qt: Add GUIUtil::ThemedLabel class

The ThemedLabel class correctly handles appearance changes on macOS.

src/qt/guiutil.cpp

@@ -6,6 +6,7 @@
 
 #include <qt/bitcoinaddressvalidator.h>
 #include <qt/bitcoinunits.h>
+#include <qt/platformstyle.h>
 #include <qt/qvalidatedlineedit.h>
 #include <qt/sendcoinsrecipient.h>
 
@@ -61,6 +62,7 @@
 #include <QUrlQuery>
 #include <QtGlobal>
 
+#include <cassert>
 #include <chrono>
 
 #if defined(Q_OS_MAC)
@@ -786,6 +788,35 @@ qreal calculateIdealFontSize(int width, const QString& text, QFont font, qreal m
     return font_size;
 }
 
+ThemedLabel::ThemedLabel(const PlatformStyle* platform_style, QWidget* parent)
+    : QLabel{parent}, m_platform_style{platform_style}
+{
+    assert(m_platform_style);
+}
+
+void ThemedLabel::setThemedPixmap(const QString& image_filename, int width, int height)
+{
+    m_image_filename = image_filename;
+    m_pixmap_width = width;
+    m_pixmap_height = height;
+    updateThemedPixmap();
+}
+
+void ThemedLabel::changeEvent(QEvent* e)
+{
+#ifdef Q_OS_MACOS
+    if (e->type() == QEvent::PaletteChange) {
+        updateThemedPixmap();
+    }
+#endif
+    QLabel::changeEvent(e);
+}
+
+void ThemedLabel::updateThemedPixmap()
+{
+    setPixmap(m_platform_style->SingleColorIcon(m_image_filename).pixmap(m_pixmap_width, m_pixmap_height));
+}
+
 void ClickableLabel::mouseReleaseEvent(QMouseEvent *event)
 {
     Q_EMIT clicked(event->pos());

src/qt/guiutil.h

@@ -27,6 +27,7 @@
 #include <chrono>
 #include <utility>
 
+class PlatformStyle;
 class QValidatedLineEdit;
 class SendCoinsRecipient;
 
@@ -221,6 +222,25 @@ namespace GUIUtil
 
     qreal calculateIdealFontSize(int width, const QString& text, QFont font, qreal minPointSize = 4, qreal startPointSize = 14);
 
+    class ThemedLabel : public QLabel
+    {
+        Q_OBJECT
+
+    public:
+        explicit ThemedLabel(const PlatformStyle* platform_style, QWidget* parent = nullptr);
+        void setThemedPixmap(const QString& image_filename, int width, int height);
+
+    protected:
+        void changeEvent(QEvent* e) override;
+
+    private:
+        const PlatformStyle* m_platform_style;
+        QString m_image_filename;
+        int m_pixmap_width;
+        int m_pixmap_height;
+        void updateThemedPixmap();
+    };
+
     class ClickableLabel : public QLabel
     {
         Q_OBJECT