When selecting a different item, but the item is the same

type of item, just update the existing panel to show the new
item's properties

This means that flicking between selecting items of the same
type will not create a new properties widget, so scroll
bar positions, focused widgets, etc are all maintained.

Makes using layouts less annoying.

python/gui/layout/qgslayoutitemwidget.sip

@@ -81,6 +81,17 @@ class QgsLayoutItemBaseWidget: QgsPanelWidget
  :rtype: QgsLayoutObject
 %End
 
+    bool setItem( QgsLayoutItem *item );
+%Docstring
+ Sets the current ``item`` to show in the widget. If true is returned, ``item``
+ was an acceptable type for display in this widget and the widget has been
+ updated to match ``item``'s properties.
+
+ If false is returned, then the widget could not be successfully updated
+ to show the properties of ``item``.
+ :rtype: bool
+%End
+
   protected:
 
     void registerDataDefinedButton( QgsPropertyOverrideButton *button, QgsLayoutObject::DataDefinedProperty property );
@@ -100,6 +111,19 @@ class QgsLayoutItemBaseWidget: QgsPanelWidget
  :rtype: QgsVectorLayer
 %End
 
+    virtual bool setNewItem( QgsLayoutItem *item );
+%Docstring
+ Attempts to update the widget to show the properties
+ for the specified ``item``.
+
+ Subclasses can override this if they support changing items in place.
+
+ Implementations must return true if the item was accepted and
+ the widget was updated.
+ :rtype: bool
+%End
+
+
 
 };
 
@@ -127,6 +151,8 @@ class QgsLayoutItemPropertiesWidget: QWidget
 
     void showFrameGroup( bool showGroup );
 
+    void setItem( QgsLayoutItem *item );
+
   protected slots:
     void initializeDataDefinedButtons();
 %Docstring

src/app/layout/qgslayoutdesignerdialog.cpp

@@ -630,6 +630,17 @@ void QgsLayoutDesignerDialog::showItemOptions( QgsLayoutItem *item, bool bringPa
 
       return;
     }
+    else
+    {
+      // try to reuse
+      if ( widget->setItem( item ) )
+      {
+        if ( bringPanelToFront )
+          mItemDock->setUserVisible( true );
+
+        return;
+      }
+    }
   }
 
   std::unique_ptr< QgsLayoutItemBaseWidget > widget( QgsGui::layoutItemGuiRegistry()->createItemWidget( item ) );

src/app/layout/qgslayoutmapwidget.cpp

@@ -68,8 +68,8 @@ QgsLayoutMapWidget::QgsLayoutMapWidget( QgsLayoutItemMap *item )
   mMapRotationSpinBox->setClearValue( 0 );
 
   //add widget for general composer item properties
-  QgsLayoutItemPropertiesWidget *itemPropertiesWidget = new QgsLayoutItemPropertiesWidget( this, item );
-  mainLayout->addWidget( itemPropertiesWidget );
+  mItemPropertiesWidget = new QgsLayoutItemPropertiesWidget( this, item );
+  mainLayout->addWidget( mItemPropertiesWidget );
 
   mScaleLineEdit->setValidator( new QDoubleValidator( mScaleLineEdit ) );
 
@@ -141,6 +141,17 @@ QgsLayoutMapWidget::QgsLayoutMapWidget( QgsLayoutItemMap *item )
   blockAllSignals( false );
 }
 
+bool QgsLayoutMapWidget::setNewItem( QgsLayoutItem *item )
+{
+  if ( item->type() != QgsLayoutItemRegistry::LayoutMap )
+    return false;
+
+  mMapItem = qobject_cast< QgsLayoutItemMap * >( item );
+  mItemPropertiesWidget->setItem( mMapItem );
+
+  return true;
+}
+
 void QgsLayoutMapWidget::populateDataDefinedButtons()
 {
   updateDataDefinedButton( mScaleDDBtn );

src/app/layout/qgslayoutmapwidget.h

@@ -89,6 +89,7 @@ class QgsLayoutMapWidget: public QgsLayoutItemBaseWidget, private Ui::QgsLayoutM
     void blockOverviewItemsSignals( bool block );
 
   protected:
+    bool setNewItem( QgsLayoutItem *item ) override;
 
     void addPageToToolbox( QWidget *widget, const QString &name );
 
