qt: Use fixed-point arithmetic in amount spinbox

Fixes various issues and cleans up code

- Fixes issue #4500: Amount widget +/- has floating point rounding artifacts
- Amount box can now be emptied again, without clearing to 0

Also aligns the amount to the right, as in other places.

1 files changed, 8 insertions, 1 deletions

diff --git a/src/qt/sendcoinsentry.cpp b/src/qt/sendcoinsentry.cpp
index e0f56f8cd..3c0b8881f 100644
--- a/src/qt/sendcoinsentry.cpp
+++ b/src/qt/sendcoinsentry.cpp
@@ -72,7 +72,7 @@ void SendCoinsEntry::setModel(WalletModel *model)
     if (model && model->getOptionsModel())
         connect(model->getOptionsModel(), SIGNAL(displayUnitChanged(int)), this, SLOT(updateDisplayUnit()));
 
-    connect(ui->payAmount, SIGNAL(textChanged()), this, SIGNAL(payAmountChanged()));
+    connect(ui->payAmount, SIGNAL(valueChanged()), this, SIGNAL(payAmountChanged()));
     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()));
@@ -130,6 +130,13 @@ bool SendCoinsEntry::validate()
         retval = false;
     }
 
+    // Sending a zero amount is invalid
+    if (ui->payAmount->value(0) <= 0)
+    {
+        ui->payAmount->setValid(false);
+        retval = false;
+    }
+
     // Reject dust outputs:
     if (retval && GUIUtil::isDust(ui->payTo->text(), ui->payAmount->value())) {
         ui->payAmount->setValid(false);