Fix the update of TabView.currentIndex when inserting/removing tabs

- Update currentIndex when adding or inserting tabs.
- Make sure that we update the current index before updating the array
  to avoid a state of currentIndex > count -1 when removing the
  last tab, where a property binding on TabView.count could try
  fetching a tab past the array limit through TabView.getTab.
- Only decrease currentIndex when removedIndex <= currentIndex to
  keep the current tab active when possible. Activate the next tab
  instead of the previous one when the current tab is removed to make
  it more instinctive to remove multiple tabs successively.
- Keep the current behavior of leaving currentIndex to 0 when
  removing the last tab.

Change-Id: I030b86a03ce73f1177b1f04857abbdc2f7ec5835
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>

2 files changed, 52 insertions, 2 deletions

diff --git a/src/controls/TabView.qml b/src/controls/TabView.qml
index 5be224ce..440606e0 100644
--- a/src/controls/TabView.qml
+++ b/src/controls/TabView.qml
@@ -103,6 +103,7 @@ FocusScope {
         __tabs.insert(index, {tab: tab})
         tab.__inserted = true
         tab.parent = stack
+        __didInsertIndex(index)
         __setOpacities()
         return tab
     }
@@ -110,10 +111,9 @@ FocusScope {
     /*! Removes and destroys a tab at the given \a index. */
     function removeTab(index) {
         var tab = __tabs.get(index).tab
+        __willRemoveIndex(index)
         __tabs.remove(index, 1)
         tab.destroy()
-        if (currentIndex > 0)
-            currentIndex--
         __setOpacities()
     }
 
@@ -153,6 +153,19 @@ FocusScope {
     onCurrentIndexChanged: __setOpacities()
 
     /*! \internal */
+    function __willRemoveIndex(index) {
+        // Make sure currentIndex will points to the same tab after the removal.
+        // Also activate the next index if the current index is being removed,
+        // except when it's both the current and last index.
+        if (count > 1 && (currentIndex > index || currentIndex == count -1))
+            --currentIndex
+    }
+    function __didInsertIndex(index) {
+        // Make sure currentIndex points to the same tab as before the insertion.
+        if (count > 1 && currentIndex >= index)
+            currentIndex++
+    }
+
     function __setOpacities() {
         for (var i = 0; i < __tabs.count; ++i) {
             var child = __tabs.get(i).tab
@@ -229,6 +242,7 @@ FocusScope {
                         if (completed)
                             tab.Component.onDestruction.connect(stack.onDynamicTabDestroyed.bind(tab))
                         __tabs.append({tab: tab})
+                        __didInsertIndex(__tabs.count - 1)
                         tabAdded = true
                     }
                 }
@@ -239,6 +253,7 @@ FocusScope {
             function onDynamicTabDestroyed() {
                 for (var i = 0; i < __tabs.count; ++i) {
                     if (__tabs.get(i).tab === this) {
+                        __willRemoveIndex(i)
                         __tabs.remove(i, 1)
                         __setOpacities()
                         break
diff --git a/tests/auto/controls/data/tst_tabview.qml b/tests/auto/controls/data/tst_tabview.qml
index b7de67ba..9e556dd1 100644
--- a/tests/auto/controls/data/tst_tabview.qml
+++ b/tests/auto/controls/data/tst_tabview.qml
@@ -84,22 +84,53 @@ TestCase {
 
     function test_addRemoveTab() {
         var tabView = Qt.createQmlObject('import QtQuick 2.2; import QtQuick.Controls 1.2; TabView { }', testCase, '');
+
+        function verifyCurrentIndexCountDiff() {
+            verify(!tabView.currentIndex || tabView.count > tabView.currentIndex)
+        }
+        tabView.currentIndexChanged.connect(verifyCurrentIndexCountDiff)
+        tabView.countChanged.connect(verifyCurrentIndexCountDiff)
+
         compare(tabView.count, 0)
+        compare(tabView.currentIndex, 0)
         tabView.addTab("title 1", newTab)
         compare(tabView.count, 1)
+        compare(tabView.currentIndex, 0)
         tabView.addTab("title 2", newTab)
         compare(tabView.count, 2)
+        compare(tabView.currentIndex, 0)
         compare(tabView.getTab(0).title, "title 1")
         compare(tabView.getTab(1).title, "title 2")
 
+        tabView.currentIndex = 1
+
         tabView.insertTab(1, "title 3")
         compare(tabView.count, 3)
+        compare(tabView.currentIndex, 2)
         compare(tabView.getTab(0).title, "title 1")
         compare(tabView.getTab(1).title, "title 3")
         compare(tabView.getTab(2).title, "title 2")
 
         tabView.insertTab(0, "title 4")
         compare(tabView.count, 4)
+        compare(tabView.currentIndex, 3)
+        compare(tabView.getTab(0).title, "title 4")
+        compare(tabView.getTab(1).title, "title 1")
+        compare(tabView.getTab(2).title, "title 3")
+        compare(tabView.getTab(3).title, "title 2")
+
+        tabView.insertTab(tabView.count, "title 5")
+        compare(tabView.count, 5)
+        compare(tabView.currentIndex, 3)
+        compare(tabView.getTab(0).title, "title 4")
+        compare(tabView.getTab(1).title, "title 1")
+        compare(tabView.getTab(2).title, "title 3")
+        compare(tabView.getTab(3).title, "title 2")
+        compare(tabView.getTab(4).title, "title 5")
+
+        tabView.removeTab(tabView.count - 1)
+        compare(tabView.count, 4)
+        compare(tabView.currentIndex, 3)
         compare(tabView.getTab(0).title, "title 4")
         compare(tabView.getTab(1).title, "title 1")
         compare(tabView.getTab(2).title, "title 3")
@@ -107,21 +138,25 @@ TestCase {
 
         tabView.removeTab(0)
         compare(tabView.count, 3)
+        compare(tabView.currentIndex, 2)
         compare(tabView.getTab(0).title, "title 1")
         compare(tabView.getTab(1).title, "title 3")
         compare(tabView.getTab(2).title, "title 2")
 
         tabView.removeTab(1)
         compare(tabView.count, 2)
+        compare(tabView.currentIndex, 1)
         compare(tabView.getTab(0).title, "title 1")
         compare(tabView.getTab(1).title, "title 2")
 
         tabView.removeTab(1)
         compare(tabView.count, 1)
+        compare(tabView.currentIndex, 0)
         compare(tabView.getTab(0).title, "title 1")
 
         tabView.removeTab(0)
         compare(tabView.count, 0)
+        compare(tabView.currentIndex, 0)
         tabView.destroy()
     }