@@ -124,6 +125,7 @@ class QgsLayoutMapWidget: public QgsLayoutItemBaseWidget, private Ui::QgsLayoutM
 
   private:
     QgsLayoutItemMap *mMapItem = nullptr;
+    QgsLayoutItemPropertiesWidget *mItemPropertiesWidget = nullptr;
 
     //! Sets extent of composer map from line edits
     void updateComposerExtentFromGui();

src/gui/layout/qgslayoutitemwidget.cpp

@@ -139,6 +139,17 @@ QgsLayoutObject *QgsLayoutItemBaseWidget::layoutObject()
   return mObject;
 }
 
+bool QgsLayoutItemBaseWidget::setItem( QgsLayoutItem *item )
+{
+  if ( setNewItem( item ) )
+  {
+    mObject = item;
+    return true;
+  }
+
+  return false;
+}
+
 void QgsLayoutItemBaseWidget::registerDataDefinedButton( QgsPropertyOverrideButton *button, QgsLayoutObject::DataDefinedProperty property )
 {
   mConfigObject->initializeDataDefinedButton( button, property );
@@ -154,6 +165,11 @@ QgsVectorLayer *QgsLayoutItemBaseWidget::coverageLayer() const
   return mConfigObject->coverageLayer();
 }
 
+bool QgsLayoutItemBaseWidget::setNewItem( QgsLayoutItem * )
+{
+  return false;
+}
+
 #if 0 //TODO
 QgsAtlasComposition *QgsLayoutItemBaseWidget::atlasComposition() const
 {
@@ -178,7 +194,6 @@ void QgsLayoutItemPropertiesWidget::updateVariables()
 
 QgsLayoutItemPropertiesWidget::QgsLayoutItemPropertiesWidget( QWidget *parent, QgsLayoutItem *item )
   : QWidget( parent )
-  , mItem( item )
   , mConfigObject( new QgsLayoutConfigObject( this, item ) )
   , mFreezeXPosSpin( false )
   , mFreezeYPosSpin( false )
@@ -186,20 +201,19 @@ QgsLayoutItemPropertiesWidget::QgsLayoutItemPropertiesWidget( QWidget *parent, Q
   , mFreezeHeightSpin( false )
   , mFreezePageSpin( false )
 {
-
   setupUi( this );
 
   mItemRotationSpinBox->setClearValue( 0 );
   mStrokeUnitsComboBox->linkToWidget( mStrokeWidthSpinBox );
-  mStrokeUnitsComboBox->setConverter( &mItem->layout()->context().measurementConverter() );
+  mStrokeUnitsComboBox->setConverter( &item->layout()->context().measurementConverter() );
 
   mPosUnitsComboBox->linkToWidget( mXPosSpin );
   mPosUnitsComboBox->linkToWidget( mYPosSpin );
   mSizeUnitsComboBox->linkToWidget( mWidthSpin );
   mSizeUnitsComboBox->linkToWidget( mHeightSpin );
 
-  mPosUnitsComboBox->setConverter( &mItem->layout()->context().measurementConverter() );
-  mSizeUnitsComboBox->setConverter( &mItem->layout()->context().measurementConverter() );
+  mPosUnitsComboBox->setConverter( &item->layout()->context().measurementConverter() );
+  mSizeUnitsComboBox->setConverter( &item->layout()->context().measurementConverter() );
 
   mPosLockAspectRatio->setWidthSpinBox( mXPosSpin );
   mPosLockAspectRatio->setHeightSpinBox( mYPosSpin );
@@ -249,14 +263,11 @@ QgsLayoutItemPropertiesWidget::QgsLayoutItemPropertiesWidget( QWidget *parent, Q
 
   initializeDataDefinedButtons();
 
-  setValuesForGuiElements();
-
 #if 0 //TODO
   connect( mItem->composition(), &QgsComposition::paperSizeChanged, this, &QgsLayoutItemPropertiesWidget::setValuesForGuiPositionElements );
 #endif
 
-  connect( mItem, &QgsLayoutItem::sizePositionChanged, this, &QgsLayoutItemPropertiesWidget::setValuesForGuiPositionElements );
-  connect( mItem, &QgsLayoutObject::changed, this, &QgsLayoutItemPropertiesWidget::setValuesForGuiNonPositionElements );
+  setItem( item );
 
   connect( mOpacityWidget, &QgsOpacityWidget::opacityChanged, this, &QgsLayoutItemPropertiesWidget::opacityChanged );
 
