[cpp] Add Qt Desginer widget plugin examples

cpp/qt/designer-plugin-collection/treeview.h

@@ -0,0 +1,36 @@
+/*##############################################################################
+## Author: Shaun Reed                                                         ##
+## Legal: All Content (c) 2022 Shaun Reed, all rights reserved                ##
+## About: Tree viewer                                                         ##
+##                                                                            ##
+## Contact: shaunrd0@gmail.com  | URL: www.shaunreed.com | GitHub: shaunrd0   ##
+################################################################################
+*/
+
+#ifndef KLIPS_TREEVIEW_H
+#define KLIPS_TREEVIEW_H
+
+#include "widget-plugin-library_export.h"
+#include <app-dir.h>
+
+#include <QFileSystemModel>
+#include <QSortFilterProxyModel>
+#include <QTreeView>
+
+class WIDGET_PLUGIN_LIBRARY_EXPORT TreeView : public QTreeView {
+  Q_OBJECT
+
+public:
+  explicit TreeView(QWidget *parent = nullptr) : QTreeView(parent) {
+    QFileSystemModel *model = new QFileSystemModel;
+    QSortFilterProxyModel *proxy = new QSortFilterProxyModel(this);
+    QModelIndex rootModelIndex = model->setRootPath(APP_DIR);
+    proxy->setSourceModel(model);
+    setModel(proxy);
+    setRootIndex(proxy->mapFromSource(rootModelIndex));
+  }
+
+  ~TreeView() = default;
+};
+
+#endif // KLIPS_TREEVIEW_H