Fixes for backups for Android. Fixes for send almost all amount.

lib/bitcoin/bitcoin_wallet.dart

@@ -261,14 +261,20 @@ abstract class BitcoinWalletBase extends WalletBase<BitcoinBalance> with Store {
   @override
   Future<PendingBitcoinTransaction> createTransaction(
       Object credentials) async {
+    const minAmount = 546;
     final transactionCredentials = credentials as BitcoinTransactionCredentials;
     final inputs = <BitcoinUnspent>[];
     final allAmountFee =
         calculateEstimatedFee(transactionCredentials.priority, null);
+    final allAmount = balance.confirmed - allAmountFee;
     var fee = 0;
-    final amount = transactionCredentials.amount != null
+    final credentialsAmount = transactionCredentials.amount != null
         ? stringDoubleToBitcoinAmount(transactionCredentials.amount)
-        : balance.confirmed - allAmountFee;
+        : 0;
+    final amount = transactionCredentials.amount == null ||
+            allAmount - credentialsAmount < minAmount
+        ? allAmount
+        : credentialsAmount;
     final txb = bitcoin.TransactionBuilder(network: bitcoin.bitcoin);
     final changeAddress = address;
     var leftAmount = amount;
@@ -294,8 +300,8 @@ abstract class BitcoinWalletBase extends WalletBase<BitcoinBalance> with Store {
 
     final totalAmount = amount + fee;
     fee = transactionCredentials.amount != null
-        ? feeAmountForPriority(
-            transactionCredentials.priority, inputs.length, 2)
+        ? feeAmountForPriority(transactionCredentials.priority, inputs.length,
+            amount == allAmount ? 1 : 2)
         : allAmountFee;
 
     if (totalAmount > balance.confirmed) {
@@ -329,7 +335,7 @@ abstract class BitcoinWalletBase extends WalletBase<BitcoinBalance> with Store {
     final feeAmount = transactionCredentials.priority.rate * estimatedSize;
     final changeValue = totalInputAmount - amount - feeAmount;
 
-    if (changeValue > 0) {
+    if (changeValue > minAmount) {
       txb.addOutput(changeAddress, changeValue);
     }
 
@@ -375,8 +381,9 @@ abstract class BitcoinWalletBase extends WalletBase<BitcoinBalance> with Store {
       } else {
         inputsCount = _unspent.length;
       }
-
-      return feeAmountForPriority(priority, inputsCount, 2);
+      // If send all, then we have no change value
+      return feeAmountForPriority(
+          priority, inputsCount, amount != null ? 2 : 1);
     }
 
     return 0;

lib/src/screens/backup/backup_page.dart

@@ -14,6 +14,7 @@ import 'package:cake_wallet/utils/show_pop_up.dart';
 import 'package:cake_wallet/view_model/backup_view_model.dart';
 import 'package:cake_wallet/core/execution_state.dart';
 import 'package:cake_wallet/src/screens/base_page.dart';
+import 'package:permission_handler/permission_handler.dart';
 
 class BackupPage extends BasePage {
   BackupPage(this.backupViewModelBase);
@@ -99,8 +100,6 @@ class BackupPage extends BasePage {
               actionRightButton: () async {
                 Navigator.of(dialogContext).pop();
                 final backup = await backupViewModelBase.exportBackup();
-                await backupViewModelBase.saveToDownload(
-                    backup.name, backup.content);
 
                 if (Platform.isAndroid) {
                   onExportAndroid(context, backup);
@@ -123,9 +122,16 @@ class BackupPage extends BasePage {
               rightButtonText: 'Save to Downloads',
               leftButtonText: 'Share',
               actionRightButton: () async {
-                Navigator.of(dialogContext).pop();
+                final permission = await Permission.storage.request();
+
+                if (permission.isDenied) {
+                  Navigator.of(dialogContext).pop();
+                  return;
+                }
+
                 await backupViewModelBase.saveToDownload(
                     backup.name, backup.content);
+                Navigator.of(dialogContext).pop();
               },
               actionLeftButton: () {
                 Navigator.of(dialogContext).pop();

lib/src/screens/exchange_trade/exchange_trade_page.dart

@@ -255,11 +255,11 @@ class ExchangeTradeState extends State<ExchangeTradeForm> {
                         .pendingTransaction.feeFormatted,
                     rightButtonText: S.of(context).ok,
                     leftButtonText: S.of(context).cancel,
-                    actionRightButton: () {
+                    actionRightButton: () async {
                       Navigator.of(context).pop();
-                      widget.exchangeTradeViewModel.sendViewModel
+                      await widget.exchangeTradeViewModel.sendViewModel
                           .commitTransaction();
-                      showPopUp<void>(
+                      await showPopUp<void>(
                           context: context,
                           builder: (BuildContext context) {
                             return Observer(builder: (_) {
@@ -359,10 +359,10 @@ class ExchangeTradeState extends State<ExchangeTradeForm> {
                           });
                     },
                     actionLeftButton: () => Navigator.of(context).pop(),
-                    feeFiatAmount: widget.exchangeTradeViewModel.sendViewModel
-                        .pendingTransaction.feeFormatted,
+                    feeFiatAmount: widget.exchangeTradeViewModel.sendViewModel.pendingTransactionFeeFiatAmount
+                        +  ' ' + widget.exchangeTradeViewModel.sendViewModel.fiat.title,
                     fiatAmountValue: widget.exchangeTradeViewModel.sendViewModel
-                            .pendingTransactionFeeFiatAmount +
+                            .pendingTransactionFiatAmount +
                         ' ' +
                         widget.exchangeTradeViewModel.sendViewModel.fiat.title,
                     recipientTitle: S.of(context).recipient_address,

lib/view_model/backup_view_model.dart

@@ -1,5 +1,4 @@
 import 'dart:io';
-
 import 'package:cake_wallet/core/backup_service.dart';
 import 'package:cake_wallet/core/execution_state.dart';
 import 'package:cake_wallet/entities/secret_store_key.dart';
@@ -7,6 +6,7 @@ import 'package:cake_wallet/store/secret_store.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter_secure_storage/flutter_secure_storage.dart';
 import 'package:mobx/mobx.dart';
+import 'package:intl/intl.dart';
 
 part 'backup_view_model.g.dart';
 
@@ -56,9 +56,11 @@ abstract class BackupViewModelBase with Store {
       state = IsExecutingState();
       final backupContent = await backupService.exportBackup(backupPassword);
       state = ExecutedSuccessfullyState();
+      final now = DateTime.now();
+      final formatter = DateFormat('yyyy-MM-dd_Hm');
 
       return BackupExportFile(backupContent.toList(),
-          name: 'backup_${DateTime.now().toString()}.zip');
+          name: 'cake_wallet_backup_${formatter.format(now)}');
     } catch (e) {
       print(e.toString());
       state = FailureState(e.toString());

lib/view_model/send/send_view_model.dart

@@ -167,6 +167,7 @@ abstract class SendViewModelBase with Store {
 
   Validator get templateValidator => TemplateValidator();
 
+  @observable
   PendingTransaction pendingTransaction;
 
   @computed