examples/ui/infinite_lazy_list/src/main.cpp

Note

This Source File belongs to Infinite Lazy List Example. Please follow the link for example explanation.

/*
 * AUI Framework - Declarative UI toolkit for modern C++20
 * Copyright (C) 2020-2025 Alex2772 and Contributors
 *
 * SPDX-License-Identifier: MPL-2.0
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
 
#include <range/v3/all.hpp>
 
#include <AUI/Platform/Entry.h>
#include "AUI/Platform/AWindow.h"
#include "AUI/Util/UIBuildingHelpers.h"
#include "AUI/View/AScrollArea.h"
#include "AUI/View/ASpinnerV2.h"
#include "AUI/View/AForEachUI.h"
#include "AUI/Model/AListModel.h"
#include "AUI/Thread/AAsyncHolder.h"
 
using namespace declarative;
using namespace ass;
using namespace std::chrono_literals;
 
struct Item {
   AProperty<AString> value;
};
 
struct State {
   AProperty<AVector<_<Item>>> items;
   AProperty<bool> needMore = false;
   AAsyncHolder asyncTasks;
};
 
_<AView> myLazyList(_<State> state) {
   // note that we observe for transition to true here, not the current state of property
   // see PropertyTest_Observing_changes for more info
   AObject::connect(state->needMore.changed, AObject::GENERIC_OBSERVER, [state](bool newState){
       if (!newState) { // we're interested in transitions to true state only.
           return;
       }
       auto loadFrom = state->items->size(); // base index to load from.
       state->asyncTasks << async {
           // perform "loading" task on a worker thread.
 
           AThread::sleep(500ms); // imitate hard work here
 
           // aka "loaded" from backend storage of some kind
           auto loadedItems = AVector<_<Item>>::generate(20, [&](size_t i) {
               return aui::ptr::manage(new Item { .value = "Item {}"_format(loadFrom + i) });
           });
 
           ui_thread { // back to main thread.
               state->items.writeScope()->insertAll(loadedItems);
               state->needMore = false;
           };
       };
   });
 
   return Vertical {
       AUI_DECLARATIVE_FOR(i, *state->items, AVerticalLayout) { return Label{} & i->value; },
       Centered {
         _new<ASpinnerV2>() let {
                 AObject::connect(it->redrawn, AObject::GENERIC_OBSERVER, [state] {
                     // when a spinner appears, we indicate that we need more items.
                     state->needMore = true;
                 });
             },
       },
   };
}
 
AUI_ENTRY {
   auto window = _new<AWindow>("Infinite Lazy List", 200_dp, 300_dp);
   window->setContents(Stacked { AScrollArea::Builder().withContents(myLazyList(_new<State>())) });
   window->show();
 
   return 0;
}

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