@@ -264,10 +275,10 @@ QgsLayoutItemPropertiesWidget::QgsLayoutItemPropertiesWidget( QWidget *parent, Q
   connect( mVariableEditor, &QgsVariableEditorWidget::scopeChanged, this, &QgsLayoutItemPropertiesWidget::variablesChanged );
   // listen out for variable edits
   connect( QgsApplication::instance(), &QgsApplication::customVariablesChanged, this, &QgsLayoutItemPropertiesWidget::updateVariables );
-  connect( mItem->layout()->project(), &QgsProject::customVariablesChanged, this, &QgsLayoutItemPropertiesWidget::updateVariables );
+  connect( item->layout()->project(), &QgsProject::customVariablesChanged, this, &QgsLayoutItemPropertiesWidget::updateVariables );
 
-  if ( mItem->layout() )
-    connect( mItem->layout(), &QgsLayout::variablesChanged, this, &QgsLayoutItemPropertiesWidget::updateVariables );
+  if ( item->layout() )
+    connect( item->layout(), &QgsLayout::variablesChanged, this, &QgsLayoutItemPropertiesWidget::updateVariables );
 }
 
 void QgsLayoutItemPropertiesWidget::showBackgroundGroup( bool showGroup )
@@ -280,6 +291,20 @@ void QgsLayoutItemPropertiesWidget::showFrameGroup( bool showGroup )
   mFrameGroupBox->setVisible( showGroup );
 }
 
+void QgsLayoutItemPropertiesWidget::setItem( QgsLayoutItem *item )
+{
+  if ( mItem )
+  {
+    disconnect( mItem, &QgsLayoutItem::sizePositionChanged, this, &QgsLayoutItemPropertiesWidget::setValuesForGuiPositionElements );
+    disconnect( mItem, &QgsLayoutObject::changed, this, &QgsLayoutItemPropertiesWidget::setValuesForGuiNonPositionElements );
+  }
+  mItem = item;
+  connect( mItem, &QgsLayoutItem::sizePositionChanged, this, &QgsLayoutItemPropertiesWidget::setValuesForGuiPositionElements );
+  connect( mItem, &QgsLayoutObject::changed, this, &QgsLayoutItemPropertiesWidget::setValuesForGuiNonPositionElements );
+
+  setValuesForGuiElements();
+}
+
 //slots
 
 void QgsLayoutItemPropertiesWidget::mFrameColorButton_colorChanged( const QColor &newFrameColor )

src/gui/layout/qgslayoutitemwidget.h

@@ -126,6 +126,16 @@ class GUI_EXPORT QgsLayoutItemBaseWidget: public QgsPanelWidget
      */
     QgsLayoutObject *layoutObject();
 
+    /**
+     * Sets the current \a item to show in the widget. If true is returned, \a item
+     * was an acceptable type for display in this widget and the widget has been
+     * updated to match \a item's properties.
+     *
+     * If false is returned, then the widget could not be successfully updated
+     * to show the properties of \a item.
+     */
+    bool setItem( QgsLayoutItem *item );
+
   protected:
 
     /**
@@ -144,6 +154,18 @@ class GUI_EXPORT QgsLayoutItemBaseWidget: public QgsPanelWidget
      */
     QgsVectorLayer *coverageLayer() const;
 
+    /**
+     * Attempts to update the widget to show the properties
+     * for the specified \a item.
+     *
+     * Subclasses can override this if they support changing items in place.
+     *
+     * Implementations must return true if the item was accepted and
+     * the widget was updated.
+     */
+    virtual bool setNewItem( QgsLayoutItem *item );
+
+
 #if 0 //TODO
     //! Returns the atlas for the composition
     QgsAtlasComposition *atlasComposition() const;
@@ -176,6 +198,8 @@ class GUI_EXPORT QgsLayoutItemPropertiesWidget: public QWidget, private Ui::QgsL
 
     void showFrameGroup( bool showGroup );
 
+    void setItem( QgsLayoutItem *item );
+
   protected slots:
     //! Initializes data defined buttons to current atlas coverage layer
     void initializeDataDefinedButtons();