wxList classes provide linked list functionality for wxWidgets, and for an application if it wishes. Depending on the form of constructor used, a list can be keyed on integer or string keys to provide a primitive look-up ability, but please note that this feature is deprecated. See wxHashMap for a faster method of storage when random access is required.
While wxList class in the previous versions of wxWidgets only could contain elements of type wxObject and had essentially untyped interface (thus allowing you to put apples in the list and read back oranges from it), the new wxList classes family may contain elements of any type and has much more strict type checking. Unfortunately, it also requires an additional line to be inserted in your program for each list class you use (which is the only solution short of using templates which is not done in wxWidgets because of portability issues).
The general idea is to have the base class wxListBase working with void * data but make all of its dangerous (because untyped) functions protected, so that they can only be used from derived classes which, in turn, expose a type safe interface. With this approach a new wxList-like class must be defined for each list type (i.e. list of ints, of wxStrings or of MyObjects). This is done with WX_DECLARE_LIST and WX_DEFINE_LIST macros like this (notice the similarity with WX_DECLARE_OBJARRAY and WX_IMPLEMENT_OBJARRAY macros):
Example
// this part might be in a header or source (.cpp) file
class MyListElement
{
... // whatever
};
// declare our list class: this macro declares and partly implements MyList
// class (which derives from wxListBase)
WX_DECLARE_LIST(MyListElement, MyList);
...
// the only requirement for the rest is to be AFTER the full declaration of
// MyListElement (for WX_DECLARE_LIST forward declaration is enough), but
// usually it will be found in the source file and not in the header
#include <wx/listimpl.cpp>
WX_DEFINE_LIST(MyList);
// now MyList class may be used as a usual wxList, but all of its methods
// will take/return the objects of the right (i.e. MyListElement) type. You
// also have MyList::Node type which is the type-safe version of wxNode.
MyList list;
MyListElement element;
list.Append(element); // ok
list.Append(17); // error: incorrect type
// let's iterate over the list
for ( MyList::Node *node = list.GetFirst(); node; node = node->GetNext() )
{
MyListElement *current = node->GetData();
...process the current element...
}
For compatibility with previous versions wxList and wxStringList classes are
still defined, but their usage is deprecated and they will disappear in the
future versions completely. The use of the latter is especially discouraged as
it is not only unsafe but is also much less efficient than
wxArrayString class.In the documentation of the list classes below, the template notations are used even though these classes are not really templates at all -- but it helps to think about them as if they were. You should replace wxNode<T> with wxListName::Node and T itself with the list element type (i.e. the first parameter of WX_DECLARE_LIST).
Derived from
Include files
<wx/list.h>
Example
It is very common to iterate on a list as follows:
...
wxWindow *win1 = new wxWindow(...);
wxWindow *win2 = new wxWindow(...);
wxList SomeList;
SomeList.Append(win1);
SomeList.Append(win2);
...
wxNode *node = SomeList.GetFirst();
while (node)
{
wxWindow *win = node->GetData();
...
node = node->GetNext();
}
To delete nodes in a list as the list is being traversed, replace
...
node = node->GetNext();
...
with
...
delete win;
delete node;
node = SomeList.GetFirst();
...
See wxNode for members that retrieve the data associated with a node, and
members for getting to the next or previous node.See also
Members
wxList::wxList
wxList::~wxList
wxList::Append
wxList::Clear
wxList::DeleteContents
wxList::DeleteNode
wxList::DeleteObject
wxList::Erase
wxList::Find
wxList::GetCount
wxList::GetFirst
wxList::GetLast
wxList::IndexOf
wxList::Insert
wxList::IsEmpty
wxList::Item
wxList::Member
wxList::Nth
wxList::Number
wxList::Sort
wxList()
wxList(int n, T *objects[])
wxList(T *object, ...)
Note: keyed lists are deprecated and should not be used in new code.
wxList(unsigned int key_type)
Constructors. key_type is one of wxKEY_NONE, wxKEY_INTEGER, or wxKEY_STRING, and indicates what sort of keying is required (if any).
objects is an array of n objects with which to initialize the list.
The variable-length argument list constructor must be supplied with a terminating NULL.
~wxList()
Destroys the list. Also destroys any remaining nodes, but does not destroy client data held in the nodes.
wxNode<T> * Append(T *object)
Note: keyed lists are deprecated and should not be used in new code.
wxNode<T> * Append(long key, T *object)
wxNode<T> * Append(const wxString& key, T *object)
Appends a new wxNode to the end of the list and puts a pointer to the object in the node. The last two forms store a key with the object for later retrieval using the key. The new node is returned in each case.
The key string is copied and stored by the list implementation.
void Clear()
Clears the list (but does not delete the client data stored with each node unless you called DeleteContents(true), in which case it deletes data).
void DeleteContents(bool destroy)
If destroy is true, instructs the list to call delete on the client contents of a node whenever the node is destroyed. The default is false.
bool DeleteNode(wxNode<T> *node)
Deletes the given node from the list, returning true if successful.
bool DeleteObject(T *object)
Finds the given client object and deletes the appropriate node from the list, returning true if successful. The application must delete the actual object separately.
void Erase(wxNode<T> *node)
Removes element at given position.
wxNode<T> * Find(T * object)
Returns the node whose client data is object or NULL if none found.
Note: keyed lists are deprecated and should not be used in new code.
wxNode<T> * Find(long key)
wxNode<T> * Find(const wxString& key)
Returns the node whose stored key matches key. Use on a keyed list only.
size_t GetCount() const
Returns the number of elements in the list.
wxNode<T> * GetFirst()
Returns the first node in the list (NULL if the list is empty).
wxNode<T> * GetLast()
Returns the last node in the list (NULL if the list is empty).
int IndexOf(T* obj )
Returns the index of obj within the list or wxNOT_FOUND if obj is not found in the list.
wxNode<T> * Insert(T *object)
Insert object at front of list.
wxNode<T> * Insert(size_t position, T *object)
Insert object before position, i.e. the index of the new item in the list will be equal to position. position should be less than or equal to GetCount; if it is equal to it, this is the same as calling Append.
wxNode<T> * Insert(wxNode<T> *node, T *object)
Inserts the object before the given node.
bool IsEmpty() const
Returns true if the list is empty, false otherwise.
wxNode<T> * Item(size_t index) const
Returns the node at given position in the list.
wxNode<T> * Member(T *object)
NB: This function is deprecated, use Find instead.
Returns the node associated with object if it is in the list, NULL otherwise.
wxNode<T> * Nth(int n)
NB: This function is deprecated, use Item instead.
Returns the nth node in the list, indexing from zero (NULL if the list is empty or the nth node could not be found).
int Number()
NB: This function is deprecated, use GetCount instead.
Returns the number of elements in the list.
void Sort(wxSortCompareFunction compfunc)
// Type of compare function for list sort operation (as in 'qsort') typedef int (*wxSortCompareFunction)(const void *elem1, const void *elem2);Allows the sorting of arbitrary lists by giving a function to compare two list elements. We use the system qsort function for the actual sorting process.
If you use untyped wxList the sort function receives pointers to wxObject pointers (wxObject **), so be careful to dereference appropriately - but, of course, a better solution is to use list of appropriate type defined with WX_DECLARE_LIST.
Example:
int listcompare(const void *arg1, const void *arg2)
{
return(compare(**(wxString **)arg1, // use the wxString 'compare'
**(wxString **)arg2)); // function
}
void main()
{
wxList list;
list.Append(new wxString("DEF"));
list.Append(new wxString("GHI"));
list.Append(new wxString("ABC"));
list.Sort(listcompare);
}