Add a new add/edit window

WatchOnlyBitcoinWallet/App.axaml

@@ -15,6 +15,9 @@
     <DataTemplate DataType="{x:Type vm:AboutViewModel}">
       <views:AboutView/>
     </DataTemplate>
+    <DataTemplate DataType="{x:Type vm:AddEditViewModel}">
+      <views:AddEditView/>
+    </DataTemplate>
     <DataTemplate DataType="{x:Type vm:SettingsViewModel}">
       <views:SettingsView/>
     </DataTemplate>

WatchOnlyBitcoinWallet/ViewModels/AddEditViewModel.cs

@@ -0,0 +1,86 @@
+// WatchOnlyBitcoinWallet
+// Copyright (c) 2016 Coding Enthusiast
+// Distributed under the MIT software license, see the accompanying
+// file LICENCE or http://www.opensource.org/licenses/mit-license.php.
+
+using Autarkysoft.Bitcoin;
+using Autarkysoft.Bitcoin.Encoders;
+using WatchOnlyBitcoinWallet.MVVM;
+
+namespace WatchOnlyBitcoinWallet.ViewModels
+{
+    public class AddEditViewModel : ViewModelBase
+    {
+        public AddEditViewModel() : this(string.Empty, string.Empty)
+        {
+        }
+
+        public AddEditViewModel(string addr, string tag)
+        {
+            // Set fields since we don't want to change IsChanged to true.
+            _addr = addr;
+            _tag = tag;
+
+            OkCommand = new(Ok);
+            CancelCommand = new(Cancel);
+        }
+
+
+        public bool IsChanged { get; private set; } = false;
+
+        private string _addr;
+        public string AddressString
+        {
+            get => _addr;
+            set
+            {
+                if (SetField(ref _addr, value))
+                {
+                    IsChanged = true;
+                }
+            }
+        }
+
+        private string _tag;
+        public string Tag
+        {
+            get => _tag;
+            set
+            {
+                if (SetField(ref _tag, value))
+                {
+                    IsChanged = true;
+                }
+            }
+        }
+
+        private string _error = string.Empty;
+        public string Error
+        {
+            get => _error;
+            set => SetField(ref _error, value);
+        }
+
+
+        public BindableCommand OkCommand { get; }
+        private void Ok()
+        {
+            AddressType type = Address.GetAddressType(AddressString, NetworkType.MainNet);
+            if (type is AddressType.Unknown or AddressType.Invalid)
+            {
+                Error = "Invalid address type.";
+            }
+            else
+            {
+                RaiseCloseEvent();
+            }
+        }
+
+        public BindableCommand CancelCommand { get; }
+        private void Cancel()
+        {
+            IsChanged = false;
+            RaiseCloseEvent();
+        }
+    }
+}

WatchOnlyBitcoinWallet/Views/AddEditView.axaml

@@ -0,0 +1,40 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:vm="using:WatchOnlyBitcoinWallet.ViewModels"
+             mc:Ignorable="d"
+             x:Class="WatchOnlyBitcoinWallet.Views.AddEditView"
+             Height="110" Width="480"
+             FontSize="14">
+
+  <Design.DataContext>
+    <vm:AboutViewModel/>
+  </Design.DataContext>
+
+  <Grid ColumnDefinitions="400,*" RowDefinitions="auto,auto,*">
+    <TextBox Text="{Binding AddressString}"
+             Watermark="Enter a valid bitcoin address"
+             Margin="2"
+             Grid.Column="0" Grid.Row="0"/>
+    <TextBox Text="{Binding Tag}"
+             Watermark="[Optional] Enter a name for this address"
+             Margin="2"
+             Grid.Column="0" Grid.Row="1"/>
+    <TextBlock Text="{Binding Error}"
+               Grid.Column="0" Grid.Row="2"/>
+
+    <Button Content="OK"
+            Command="{Binding OkCommand}"
+            HorizontalContentAlignment="Center"
+            IsDefault="True"
+            Width="65"
+            Grid.Column="1" Grid.Row="0"/>
+    <Button Content="Cancel"
+            Command="{Binding CancelCommand}"
+            HorizontalContentAlignment="Center"
+            IsCancel="True"
+            Width="65"
+            Grid.Column="1" Grid.Row="1"/>
+  </Grid>
+</UserControl>

WatchOnlyBitcoinWallet/Views/AddEditView.axaml.cs

@@ -0,0 +1,17 @@
+// WatchOnlyBitcoinWallet
+// Copyright (c) 2016 Coding Enthusiast
+// Distributed under the MIT software license, see the accompanying
+// file LICENCE or http://www.opensource.org/licenses/mit-license.php.
+
+using Avalonia.Controls;
+
+namespace WatchOnlyBitcoinWallet.Views
+{
+    public partial class AddEditView : UserControl
+    {
+        public AddEditView()
+        {
+            InitializeComponent();
+        }
+    }
+}