qt: Use QVariant instead of int for BitcoinUnit in QSettings

This change improves type safety.

src/qt/bitcoin.cpp

@@ -95,6 +95,8 @@ static void RegisterMetaTypes()
     qRegisterMetaType<std::function<void()>>("std::function<void()>");
     qRegisterMetaType<QMessageBox::Icon>("QMessageBox::Icon");
     qRegisterMetaType<interfaces::BlockAndHeaderTipInfo>("interfaces::BlockAndHeaderTipInfo");
+
+    qRegisterMetaTypeStreamOperators<BitcoinUnit>("BitcoinUnit");
 }
 
 static QString GetLangTerritory()

src/qt/bitcoinunits.cpp

@@ -250,3 +250,40 @@ CAmount BitcoinUnits::maxMoney()
 {
     return MAX_MONEY;
 }
+
+namespace {
+qint8 ToQint8(BitcoinUnit unit)
+{
+    switch (unit) {
+    case BitcoinUnits::BTC: return 0;
+    case BitcoinUnits::mBTC: return 1;
+    case BitcoinUnits::uBTC: return 2;
+    case BitcoinUnits::SAT: return 3;
+    } // no default case, so the compiler can warn about missing cases
+    assert(false);
+}
+
+BitcoinUnit FromQint8(qint8 num)
+{
+    switch (num) {
+    case 0: return BitcoinUnits::BTC;
+    case 1: return BitcoinUnits::mBTC;
+    case 2: return BitcoinUnits::uBTC;
+    case 3: return BitcoinUnits::SAT;
+    }
+    assert(false);
+}
+} // namespace
+
+QDataStream& operator<<(QDataStream& out, const BitcoinUnit& unit)
+{
+    return out << ToQint8(unit);
+}
+
+QDataStream& operator>>(QDataStream& in, BitcoinUnit& unit)
+{
+    qint8 input;
+    in >> input;
+    unit = FromQint8(input);
+    return in;
+}

src/qt/bitcoinunits.h

@@ -8,6 +8,7 @@
 #include <consensus/amount.h>
 
 #include <QAbstractListModel>
+#include <QDataStream>
 #include <QString>
 
 // U+2009 THIN SPACE = UTF-8 E2 80 89
@@ -45,6 +46,7 @@ public:
         uBTC,
         SAT
     };
+    Q_ENUM(Unit)
 
     enum class SeparatorStyle
     {
@@ -111,4 +113,7 @@ private:
 };
 typedef BitcoinUnits::Unit BitcoinUnit;
 
+QDataStream& operator<<(QDataStream& out, const BitcoinUnit& unit);
+QDataStream& operator>>(QDataStream& in, BitcoinUnit& unit);
+
 #endif // BITCOIN_QT_BITCOINUNITS_H

src/qt/optionsmodel.cpp

@@ -24,6 +24,7 @@
 #include <QLatin1Char>
 #include <QSettings>
 #include <QStringList>
+#include <QVariant>
 
 const char *DEFAULT_GUI_PROXY_HOST = "127.0.0.1";
 
@@ -71,9 +72,16 @@ void OptionsModel::Init(bool resetSettings)
     fMinimizeOnClose = settings.value("fMinimizeOnClose").toBool();
 
     // Display
-    if (!settings.contains("nDisplayUnit"))
-        settings.setValue("nDisplayUnit", BitcoinUnits::BTC);
-    nDisplayUnit = settings.value("nDisplayUnit").toInt();
+    if (!settings.contains("DisplayBitcoinUnit")) {
+        settings.setValue("DisplayBitcoinUnit", QVariant::fromValue(BitcoinUnit::BTC));
+    }
+    QVariant unit = settings.value("DisplayBitcoinUnit");
+    if (unit.canConvert<BitcoinUnit>()) {
+        m_display_bitcoin_unit = unit.value<BitcoinUnit>();
+    } else {
+        m_display_bitcoin_unit = BitcoinUnit::BTC;
+        settings.setValue("DisplayBitcoinUnit", QVariant::fromValue(m_display_bitcoin_unit));
+    }
 
     if (!settings.contains("strThirdPartyTxUrls"))
         settings.setValue("strThirdPartyTxUrls", "");
@@ -356,7 +364,7 @@ QVariant OptionsModel::data(const QModelIndex & index, int role) const
             return m_sub_fee_from_amount;
 #endif
         case DisplayUnit:
-            return nDisplayUnit;
+            return QVariant::fromValue(m_display_bitcoin_unit);
         case ThirdPartyTxUrls:
             return strThirdPartyTxUrls;
         case Language:
@@ -567,12 +575,11 @@ bool OptionsModel::setData(const QModelIndex & index, const QVariant & value, in
 /** Updates current unit in memory, settings and emits displayUnitChanged(newUnit) signal */
 void OptionsModel::setDisplayUnit(const QVariant &value)
 {
-    if (!value.isNull())
-    {
+    if (!value.isNull()) {
         QSettings settings;
-        nDisplayUnit = value.toInt();
-        settings.setValue("nDisplayUnit", nDisplayUnit);
-        Q_EMIT displayUnitChanged(nDisplayUnit);
+        m_display_bitcoin_unit = value.value<BitcoinUnit>();
+        settings.setValue("DisplayBitcoinUnit", QVariant::fromValue(m_display_bitcoin_unit));
+        Q_EMIT displayUnitChanged(static_cast<int>(m_display_bitcoin_unit));
     }
 }
 

src/qt/optionsmodel.h

@@ -6,6 +6,7 @@
 #define BITCOIN_QT_OPTIONSMODEL_H
 
 #include <cstdint>
+#include <qt/bitcoinunits.h>
 #include <qt/guiconstants.h>
 
 #include <QAbstractListModel>
@@ -86,7 +87,7 @@ public:
     bool getShowTrayIcon() const { return m_show_tray_icon; }
     bool getMinimizeToTray() const { return fMinimizeToTray; }
     bool getMinimizeOnClose() const { return fMinimizeOnClose; }
-    int getDisplayUnit() const { return nDisplayUnit; }
+    int getDisplayUnit() const { return static_cast<int>(m_display_bitcoin_unit); }
     QString getThirdPartyTxUrls() const { return strThirdPartyTxUrls; }
     bool getUseEmbeddedMonospacedFont() const { return m_use_embedded_monospaced_font; }
     bool getCoinControlFeatures() const { return fCoinControlFeatures; }
@@ -112,7 +113,7 @@ private:
     bool fMinimizeToTray;
     bool fMinimizeOnClose;
     QString language;
-    int nDisplayUnit;
+    BitcoinUnit m_display_bitcoin_unit;
     QString strThirdPartyTxUrls;
     bool m_use_embedded_monospaced_font;
     bool fCoinControlFeatures;