Add placeholder text for empty views

Throughout our QML-based software, we now display placeholder text for
empty views so that the user knows that the view is actually empty, and
it's not that the software is just broken.

This commit introduces the same thing for Dolphin's main view.

BUG: 429248
BUG: 426354
FIXED-IN: 21.04

src/views/dolphinview.cpp

@@ -48,7 +48,9 @@
 #include <QApplication>
 #include <QClipboard>
 #include <QDropEvent>
+#include <QGraphicsOpacityEffect>
 #include <QGraphicsSceneDragDropEvent>
+#include <QLabel>
 #include <QMenu>
 #include <QMimeDatabase>
 #include <QPixmapCache>
@@ -82,7 +84,8 @@ DolphinView::DolphinView(const QUrl& url, QWidget* parent) :
     m_clearSelectionBeforeSelectingNewItems(false),
     m_markFirstNewlySelectedItemAsCurrent(false),
     m_versionControlObserver(nullptr),
-    m_twoClicksRenamingTimer(nullptr)
+    m_twoClicksRenamingTimer(nullptr),
+    m_placeholderLabel(nullptr)
 {
     m_topLayout = new QVBoxLayout(this);
     m_topLayout->setSpacing(0);
@@ -120,6 +123,29 @@ DolphinView::DolphinView(const QUrl& url, QWidget* parent) :
     connect(m_container->horizontalScrollBar(), &QScrollBar::valueChanged, this, [=] { hideToolTip(); });
     connect(m_container->verticalScrollBar(), &QScrollBar::valueChanged, this, [=] { hideToolTip(); });
 
+    // Show some placeholder text for empty folders
+    // This is made using a heavily-modified QLabel rather than a KTitleWidget
+    // because KTitleWidget can't be told to turn off mouse-selectable text
+    m_placeholderLabel = new QLabel(this);
+    QFont placeholderLabelFont;
+    // To match the size of a level 2 Heading/KTitleWidget
+    placeholderLabelFont.setPointSize(qRound(placeholderLabelFont.pointSize() * 1.3));
+    m_placeholderLabel->setFont(placeholderLabelFont);
+    m_placeholderLabel->setTextInteractionFlags(Qt::NoTextInteraction);
+    m_placeholderLabel->setWordWrap(true);
+    m_placeholderLabel->setAlignment(Qt::AlignCenter);
+    // Match opacity of QML placeholder label component
+    auto *effect = new QGraphicsOpacityEffect(m_placeholderLabel);
+    effect->setOpacity(0.5);
+    m_placeholderLabel->setGraphicsEffect(effect);
+    // Set initial text and visibility
+    updatePlaceholderLabel();
+    // Add a new layout to hold it and put it in the layout
+    auto *centeringLayout = new QVBoxLayout(this);
+    m_container->setLayout(centeringLayout);
+    centeringLayout->addWidget(m_placeholderLabel);
+    centeringLayout->setAlignment(m_placeholderLabel, Qt::AlignCenter);
+
     controller->setSelectionBehavior(KItemListController::MultiSelection);
     connect(controller, &KItemListController::itemActivated, this, &DolphinView::slotItemActivated);
     connect(controller, &KItemListController::itemsActivated, this, &DolphinView::slotItemsActivated);
@@ -152,6 +178,11 @@ DolphinView::DolphinView(const QUrl& url, QWidget* parent) :
     connect(m_model, &KFileItemModel::directoryRedirection, this, &DolphinView::slotDirectoryRedirection);
     connect(m_model, &KFileItemModel::urlIsFileError,            this, &DolphinView::urlIsFileError);
 
+    connect(this, &DolphinView::itemCountChanged,
+            this, &DolphinView::updatePlaceholderLabel);
+    connect(this, &DolphinView::urlChanged,
+            this, &DolphinView::updatePlaceholderLabel);
+
     m_view->installEventFilter(this);
     connect(m_view, &DolphinItemListView::sortOrderChanged,
             this, &DolphinView::slotSortOrderChangedByHeader);
@@ -1594,6 +1625,9 @@ void DolphinView::slotRenamingResult(KJob* job)
 
 void DolphinView::slotDirectoryLoadingStarted()
 {
+    // We don't want the placeholder label to flicker while the folder is loading
+    m_placeholderLabel->setVisible(false);
+
     // Disable the writestate temporary until it can be determined in a fast way
     // in DolphinView::slotDirectoryLoadingCompleted()
     if (m_isFolderWritable) {
@@ -1610,8 +1644,12 @@ void DolphinView::slotDirectoryLoadingCompleted()
     // because the view might not be in its final state yet.
     QTimer::singleShot(0, this, &DolphinView::updateViewState);
 
+    // Update the placeholder label in case we found that the folder was empty
+    // after loading it
+
     Q_EMIT directoryLoadingCompleted();
 
+    updatePlaceholderLabel();
     updateWritableState();
 }
 
@@ -1976,3 +2014,35 @@ void DolphinView::slotSwipeUp()
 {
     Q_EMIT goUpRequested();
 }
+
+void DolphinView::updatePlaceholderLabel()
+{
+    if (itemsCount() > 0) {
+        m_placeholderLabel->setVisible(false);
+        return;
+    }
+
+    if (!nameFilter().isEmpty()) {
+        m_placeholderLabel->setText(i18n("No items matching the filter"));
+    } else if (m_url.scheme() == QLatin1String("baloosearch") || m_url.scheme() == QLatin1String("filenamesearch")) {
+        m_placeholderLabel->setText(i18n("No items matching the search"));
+    } else if (m_url.scheme() == QLatin1String("trash")) {
+        m_placeholderLabel->setText(i18n("Trash is empty"));
+    } else if (m_url.scheme() == QLatin1String("tags")) {
+        m_placeholderLabel->setText(i18n("No tags"));
+    } else if (m_url.scheme() == QLatin1String("recentlyused")) {
+        m_placeholderLabel->setText(i18n("No recently used items"));
+    } else if (m_url.scheme() == QLatin1String("smb")) {
+        m_placeholderLabel->setText(i18n("No shared folders found"));
+    } else if (m_url.scheme() == QLatin1String("network")) {
+        m_placeholderLabel->setText(i18n("No relevant network resources found"));
+    } else if (m_url.scheme() == QLatin1String("mtp")) {
+        m_placeholderLabel->setText(i18n("No MTP-compatible devices found"));
+    } else if (m_url.scheme() == QLatin1String("bluetooth")) {
+        m_placeholderLabel->setText(i18n("No Bluetooth devices found"));
+    } else {
+        m_placeholderLabel->setText(i18n("Folder is empty"));
+    }
+
+    m_placeholderLabel->setVisible(true);
+}

src/views/dolphinview.h

@@ -32,6 +32,7 @@ class KItemSet;
 class ToolTipManager;
 class VersionControlObserver;
 class ViewProperties;
+class QLabel;
 class QGraphicsSceneDragDropEvent;
 class QRegularExpression;
 
@@ -804,6 +805,8 @@ private:
 
     void abortTwoClicksRenaming();
 
+    void updatePlaceholderLabel();
+
 private:
     void updatePalette();
 
@@ -841,6 +844,7 @@ private:
 
     QTimer* m_twoClicksRenamingTimer;
     QUrl m_twoClicksRenamingItemUrl;
+    QLabel* m_placeholderLabel;
 
     // For unit tests
     friend class TestBase;