[attribute table] fix long UI freeze when resizing columns for large filtered datasets (#6341)

python/core/qgsattributetableconfig.sip.in

@@ -179,6 +179,12 @@ Get the sort order
 Set the sort order
 
 .. versionadded:: 2.16
+%End
+
+    bool hasSameColumns( const QgsAttributeTableConfig &other ) const;
+%Docstring
+Compare this configuration's columns name, type, and order to ``other``.
+The column's width is not considered.
 %End
 
     bool operator!= ( const QgsAttributeTableConfig &other ) const;

src/core/qgsattributetableconfig.cpp

@@ -283,6 +283,25 @@ void QgsAttributeTableConfig::writeXml( QDomNode &node ) const
   node.appendChild( configElement );
 }
 
+bool QgsAttributeTableConfig::hasSameColumns( const QgsAttributeTableConfig &other ) const
+{
+  if ( columns().size() == other.columns().size() )
+  {
+    for ( int i = 0; i < columns().size(); i++ )
+    {
+      if ( columns().at( i ).name != other.columns().at( i ).name ||
+           columns().at( i ).type != other.columns().at( i ).type ||
+           columns().at( i ).hidden != other.columns().at( i ).hidden )
+      {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  return false;
+}
+
 bool QgsAttributeTableConfig::ColumnConfig::operator== ( const ColumnConfig &other ) const
 {
   return type == other.type && name == other.name && hidden == other.hidden && width == other.width;

src/core/qgsattributetableconfig.h

@@ -190,6 +190,12 @@ class CORE_EXPORT QgsAttributeTableConfig
      */
     void setSortOrder( Qt::SortOrder sortOrder );
 
+    /**
+     * Compare this configuration's columns name, type, and order to \a other.
+     * The column's width is not considered.
+     */
+    bool hasSameColumns( const QgsAttributeTableConfig &other ) const;
+
     /**
      * Compare this configuration to other.
      */

src/gui/attributetable/qgsattributetablefiltermodel.cpp

@@ -131,11 +131,16 @@ int QgsAttributeTableFilterModel::columnCount( const QModelIndex &parent ) const
 
 void QgsAttributeTableFilterModel::setAttributeTableConfig( const QgsAttributeTableConfig &config )
 {
+  QgsAttributeTableConfig oldConfig = mConfig;
   mConfig = config;
   mConfig.update( layer()->fields() );
 
-  QVector<int> newColumnMapping;
+  if ( mConfig.hasSameColumns( oldConfig ) )
+  {
+    return;
+  }
 
+  QVector<int> newColumnMapping;
   Q_FOREACH ( const QgsAttributeTableConfig::ColumnConfig &columnConfig, mConfig.columns() )
   {
     // Hidden? Forget about this column

tests/src/python/test_qgsattributetableconfig.py

@@ -109,6 +109,39 @@ class TestQgsAttributeTableConfig(unittest.TestCase):
         self.assertFalse(config.columnHidden(0))
         self.assertTrue(config.columnHidden(1))
 
+    def testSameColumns(self):
+        """ test hasSameColumns() check """
+
+        config = QgsAttributeTableConfig()
+        c1 = QgsAttributeTableConfig.ColumnConfig()
+        c1.name = 'test'
+        c1.hidden = False
+        c1.width = 100
+        c2 = QgsAttributeTableConfig.ColumnConfig()
+        c2.name = 'test2'
+        c2.hidden = False
+        c2.width = 120
+        config.setColumns([c1, c2])
+        config2 = QgsAttributeTableConfig()
+
+        config2.setColumns([c1, c2])
+        self.assertTrue(config.hasSameColumns(config2))
+
+        c1.width = 200
+        config2.setColumns([c1, c2])
+        self.assertTrue(config.hasSameColumns(config2))
+
+        c1.hidden = True
+        config2.setColumns([c1, c2])
+        self.assertFalse(config.hasSameColumns(config2))
+
+        config2.setColumns([c2, c1])
+        self.assertFalse(config.hasSameColumns(config2))
+
+        c2.name = 'test3'
+        config2.setColumns([c1, c2])
+        self.assertFalse(config.hasSameColumns(config2))
+
     def testMapVisibleColumn(self):
         pass