qt: Add SubFeeFromAmount option

src/qt/forms/optionsdialog.ui

@@ -200,6 +200,16 @@
        <string>W&amp;allet</string>
       </attribute>
       <layout class="QVBoxLayout" name="verticalLayout_Wallet">
+       <item>
+        <widget class="QCheckBox" name="subFeeFromAmount">
+         <property name="toolTip">
+          <string extracomment="Tooltip text for Options window setting that sets subtracting the fee from a sending amount as default.">Whether to set subtract fee from amount as default or not.</string>
+         </property>
+         <property name="text">
+          <string extracomment="An Options window setting to set subtracting the fee from a sending amount as default.">Subtract &amp;fee from amount by default</string>
+         </property>
+        </widget>
+       </item>
        <item>
         <widget class="QGroupBox" name="groupBox">
          <property name="title">

src/qt/optionsdialog.cpp

@@ -239,6 +239,7 @@ void OptionsDialog::setMapper()
     /* Wallet */
     mapper->addMapping(ui->spendZeroConfChange, OptionsModel::SpendZeroConfChange);
     mapper->addMapping(ui->coinControlFeatures, OptionsModel::CoinControlFeatures);
+    mapper->addMapping(ui->subFeeFromAmount, OptionsModel::SubFeeFromAmount);
     mapper->addMapping(ui->externalSignerPath, OptionsModel::ExternalSignerPath);
 
     /* Network */

src/qt/optionsmodel.cpp

@@ -124,6 +124,11 @@ void OptionsModel::Init(bool resetSettings)
     if (!gArgs.SoftSetArg("-signer", settings.value("external_signer_path").toString().toStdString())) {
         addOverriddenOption("-signer");
     }
+
+    if (!settings.contains("SubFeeFromAmount")) {
+        settings.setValue("SubFeeFromAmount", false);
+    }
+    m_sub_fee_from_amount = settings.value("SubFeeFromAmount", false).toBool();
 #endif
 
     // Network
@@ -335,6 +340,8 @@ QVariant OptionsModel::data(const QModelIndex & index, int role) const
             return settings.value("bSpendZeroConfChange");
         case ExternalSignerPath:
             return settings.value("external_signer_path");
+        case SubFeeFromAmount:
+            return m_sub_fee_from_amount;
 #endif
         case DisplayUnit:
             return nDisplayUnit;
@@ -460,6 +467,10 @@ bool OptionsModel::setData(const QModelIndex & index, const QVariant & value, in
                 setRestartRequired(true);
             }
             break;
+        case SubFeeFromAmount:
+            m_sub_fee_from_amount = value.toBool();
+            settings.setValue("SubFeeFromAmount", m_sub_fee_from_amount);
+            break;
 #endif
         case DisplayUnit:
             setDisplayUnit(value);

src/qt/optionsmodel.h

@@ -61,6 +61,7 @@ public:
         Language,               // QString
         UseEmbeddedMonospacedFont, // bool
         CoinControlFeatures,    // bool
+        SubFeeFromAmount,       // bool
         ThreadsScriptVerif,     // int
         Prune,                  // bool
         PruneSize,              // int
@@ -88,6 +89,7 @@ public:
     QString getThirdPartyTxUrls() const { return strThirdPartyTxUrls; }
     bool getUseEmbeddedMonospacedFont() const { return m_use_embedded_monospaced_font; }
     bool getCoinControlFeatures() const { return fCoinControlFeatures; }
+    bool getSubFeeFromAmount() const { return m_sub_fee_from_amount; }
     const QString& getOverriddenByCommandLine() { return strOverriddenByCommandLine; }
 
     /* Explicit setters */
@@ -112,6 +114,7 @@ private:
     QString strThirdPartyTxUrls;
     bool m_use_embedded_monospaced_font;
     bool fCoinControlFeatures;
+    bool m_sub_fee_from_amount;
     /* settings that were overridden by command-line */
     QString strOverriddenByCommandLine;
 

src/qt/sendcoinsentry.cpp

@@ -97,7 +97,9 @@ void SendCoinsEntry::clear()
     ui->payTo->clear();
     ui->addAsLabel->clear();
     ui->payAmount->clear();
-    ui->checkboxSubtractFeeFromAmount->setCheckState(Qt::Unchecked);
+    if (model && model->getOptionsModel()) {
+        ui->checkboxSubtractFeeFromAmount->setChecked(model->getOptionsModel()->getSubFeeFromAmount());
+    }
     ui->messageTextLabel->clear();
     ui->messageTextLabel->hide();
     ui->messageLabel->hide();