Qt example (#296)

CMakeLists.txt

@@ -26,7 +26,7 @@ include(cmake/prelude.cmake)
 
 project(
     ReactivePlusPlus
-    VERSION 0.1.4
+    VERSION 0.2.0
     DESCRIPTION "ReactivePlusPlus is library for building asynchronous event-driven streams of data with help of sequences of primitive operators in the declarative form"
     HOMEPAGE_URL "https://github.com/victimsnino/ReactivePlusPlus"
     LANGUAGES CXX

src/examples/rppqt/CMakeLists.txt

@@ -1,2 +1,3 @@
 add_subdirectory(interactive_window)
 add_subdirectory(doxygen)
+add_subdirectory(multi_threaded)

src/examples/rppqt/multi_threaded/CMakeLists.txt

@@ -0,0 +1,9 @@
+SET(TARGET multi_threaded)
+add_executable(${TARGET}
+    ${TARGET}.cpp
+)
+
+target_link_libraries(${TARGET} PRIVATE rppqt ${RPP_QT_TARGET}::Widgets)
+set_target_properties(${TARGET} PROPERTIES FOLDER Examples/rppqt)
+
+rpp_add_qt_support_to_executable(${TARGET})

src/examples/rppqt/multi_threaded/multi_threaded.cpp

@@ -0,0 +1,71 @@
+#include <rpp/rpp.hpp>
+#include <rppqt/rppqt.hpp>
+
+#include <iostream>
+
+#include <QApplication>
+#include <QLabel>
+#include <QPushButton>
+#include <QMainWindow>
+#include <QVBoxLayout>
+
+int main(int argc, char* argv[])
+{
+    QApplication app{argc, argv};
+    QVBoxLayout  vbox{};
+
+    QLabel      label{};
+    QPushButton button{"CLick me"};
+    vbox.addWidget(&label);
+    vbox.addWidget(&button);
+    QMainWindow window{};
+
+    window.setCentralWidget(new QWidget);
+    window.centralWidget()->setLayout(&vbox);
+
+    window.show();
+
+    rpp::source::interval(std::chrono::seconds{1})
+            .tap([](const auto&)
+            {
+                std::cout << "Interval from thread: " << std::this_thread::get_id() << std::endl;
+            })
+            .combine_latest([](size_t index, size_t amount_of_clicks)
+                            {
+                                return QString("Seconds since start: %1 Clicks since start: %2").arg(index).arg(amount_of_clicks);
+                            },
+                            rppqt::source::from_signal(button, &QPushButton::pressed).scan(size_t{},
+                                                                                           [](size_t seed, const auto&)
+                                                                                           {
+                                                                                               return seed + 1;
+                                                                                           })
+                                                                                     .tap([](const auto&)
+                                                                                     {
+                                                                                         std::cout << "Click from thread: " <<
+                                                                                                 std::this_thread::get_id() << std::endl;
+                                                                                     })
+                                                                                     .start_with(size_t{0}))
+            .subscribe_on(rpp::schedulers::new_thread{})
+            .observe_on(rppqt::schedulers::main_thread_scheduler{})
+            .subscribe([&](const QString& text)
+            {
+                std::cout << "Text updated from thread: " << std::this_thread::get_id() << std::endl;
+                label.setText(text);
+            });
+
+    std::cout << "Application thread: " << std::this_thread::get_id() << std::endl;
+
+    // There we have application's thread, "new_thread" where observable subscribed and interval events happened.
+    // But we need to update GUI's objects in main thread, so, we forces observable to emit items to subscribe in QT's main thread
+    // Example of output:
+    /*
+        Application thread: 19748       <----- main thread
+        Interval from thread: 30604     <----- interval happens from another thread
+        Text updated from thread: 19748 <----- but update then transfered to main thread
+        Click from thread: 19748        <----- click happens from main thread due to QT logic
+        Text updated from thread: 19748 <----- and update happens in main thread
+        Interval from thread: 30604
+        Text updated from thread: 19748
+     */
+    return app.exec();
+}

src/rppqt/rppqt/schedulers/main_thread_scheduler.hpp

@@ -56,7 +56,7 @@ class main_thread_scheduler final : public rpp::schedulers::details::scheduler_t
                 throw utils::no_active_qapplication{
                     "Pointer to application is null. Create QApplication before using main_thread_scheduler!"};
 
-            const auto duration = std::chrono::duration_cast<std::chrono::milliseconds>(now() - time_point).count();
+            const auto duration = std::max(std::chrono::milliseconds{0}, std::chrono::duration_cast<std::chrono::milliseconds>(time_point - now()));
             QTimer::singleShot(duration, application, std::move(fn));
         }