Editor: use combo box when creating pathgrids

Instead of using QLineEdit for user input, use a QComboBox populated
with valid choices. This prevents user from being able to create a
pathgrid for a non-existent cell.

apps/opencs/view/world/pathgridcreator.cpp

@@ -1,28 +1,74 @@
 #include "pathgridcreator.hpp"
 
+#include <QComboBox>
+#include <QLabel>
+#include <QSortFilterProxyModel>
+#include <QStringListModel>
+
 #include "../../model/world/data.hpp"
 
+std::string CSVWorld::PathgridCreator::getId() const
+{
+    return mCell->currentText().toUtf8().constData();
+}
+
 CSVWorld::PathgridCreator::PathgridCreator(
     CSMWorld::Data& data,
     QUndoStack& undoStack,
     const CSMWorld::UniversalId& id,
     bool relaxedIdRules
 ) : GenericCreator(data, undoStack, id, relaxedIdRules)
-{}
+{
+    setManualEditing(false);
+
+    QLabel *label = new QLabel("Cell ID", this);
+    insertBeforeButtons(label, false);
+
+    // Create combo box with case-insensitive sorting.
+    mCell = new QComboBox(this);
+    QSortFilterProxyModel *proxyModel = new QSortFilterProxyModel;
+    QStringListModel *listModel = new QStringListModel;
+    proxyModel->setSourceModel(listModel);
+    proxyModel->setSortCaseSensitivity(Qt::CaseInsensitive);
+    mCell->setModel(proxyModel);
+    insertBeforeButtons(mCell, true);
+
+    // Populate combo box with cells that don't have a pathgrid yet.
+    const CSMWorld::IdCollection<CSMWorld::Pathgrid>& pathgrids = getData().getPathgrids();
+    const CSMWorld::IdCollection<CSMWorld::Cell>& cells = getData().getCells();
+    const int cellCount = cells.getSize();
+    for (int i = 0; i < cellCount; ++i)
+    {
+        std::string cellId = cells.getId(i);
+        if (pathgrids.searchId(cellId) == -1)
+        {
+            mCell->addItem(QString::fromStdString(cellId));
+        }
+    }
+
+    mCell->model()->sort(0);
+    mCell->setCurrentIndex(0);
+}
 
 std::string CSVWorld::PathgridCreator::getErrors() const
 {
-    std::string pathgridId = getId();
+    std::string cellId = getId();
 
     // Check user input for any errors.
+    // The last two checks, cell with existing pathgrid and non-existent cell,
+    // shouldn't be needed but we absolutely want to make sure they never happen.
     std::string errors;
-    if (pathgridId.empty())
+    if (cellId.empty())
     {
-        errors = "No Pathgrid ID entered";
+        errors = "No cell ID selected";
     }
-    else if (getData().getPathgrids().searchId(pathgridId) > -1)
+    else if (getData().getPathgrids().searchId(cellId) > -1)
     {
-        errors = "Pathgrid with this ID already exists";
+        errors = "Pathgrid for selected cell ID already exists";
+    }
+    else if (getData().getCells().searchId(cellId) == -1)
+    {
+        errors = "Cell with selected cell ID does not exist";
     }
 
     return errors;

apps/opencs/view/world/pathgridcreator.hpp

@@ -1,6 +1,8 @@
 #ifndef PATHGRIDCREATOR_HPP
 #define PATHGRIDCREATOR_HPP
 
+class QComboBox;
+
 #include "genericcreator.hpp"
 
 namespace CSVWorld
@@ -10,6 +12,13 @@ namespace CSVWorld
     {
         Q_OBJECT
 
+        QComboBox *mCell;
+
+        private:
+
+            /// \return Cell ID selected by user.
+            virtual std::string getId() const;
+
         public:
 
             PathgridCreator(