TreeFilterHandler.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreMinimal.h"
#include "Misc/IFilter.h"
#include "Widgets/Views/STreeView.h"
 
template<typename ItemType>
class TreeFilterHandler
{
public:
    typedef typename TSlateDelegates< ItemType >::FOnGetChildren FOnGetChildren;
 
public:
 
    TreeFilterHandler()
    {
        TreeView = nullptr;
        Filter = nullptr;
        RootItems = nullptr;
        TreeRootItems = nullptr;
        bIsEnabled = false;
        bWasEnabled = false;
    }
 
    void SetTreeView(STreeView<ItemType>* InTreeView)
    {
        TreeView = InTreeView;
    }
 
    void SetFilter(IFilter<ItemType>* InFilter)
    {
        Filter = InFilter;
    }
 
    void SetRootItems(TArray<ItemType>* InRootItems, TArray<ItemType>* InTreeRootItems)
    {
        RootItems = InRootItems;
        TreeRootItems = InTreeRootItems;
    }
 
    void SetGetChildrenDelegate(FOnGetChildren InGetChildrenDelegate)
    {
        GetChildrenDelegate = InGetChildrenDelegate;
    }
 
    bool GetIsEnabled()
    {
        return bIsEnabled;
    }
 
    void SetIsEnabled(bool bInIsEnabled)
    {
        bIsEnabled = bInIsEnabled;
    }
 
    void RemoveCachedItem(ItemType ItemToRemove)
    {
        PrefilterExpandedItems.Remove(ItemToRemove);
    }
 
    void RefreshAndFilterTree()
    {
        if (TreeView && Filter && RootItems && TreeRootItems && GetChildrenDelegate.IsBound())
        {
            TreeRootItems->Empty();
            ItemsPassingFilter.Empty();
            if (bIsEnabled)
            {
                if (!bWasEnabled)
                {
                    PrefilterExpandedItems.Empty();
                    TreeView->GetExpandedItems(PrefilterExpandedItems);
                }
                for (auto RootItem : *RootItems)
                {
                    if (ExpandAndCacheMatches(RootItem))
                    {
                        TreeRootItems->Add(RootItem);
                    }
                }
            }
            else
            {
                if (bWasEnabled)
                {
                    TreeView->ClearExpandedItems();
                    for (auto PrefilterExpandedItem : PrefilterExpandedItems)
                    {
                        TreeView->SetItemExpansion(PrefilterExpandedItem, true);
                    }
                    PrefilterExpandedItems.Empty();
                }
                for (auto RootItem : *RootItems)
                {
                    TreeRootItems->Add(RootItem);
                }
            }
 
            TreeView->RequestTreeRefresh();
            bWasEnabled = bIsEnabled;
        }
    }
 
    void OnGetFilteredChildren(ItemType Parent, TArray<ItemType>& FilteredChildren)
    {
        if (bIsEnabled)
        {
            TArray<ItemType> AllChildren;
            GetChildrenDelegate.Execute(Parent, AllChildren);
            for (auto Child : AllChildren)
            {
                if (ItemsPassingFilter.Contains(Child))
                {
                    FilteredChildren.Add(Child);
                }
            }
        }
        else
        {
            GetChildrenDelegate.Execute(Parent, FilteredChildren);
        }
    }
 
private:
    bool ExpandAndCacheMatches(ItemType Parent)
    {
        bool bChildMatches = false;
        TArray<ItemType> AllChildren;
        GetChildrenDelegate.Execute(Parent, AllChildren);
        for (auto Child : AllChildren)
        {
            bChildMatches |= ExpandAndCacheMatches(Child);
        }
 
        bool bParentMatches = Filter->PassesFilter(Parent);
 
        if (bChildMatches || bParentMatches)
        {
            TreeView->SetItemExpansion(Parent, true);
            ItemsPassingFilter.Add(Parent);
            return true;
        }
 
        return false;
    }
 
private:
    STreeView<ItemType>* TreeView;
 
    IFilter<ItemType>* Filter;
 
    TArray<ItemType>* RootItems;
 
    TArray<ItemType>* TreeRootItems;
 
    FOnGetChildren GetChildrenDelegate;
 
    TSet<ItemType> ItemsPassingFilter;
 
    TSet<ItemType> PrefilterExpandedItems;
 
    bool bIsEnabled;
 
    bool bWasEnabled;
};