Button validation confirmation

Added confirmation to buttons:

• The back buttons in 1) setting up income and expenses, 2) budget and 3) main menu

Added validation to buttons:

• The next button in budget setup displays an error box if the budget amount has not been used up

src/main/java/no/ntnu/idatt1002/demo/controller/BudgetController.java

@@ -83,10 +83,12 @@ public class BudgetController extends FinanceController {
     private PieChart budgetPieChart;
 
     @FXML
-    private Label daysLeftLbl;
+    private Label disposableAmount;
 
-    BudgetRegister budgetRegister = new BudgetRegister();
+    @FXML
+    private Label amountLeft;
 
+    BudgetRegister budgetRegister;
 
     /**
      * Initializes the budget register, the observable budget list and the tableview, along with the values of the dropbox used for filtering the tableview.
@@ -115,7 +117,7 @@ public class BudgetController extends FinanceController {
                     .readBudgetArchive("budgets/Archive");
             }
 
-            //Refresh piecharts only if the budget is old
+            //Refresh pie charts only if the budget is old
             if (!FileHandlingBudget.isNewBudget(
                 "budgets/" + FileHandlingSelectedBudget.
                     readSelectedBudget("budgets/SelectedBudget") + "/Budget")) {
@@ -125,7 +127,24 @@ public class BudgetController extends FinanceController {
             ioe.printStackTrace();
             showErrorDialogBox(ioe.getMessage(), ioe.getMessage(), ioe.getMessage());
         }
+
+        double maxAmount = general.getMaxAmount();
+        //Set calendar, disposable amount and amount left
         formatDatePicker();
+        disposableAmount.setText(String.valueOf(maxAmount));
+        amountLeft.setText(String.valueOf(maxAmount));
+
+        //Prevent proceeding until all of budget has been used up
+        continueBtn.addEventFilter(
+            ActionEvent.ACTION, event -> {
+                if (maxAmount - general.totalSum() != 0) {
+                    event.consume();
+                    showErrorDialogBox("Use up budget",
+                        "Please distribute the entire disposable amount",
+                        "The amount must be used up before proceeding");
+                }
+            }
+        );
     }
 
     /**
@@ -243,6 +262,7 @@ public class BudgetController extends FinanceController {
         //Updates the tableview and pie chart using the register
         refreshTableView();
         refreshPieChart();
+        refreshAmountLeft();
     }
 
 
@@ -267,6 +287,7 @@ public class BudgetController extends FinanceController {
             general.deleteItemFromBudget(item.getBudgetCategory());
             refreshTableView();
             refreshPieChart();
+            refreshAmountLeft();
         }
     }
 
@@ -279,6 +300,13 @@ public class BudgetController extends FinanceController {
         this.budgetList.setAll(general.getBudgetItems());
     }
 
+    /**
+     * Method for synching the amount left to the sum of budget items in the table view.
+     */
+    private void refreshAmountLeft() {
+        amountLeft.setText(String.valueOf(general.getMaxAmount() - general.totalSum()));
+    }
+
     /**
      * Saves the changes made to the tableview by writing the information to a file.
      *
@@ -304,7 +332,6 @@ public class BudgetController extends FinanceController {
         } catch(IOException ioe) {
             showErrorDialogBox(ioe.getMessage(), ioe.getMessage(), ioe.getMessage());
         }
-
     }
 
     /**
@@ -324,18 +351,26 @@ public class BudgetController extends FinanceController {
             } else if (event.getSource() == continueBtn) {
                 //Adds unused categories to the table
                 general.addUnusedCategories();
+
                 updateBudgetRegister(FileHandlingSelectedBudget
                     .readSelectedBudget("budgets/SelectedBudget"));
+
                 loader.setLocation(getClass().getResource("/view/MainMenuNew.fxml"));
                 //Always saving the data when switching to main menu
                 saveDataToFile();
             } else if (event.getSource() == backBtn) {
-                loader.setLocation(getClass().getResource("/view/dualList.fxml"));
+                Optional<ButtonType> isConfirmed = showConfirmationDialog("Return confirmation"
+                    , "Are you sure you want to go back?","The changes made in this and the previous"
+                        + " window will be reset");
+                if (isConfirmed.isPresent() && isConfirmed.get() == ButtonType.OK) {
+                    loader.setLocation(getClass().getResource("/view/dualList.fxml"));
+                } else return;
             }
             Parent root = loader.load();
             Stage stage = (Stage) ((Node) event.getSource()).getScene().getWindow();
             Scene scene = new Scene(root);
             stage.setScene(scene);
+            stage.setResizable(false);
 
             //Centralize the new screen
             Rectangle2D primScreenBounds = Screen.getPrimary().getVisualBounds();
@@ -343,7 +378,6 @@ public class BudgetController extends FinanceController {
             stage.setY((primScreenBounds.getHeight() - stage.getHeight()) / 2);
 
             stage.show();
-
         } catch(Exception ioe) {
             ioe.printStackTrace();
             showErrorDialogBox("Loading error", "Error in loading", "Could not load"