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, 50 insertions, 4 deletions

diff --git a/src/plugins/Ui/skinned/listwidget.cpp b/src/plugins/Ui/skinned/listwidget.cpp
index b82ab6e14..2a469e12d 100644
--- a/src/plugins/Ui/skinned/listwidget.cpp
+++ b/src/plugins/Ui/skinned/listwidget.cpp
@@ -64,6 +64,8 @@ ListWidget::ListWidget(QWidget *parent)
     m_pressed_index = INVALID_INDEX;
     m_first = 0;
     m_row_count = 0;
+    m_count = 0;
+    m_firstItem = 0;
     m_select_on_release = false;
 
     setAcceptDrops(true);
@@ -321,9 +323,19 @@ void ListWidget::updateList(int flags)
             m_first = qMax(0, m_model->count() - m_row_count);
             emit positionChanged(m_first, m_first);
         }
+        else if((m_count > 0) && (m_count != m_model->count()) &&
+                m_firstItem && m_model->item(m_first) != m_firstItem)
+        {
+            restoreFirstVisible();
+            emit positionChanged(m_first, m_model->count() - m_row_count);
+        }
         else
+        {
             emit positionChanged(m_first, m_model->count() - m_row_count);
+        }
 
+        m_firstItem = m_model->isEmpty() ? 0 : m_model->item(m_first);
+        m_count = m_model->count();
         items = m_model->mid(m_first, m_row_count);
 
         while(m_rows.count() < qMin(m_row_count, items.count()))
@@ -446,6 +458,8 @@ 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())
     {
@@ -564,6 +578,37 @@ 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::mouseMoveEvent(QMouseEvent *e)
 {
     if(e->buttons() == Qt::LeftButton)
diff --git a/src/plugins/Ui/skinned/listwidget.h b/src/plugins/Ui/skinned/listwidget.h
index 9e019d630..abaa5fec8 100644
--- a/src/plugins/Ui/skinned/listwidget.h
+++ b/src/plugins/Ui/skinned/listwidget.h
@@ -1,5 +1,5 @@
 /***************************************************************************
- *   Copyright (C) 2006-2017 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  *
@@ -109,18 +109,19 @@ private:
      * Returns string with queue number or(and) repeate flag for the item number \b i.
      */
     const QString getExtraString(int i);
-
     bool updateRowCount();
+    void restoreFirstVisible();
 
     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
     Skin *m_skin;
     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;