How to add extra data to a tree item?

Question

I'm trying to add extra data to a wx Tree Item using wxTreeItemData, but I cannot construct a wxTreeItemData object, because the constructor doesn't have any parameters.

Here is my sample code:

wxTreeCtrl treeCtrl = new wxTreeCtrl(parentWindow);
treeCtrl->AddRoot("Root");
treeCtrl->AppendItem(root, "item", -1,-1, "some extra data");
/** Signature help for inline ​​​wxTreeItemId​ ​‌​​AppendItem​(const ​​​wxTreeItemId​ &​​‌parent​, const ​​​wxString​ &​​‌text​, int ​​‌image​ = -1, int ​​‌selImage​ = -1, ​​​wxTreeItemData​ *​​‌data​ = (​​​wxTreeItemData​ *)0). Summary: insert a new item in as the last child of the parent. Current parameter 3 of 5: , . **/

This gives me an error:

E0413. no suitable conversion function from "std::string" to "wxTreeItemData *" exists  

But when I pass a wxTreeItemData object nothing happens, because the object is empty.

The wxTreeItemData constructor is without any parameters!

Does anyone know how to add data to a wxTreeItemData object?

Another try

I declared a new class that is derived from the `wxTreeItemData` class, then added a string that will hold the data, and then, I declared, and defined a method to return the data. Code sample:

wxTreeItemId item = treeCtrl->AppendItem(Root, "item", -1,-1, new DataItem("some extra data"));
// It should set the new DataItem object as a wxTreeItemData
// I'll try to get the data object from the TreeCtrl:
DataItem *data = treeCtrl->GetItemData(item);
// Signature help for virtual ​​​wxTreeItemData​ * ​‌​​GetItemData​(const ​​​wxTreeItemId​ &​​‌item​) const.
// Trying to print the data:
std::cout << data->GetData();
// It should print the data.

Error:

E0144. a value of type "wxTreeItemData *" cannot be used to initialize an entity of type "DataItem *"

Because the method GetItemData() returns a wxTreeItemData object. And if I tried to replace the DataItem to wxTreeItemData, I cannot invoke the GetData() method of my DataItem object.

Helpful resources:

[wxWidgets: wxTreeCtrl Class Reference][1]

wxWidgets: wxTreeItemData Class Reference

Answer 1

You indeed need to derive your class from wxTreeItemData, as you've done, and you need to cast the returned value of GetItemData() to the correct value, i.e. write

DataItem *data = static_cast<DataItem*>(treeCtrl->GetItemData(item));

This is safe as long as you only pass actual DataItem objects (and not something else) to SetItemData().