Added the NewControl as a content replacement for the MainWindow.

PcgsInvUi/ViewModels/EditViewModel.cs

@@ -0,0 +1,30 @@
+using System;
+using System.Reactive;
+using PcgsInvUi.Models;
+using ReactiveUI;
+
+namespace PcgsInvUi.ViewModels;
+
+public class EditViewModel : ViewModelBase
+{
+    public Coin CurrentCoin { get; set; }
+    
+    public ReactiveCommand<Unit, Unit> OkCommand { get; }
+
+    public EditViewModel(Coin coin)
+    {
+        CurrentCoin = coin;
+
+        var okEnabled = this.WhenAnyValue(
+            x => x.CurrentCoin.PcgsNumber,
+            x => x.CurrentCoin.Grade,
+            x => x.CurrentCoin.Quantity,
+            (id, grade, quantity) => (id != 0) &&
+                                     !string.IsNullOrWhiteSpace(grade) &&
+                                     (quantity != 0)
+        );
+        
+        // Setup OkCommand - all Coin-related properties must be non-whitespace.
+        OkCommand = ReactiveCommand.Create(() => { });
+    }
+}