[browser] Restore attribute preview from 2.x standalone browser

This resurrects an "attributes" tab in the browser layer properties
panel/window, showing a preview of the attributes for a vector
layer.

For performance, we limit the table to show a maximum of the first
100 rows. (There's no way to "page" attribute table requests
currently or load them in the background). But besides, the table
is really only good for a quick preview and in this case it's ok
to only show a subset of records.

Author: nyalldawson

src/gui/qgsbrowserdockwidget_p.cpp

@@ -41,6 +41,9 @@
 #include "qgsgui.h"
 #include "qgsnative.h"
 #include "qgsmaptoolpan.h"
+#include "qgsvectorlayercache.h"
+#include "qgsattributetablemodel.h"
+#include "qgsattributetablefiltermodel.h"
 #include <QDesktopServices>
 
 #include <QDragEnterEvent>
@@ -133,6 +136,11 @@ QgsBrowserLayerProperties::QgsBrowserLayerProperties( QWidget *parent )
       mMapCanvas->freeze( false );
       mMapCanvas->refresh();
     }
+    else if ( mTabWidget->currentWidget() == mAttributesTab )
+    {
+      if ( ! mAttributeTableFilterModel )
+        loadAttributeTable();
+    }
   } );
 }
 
@@ -202,6 +210,13 @@ void QgsBrowserLayerProperties::setItem( QgsDataItem *item )
     return;
   }
 
+  mAttributeTable->setModel( nullptr );
+  if ( mAttributeTableFilterModel )
+  {
+    // Cleanup
+    mAttributeTableFilterModel->deleteLater();
+    mAttributeTableFilterModel = nullptr;
+  }
   if ( mLayer && mLayer->isValid() )
   {
     bool ok = false;
@@ -212,6 +227,12 @@ void QgsBrowserLayerProperties::setItem( QgsDataItem *item )
     mMapCanvas->setDestinationCrs( mLayer->crs() );
     mMapCanvas->setLayers( QList< QgsMapLayer * >() << mLayer.get() );
     mMapCanvas->zoomToFullExtent();
+
+    if ( mAttributesTab && mLayer->type() != QgsMapLayer::VectorLayer )
+    {
+      mTabWidget->removeTab( mTabWidget->indexOf( mAttributesTab ) );
+      mAttributesTab = nullptr;
+    }
   }
 
   QString myStyle = QgsApplication::reportStyleSheet();
@@ -247,6 +268,39 @@ void QgsBrowserLayerProperties::urlClicked( const QUrl &url )
     QDesktopServices::openUrl( url );
 }
 
+void QgsBrowserLayerProperties::loadAttributeTable()
+{
+  if ( !mLayer || !mLayer->isValid() || mLayer->type() != QgsMapLayer::VectorLayer )
+    return;
+
+  // Initialize the cache
+  QgsVectorLayerCache *layerCache = new QgsVectorLayerCache( qobject_cast< QgsVectorLayer * >( mLayer.get() ), 1000, this );
+  layerCache->setCacheGeometry( false );
+  QgsAttributeTableModel *tableModel = new QgsAttributeTableModel( layerCache, this );
+  mAttributeTableFilterModel = new QgsAttributeTableFilterModel( nullptr, tableModel, this );
+  tableModel->setRequest( QgsFeatureRequest().setFlags( QgsFeatureRequest::NoGeometry ).setLimit( 100 ) );
+  layerCache->setParent( tableModel );
+  tableModel->setParent( mAttributeTableFilterModel );
+
+  mAttributeTable->setModel( mAttributeTableFilterModel );
+  tableModel->loadLayer();
+  QFont font = mAttributeTable->font();
+  int fontSize = font.pointSize();
+#ifdef Q_OS_WIN
+  fontSize = std::max( fontSize - 1, 8 ); // bit less on windows, due to poor rendering of small point sizes
+#else
+  fontSize = std::max( fontSize - 2, 6 );
+#endif
+  font.setPointSize( fontSize );
+  mAttributeTable->setFont( font );
+
+  // we can safely do this expensive operation here (unlike in the main attribute table), because at most we have only 100 rows...
+  mAttributeTable->resizeColumnsToContents();
+  mAttributeTable->resizeRowsToContents();
+  mAttributeTable->verticalHeader()->setVisible( false ); // maximize valuable table space
+  mAttributeTable->setAlternatingRowColors( true );
+}
+
 QgsBrowserDirectoryProperties::QgsBrowserDirectoryProperties( QWidget *parent )
   : QgsBrowserPropertiesWidget( parent )
 

src/gui/qgsbrowserdockwidget_p.h

@@ -128,7 +128,11 @@ class QgsBrowserLayerProperties : public QgsBrowserPropertiesWidget, private Ui:
     void urlClicked( const QUrl &url );
 
   private:
+
+    void loadAttributeTable();
+
     std::unique_ptr<QgsMapLayer> mLayer;
+    QgsAttributeTableFilterModel *mAttributeTableFilterModel = nullptr;
 
 };
 

src/ui/qgsbrowserlayerpropertiesbase.ui

@@ -71,7 +71,29 @@
         <number>0</number>
        </property>
        <item>
-        <widget class="QgsMapCanvas" name="mMapCanvas" native="true"/>
+        <widget class="QgsMapCanvas" name="mMapCanvas"/>
+       </item>
+      </layout>
+     </widget>
+     <widget class="QWidget" name="mAttributesTab">
+      <attribute name="title">
+       <string>Attributes</string>
+      </attribute>
+      <layout class="QHBoxLayout" name="horizontalLayout_2">
+       <property name="leftMargin">
+        <number>0</number>
+       </property>
+       <property name="topMargin">
+        <number>0</number>
+       </property>
+       <property name="rightMargin">
+        <number>0</number>
+       </property>
+       <property name="bottomMargin">
+        <number>0</number>
+       </property>
+       <item>
+        <widget class="QgsAttributeTableView" name="mAttributeTable"/>
        </item>
       </layout>
      </widget>
@@ -92,10 +114,15 @@
  <customwidgets>
   <customwidget>
    <class>QgsMapCanvas</class>
-   <extends>QWidget</extends>
+   <extends>QGraphicsView</extends>
    <header>qgsmapcanvas.h</header>
    <container>1</container>
   </customwidget>
+  <customwidget>
+   <class>QgsAttributeTableView</class>
+   <extends>QTableView</extends>
+   <header>qgsattributetableview.h</header>
+  </customwidget>
  </customwidgets>
  <resources/>
  <connections/>