Fix missing SVG previews for existing composer picture item

- Previews now load when picture is first selected and its properties are shown (unless already loaded)
- NOTE: the loading of SVGs per QListWidget per picture should be replaced with a model/view per composer, or something cached
- Combobox no longer over-expands width of dock widget when it contains long paths

src/app/composer/qgscomposerpicturewidget.cpp

@@ -39,6 +39,7 @@ QgsComposerPictureWidget::QgsComposerPictureWidget( QgsComposerPicture* picture
   mainLayout->addWidget( itemPropertiesWidget );
 
   setGuiElementValues();
+  mPreviewsLoadingLabel->hide();
 
   mPreviewListWidget->setIconSize( QSize( 30, 30 ) );
 
@@ -487,5 +488,20 @@ void QgsComposerPictureWidget::showEvent( QShowEvent * event )
 {
   Q_UNUSED( event );
   refreshMapComboBox();
+
+  if ( mPreviewListWidget->count() == 0 )
+  {
+    mPreviewListWidget->hide();
+    mPreviewsLoadingLabel->show();
+    addStandardDirectoriesToPreview();
+    mPreviewsLoadingLabel->hide();
+    mPreviewListWidget->show();
+  }
+}
+
+void QgsComposerPictureWidget::resizeEvent( QResizeEvent * event )
+{
+  Q_UNUSED( event );
+  mSearchDirectoriesComboBox->setMinimumWidth( mPreviewListWidget->sizeHint().width() );
 }
 

src/app/composer/qgscomposerpicturewidget.h

@@ -48,6 +48,7 @@ class QgsComposerPictureWidget: public QWidget, private Ui::QgsComposerPictureWi
 
   protected:
     void showEvent( QShowEvent * event );
+    void resizeEvent( QResizeEvent * event );
 
   private slots:
     /**Sets the GUI elements to the values of mPicture*/

src/ui/qgscomposerpicturewidgetbase.ui

@@ -68,25 +68,19 @@
          <property name="collapsed" stdset="0">
           <bool>false</bool>
          </property>
-         <layout class="QFormLayout" name="formLayout_2">
-          <property name="fieldGrowthPolicy">
-           <enum>QFormLayout::AllNonFixedFieldsGrow</enum>
-          </property>
-          <property name="labelAlignment">
-           <set>Qt::AlignLeading|Qt::AlignLeft|Qt::AlignVCenter</set>
-          </property>
-          <item row="1" column="0">
-           <widget class="QLabel" name="label">
-            <property name="text">
-             <string>Path</string>
-            </property>
-            <property name="buddy">
-             <cstring>mPictureLineEdit</cstring>
-            </property>
-           </widget>
-          </item>
-          <item row="1" column="1">
+         <layout class="QVBoxLayout" name="verticalLayout_3">
+          <item>
            <layout class="QHBoxLayout" name="horizontalLayout_2">
+            <item>
+             <widget class="QLabel" name="label">
+              <property name="text">
+               <string>Path</string>
+              </property>
+              <property name="buddy">
+               <cstring>mPictureLineEdit</cstring>
+              </property>
+             </widget>
+            </item>
             <item>
              <widget class="QLineEdit" name="mPictureLineEdit"/>
             </item>
@@ -132,6 +126,24 @@
           <bool>false</bool>
          </property>
          <layout class="QVBoxLayout" name="verticalLayout">
+          <item>
+           <widget class="QLabel" name="mPreviewsLoadingLabel">
+            <property name="font">
+             <font>
+              <italic>true</italic>
+             </font>
+            </property>
+            <property name="styleSheet">
+             <string notr="true">color: rgb(19, 133, 54);</string>
+            </property>
+            <property name="text">
+             <string>Loading SVG previews...</string>
+            </property>
+            <property name="alignment">
+             <set>Qt::AlignCenter</set>
+            </property>
+           </widget>
+          </item>
           <item>
            <widget class="QListWidget" name="mPreviewListWidget">
             <property name="showDropIndicator" stdset="0">
@@ -167,7 +179,11 @@
            </widget>
           </item>
           <item>
-           <widget class="QComboBox" name="mSearchDirectoriesComboBox"/>
+           <widget class="QComboBox" name="mSearchDirectoriesComboBox">
+            <property name="sizeAdjustPolicy">
+             <enum>QComboBox::AdjustToMinimumContentsLength</enum>
+            </property>
+           </widget>
           </item>
           <item>
            <layout class="QHBoxLayout" name="horizontalLayout">