) ListView1->Items->Item[x]->Data;
ShowMessage("Item["+AnsiString(x)+"]->Data is
"+AnsiString(pBase->getSize())+" bytes in size");
if( A *a = dynamic_cast<A*>(pBase) )
{
// use a as needed..
}
else if( B *b = dynamic_cast<B*>(pBase) )
{
// use b as needed..
}
}
The Data property is just a void* pointer. Only your own code will know how
to interpret it properly.
Gambit