Cw 171 exchange auto selector bug (#523)

* Fix de-selecting exchange providers not getting saved

* only change field value when the amount is better than the already existing one

* Show calculated amount after getting the best value from all providers

* Catch exceptions to avoid stopping the providers calculate amount APIs

* Fix Splay map only saving the last value obtained

* Show limits for the provider with the highest rate

* Load limits on currency pair change

* Show limits for lowest min provider

* Show limits for lowest min and highest max

* Sync best rate every 10 seconds instead of calculating it on every amount change

* Fix conflicts with flutter upgrade
Add null safety to changes in exchange_view_model.dart

* Remove un-necessary checks

lib/src/screens/exchange/exchange_page.dart

@@ -179,6 +179,7 @@ class ExchangePage extends BasePage {
                             padding: EdgeInsets.fromLTRB(24, 100, 24, 32),
                             child: Observer(
                               builder: (_) => ExchangeCard(
+                                onDispose: disposeBestRateSync,
                                 hasAllAmount: exchangeViewModel.hasAllAmount,
                                 allAmount: exchangeViewModel.hasAllAmount
                                     ? () => exchangeViewModel
@@ -265,6 +266,7 @@ class ExchangePage extends BasePage {
                             EdgeInsets.only(top: 29, left: 24, right: 24),
                             child: Observer(
                                 builder: (_) => ExchangeCard(
+                                  onDispose: disposeBestRateSync,
                                   amountFocusNode: _receiveAmountFocus,
                                   addressFocusNode: _receiveAddressFocus,
                                   key: receiveKey,
@@ -743,13 +745,13 @@ class ExchangePage extends BasePage {
       if (_receiveAmountFocus.hasFocus) {
         exchangeViewModel.isFixedRateMode = true;
       }
-      exchangeViewModel.changeReceiveAmount(amount: receiveAmountController.text);
+      // exchangeViewModel.changeReceiveAmount(amount: receiveAmountController.text);
     });
 
     _depositAmountFocus.addListener(() {
       exchangeViewModel.isFixedRateMode = false;
-      exchangeViewModel.changeDepositAmount(
-        amount: depositAmountController.text);
+      // exchangeViewModel.changeDepositAmount(
+      //   amount: depositAmountController.text);
     });
 
     _isReactionsSet = true;
@@ -791,4 +793,6 @@ class ExchangePage extends BasePage {
     final address = await extractAddressFromParsed(context, parsedAddress);
     return address;
   }
+
+  void disposeBestRateSync() => exchangeViewModel.bestRateSync?.cancel();
 }

lib/src/screens/exchange/widgets/exchange_card.dart

@@ -37,7 +37,8 @@ class ExchangeCard extends StatefulWidget {
       this.addressFocusNode,
       this.allAmount,
       this.onPushPasteButton,
-      this.onPushAddressBookButton})
+      this.onPushAddressBookButton,
+      this.onDispose})
       : super(key: key);
 
   final List<CryptoCurrency> currencies;
@@ -63,6 +64,7 @@ class ExchangeCard extends StatefulWidget {
   final VoidCallback? allAmount;
   final void Function(BuildContext context)? onPushPasteButton;
   final void Function(BuildContext context)? onPushAddressBookButton;
+  final Function()? onDispose;
 
   @override
   ExchangeCardState createState() => ExchangeCardState();
@@ -106,6 +108,13 @@ class ExchangeCardState extends State<ExchangeCard> {
     super.initState();
   }
 
+  @override
+  void dispose() {
+    widget.onDispose?.call();
+
+    super.dispose();
+  }
+
   void changeLimits({String? min, String? max}) {
     setState(() {
       _min = min;