[qt] Add use available balance in send coins dialog

src/qt/forms/sendcoinsentry.ui

@@ -163,7 +163,7 @@
      </widget>
     </item>
     <item row="2" column="1">
-     <layout class="QHBoxLayout" name="horizontalLayoutAmount" stretch="0,1">
+     <layout class="QHBoxLayout" name="horizontalLayoutAmount" stretch="0,1,0">
       <item>
        <widget class="BitcoinAmountField" name="payAmount"/>
       </item>
@@ -177,6 +177,13 @@
         </property>
        </widget>
       </item>
+      <item>
+       <widget class="QPushButton" name="useAvailableBalanceButton">
+        <property name="text">
+         <string>Use available balance</string>
+        </property>
+       </widget>
+      </item>
      </layout>
     </item>
     <item row="3" column="0">

src/qt/sendcoinsdialog.cpp

@@ -410,6 +410,7 @@ SendCoinsEntry *SendCoinsDialog::addEntry()
     entry->setModel(model);
     ui->entries->addWidget(entry);
     connect(entry, SIGNAL(removeEntry(SendCoinsEntry*)), this, SLOT(removeEntry(SendCoinsEntry*)));
+    connect(entry, SIGNAL(useAvailableBalance(SendCoinsEntry*)), this, SLOT(useAvailableBalance(SendCoinsEntry*)));
     connect(entry, SIGNAL(payAmountChanged()), this, SLOT(coinControlUpdateLabels()));
     connect(entry, SIGNAL(subtractFeeFromAmountChanged()), this, SLOT(coinControlUpdateLabels()));
 
@@ -607,6 +608,31 @@ void SendCoinsDialog::on_buttonMinimizeFee_clicked()
     minimizeFeeSection(true);
 }
 
+void SendCoinsDialog::useAvailableBalance(SendCoinsEntry* entry)
+{
+    // Get CCoinControl instance if CoinControl is enabled or create a new one.
+    CCoinControl coin_control;
+    if (model->getOptionsModel()->getCoinControlFeatures()) {
+        coin_control = *CoinControlDialog::coinControl;
+    }
+
+    // Calculate available amount to send.
+    CAmount amount = model->getBalance(&coin_control);
+    for (int i = 0; i < ui->entries->count(); ++i) {
+        SendCoinsEntry* e = qobject_cast<SendCoinsEntry*>(ui->entries->itemAt(i)->widget());
+        if (e && !e->isHidden() && e != entry) {
+            amount -= e->getValue().amount;
+        }
+    }
+
+    if (amount > 0) {
+      entry->checkSubtractFeeFromAmount();
+      entry->setAmount(amount);
+    } else {
+      entry->setAmount(0);
+    }
+}
+
 void SendCoinsDialog::setMinimumFee()
 {
     ui->radioCustomPerKilobyte->setChecked(true);

src/qt/sendcoinsdialog.h

@@ -76,6 +76,7 @@ private Q_SLOTS:
     void on_buttonChooseFee_clicked();
     void on_buttonMinimizeFee_clicked();
     void removeEntry(SendCoinsEntry* entry);
+    void useAvailableBalance(SendCoinsEntry* entry);
     void updateDisplayUnit();
     void coinControlFeatureChanged(bool);
     void coinControlButtonClicked();

src/qt/sendcoinsentry.cpp

@@ -48,6 +48,7 @@ SendCoinsEntry::SendCoinsEntry(const PlatformStyle *_platformStyle, QWidget *par
     connect(ui->deleteButton, SIGNAL(clicked()), this, SLOT(deleteClicked()));
     connect(ui->deleteButton_is, SIGNAL(clicked()), this, SLOT(deleteClicked()));
     connect(ui->deleteButton_s, SIGNAL(clicked()), this, SLOT(deleteClicked()));
+    connect(ui->useAvailableBalanceButton, SIGNAL(clicked()), this, SLOT(useAvailableBalanceClicked()));
 }
 
 SendCoinsEntry::~SendCoinsEntry()
@@ -112,11 +113,21 @@ void SendCoinsEntry::clear()
     updateDisplayUnit();
 }
 
+void SendCoinsEntry::checkSubtractFeeFromAmount()
+{
+    ui->checkboxSubtractFeeFromAmount->setChecked(true);
+}
+
 void SendCoinsEntry::deleteClicked()
 {
     Q_EMIT removeEntry(this);
 }
 
+void SendCoinsEntry::useAvailableBalanceClicked()
+{
+    Q_EMIT useAvailableBalance(this);
+}
+
 bool SendCoinsEntry::validate()
 {
     if (!model)
@@ -228,6 +239,11 @@ void SendCoinsEntry::setAddress(const QString &address)
     ui->payAmount->setFocus();
 }
 
+void SendCoinsEntry::setAmount(const CAmount &amount)
+{
+    ui->payAmount->setValue(amount);
+}
+
 bool SendCoinsEntry::isClear()
 {
     return ui->payTo->text().isEmpty() && ui->payTo_is->text().isEmpty() && ui->payTo_s->text().isEmpty();

src/qt/sendcoinsentry.h

@@ -38,6 +38,7 @@ public:
 
     void setValue(const SendCoinsRecipient &value);
     void setAddress(const QString &address);
+    void setAmount(const CAmount &amount);
 
     /** Set up the tab chain manually, as Qt messes up the tab chain by default in some cases
      *  (issue https://bugreports.qt-project.org/browse/QTBUG-10907).
@@ -48,14 +49,17 @@ public:
 
 public Q_SLOTS:
     void clear();
+    void checkSubtractFeeFromAmount();
 
 Q_SIGNALS:
     void removeEntry(SendCoinsEntry *entry);
+    void useAvailableBalance(SendCoinsEntry* entry);
     void payAmountChanged();
     void subtractFeeFromAmountChanged();
 
 private Q_SLOTS:
     void deleteClicked();
+    void useAvailableBalanceClicked();
     void on_payTo_textChanged(const QString &address);
     void on_addressBookButton_clicked();
     void on_pasteButton_clicked();