java - Is getChildren() of ContentProvider called before treeExpanded() of ITreeViewerListener? -

i want fetch data if specific element of tree expanded.

public void treeexpanded(treeexpansionevent event) {      object element = event.getelement();    if (element instanceof myclass) {       fetch.......    } }  

the problem content provider seems trigger getchildren() before treeexpanded()-method nullpointerexception everytime expand element because content provider tries use data never fetched. how can solve properly?

your code should not depend on order in getchildren() , treeexpanded() called. implementation detail of treeviewer , may change in future.

fetch elements shown in getchildren() or inputchanged() of content provider.

if fetch operation takes long run in ui thread, run in background thread , return placeholder element replaced, once fetch operation finishes. example, see deferredtreecontentmanager of org.eclipse.ui.

alternatively can see if jface deferredcontentprovider fits needs.