do not lose first visible item after adding more tracks

git-svn-id: http://svn.code.sf.net/p/qmmp-dev/code/trunk/qmmp@8399 90c681e8-e032-0410-971d-27865f9a5e38

2 files changed, 53 insertions, 4 deletions

diff --git a/src/plugins/Ui/qsui/listwidget.cpp b/src/plugins/Ui/qsui/listwidget.cpp
index 58b3754a0..524563fb1 100644
--- a/src/plugins/Ui/qsui/listwidget.cpp
+++ b/src/plugins/Ui/qsui/listwidget.cpp
@@ -66,6 +66,8 @@ ListWidget::ListWidget(PlayListModel *model, QWidget *parent)
     m_first = 0;
     m_row_count = 0;
     m_select_on_release = false;
+    m_count = 0;
+    m_firstItem = 0;
 
     setAcceptDrops(true);
     setMouseTracking(true);
@@ -177,6 +179,8 @@ void ListWidget::setModel(PlayListModel *selected, PlayListModel *previous)
     }
     qApp->processEvents();
     m_model = selected;
+    m_count = m_model->count();
+    m_firstItem = 0;
 
     if(m_model->property("first_visible").isValid())
     {
@@ -407,6 +411,14 @@ void ListWidget::updateList(int flags)
             m_scrollBar->setValue(m_first);
             emit positionChanged(m_first, m_first);
         }
+        else if(!m_filterMode && (m_count > 0) && (m_count != m_model->count()) &&
+                m_firstItem && m_model->item(m_first) != m_firstItem)
+        {
+            restoreFirstVisible();
+            m_scrollBar->setMaximum(count - m_row_count);
+            m_scrollBar->setValue(m_first);
+            emit positionChanged(m_first, m_model->count() - m_row_count);
+        }
         else
         {
             m_scrollBar->setMaximum(count - m_row_count);
@@ -415,6 +427,11 @@ void ListWidget::updateList(int flags)
         }
         m_scrollBar->blockSignals(false);
 
+        if(!m_filterMode)
+        {
+            m_firstItem = m_model->isEmpty() ? 0 : m_model->item(m_first);
+            m_count = m_model->count();
+        }
         items = m_filterMode ? m_filteredItems.mid(m_first, m_row_count) : m_model->mid(m_first, m_row_count);
 
         while(m_rows.count() < qMin(m_row_count, items.count()))
@@ -654,6 +671,37 @@ bool ListWidget::updateRowCount()
     return false;
 }
 
+void ListWidget::restoreFirstVisible()
+{
+    if(m_first >= m_model->count() || m_firstItem == m_model->item(m_first))
+        return;
+
+    int delta = m_model->count() - m_count;
+
+    if(delta > 0)
+    {
+        for(int i = m_first + 1; i <= qMin(m_model->count() - 1, m_first + delta); ++i)
+        {
+            if(m_model->item(i) == m_firstItem)
+            {
+                m_first = i;
+                break;
+            }
+        }
+    }
+    else
+    {
+        for(int i = m_first - 1; i >= qMax(0, m_first + delta); --i)
+        {
+            if(m_model->item(i) == m_firstItem)
+            {
+                m_first = i;
+                break;
+            }
+        }
+    }
+}
+
 void ListWidget::updateScrollBars()
 {
     bool rtl = layoutDirection() == Qt::RightToLeft;
diff --git a/src/plugins/Ui/qsui/listwidget.h b/src/plugins/Ui/qsui/listwidget.h
index 284401c81..ab981f4d5 100644
--- a/src/plugins/Ui/qsui/listwidget.h
+++ b/src/plugins/Ui/qsui/listwidget.h
@@ -1,5 +1,5 @@
 /***************************************************************************
- *   Copyright (C) 2006-2016 by Ilya Kotov                                 *
+ *   Copyright (C) 2006-2018 by Ilya Kotov                                 *
  *   forkotov02@ya.ru                                                      *
  *                                                                         *
  *   This program is free software; you can redistribute it and/or modify  *
@@ -113,18 +113,19 @@ private:
      * Returns string with queue number or(and) repeate flag for the \b item.
      */
     const QString getExtraString(PlayListItem *item);
-
     bool updateRowCount();
+    void restoreFirstVisible();
     void updateScrollBars();
 
     bool m_update;
     int m_pressed_index;
     QMenu *m_menu;
     PlayListModel *m_model;
-    int m_row_count, m_first;
+    int m_row_count, m_first, m_count; //visible rows, first visible index, total item count
+    PlayListItem *m_firstItem; //first visible item
     int m_anchor_index;
     /*!
-     * Scroll direction that is preforming in current moment.
+     * Scroll direction that is performing in current moment.
      */
     ScrollDirection m_scroll_direction;
     int m_prev_y;