The UWP Notepad Project (Redux): Find/Replace (Premium)

For this installment of our UWP project, we’ll implement Find, Find Next, Find Previous, Replace, and Replace All with a fun new custom dialog.

And I am pretty proud of that dialog. But since I already wrote about how I designed the Find and Replace dialogs as a single ContentDialog back in The UWP Files: Find Your Way Back (Premium), you can read that if you’re interested. The short version is that we display the entire dialog when the user selects the Replace button, but we hide the middle two rows of controls---the “Replace with” textblock and textbox, the Replace button, and the Replace button---when they select the Find button.

To get started, let’s add the code for this new ContentDialog, called FindReplaceDialog, to our XAML. It should go right below the SavePrompt code and look like so:
<ContentDialog x:Name="FindReplaceDialog">
    <Grid Height="Auto" Width="Auto" Margin="0,10,0,0">
        <Grid.RowDefinitions><RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto" />
            <ColumnDefinition Width="Auto" />
            <ColumnDefinition Width="Auto" />
        </Grid.ColumnDefinitions>
        <TextBlock Grid.Row="0" Grid.Column="0" Text="Find what:" HorizontalAlignment="Left" VerticalAlignment="Center" Margin="0,0,10,0" />
        <TextBox Name="FindReplace_FindTextBox" Grid.Row="0" Grid.Column="1" Width="200" Height="32" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="10,0,10,0"  />
        <Button Name="FindReplace_FindButton" Grid.Row="0" Grid.Column="2" Content="Find" Width="110" HorizontalAlignment="Left" VerticalAlignment="Center" Margin="0,0,0,10"/>
        <TextBlock Name="FindReplace_ReplaceWithTextBlock" Grid.Row="1" Grid.Column="0" Text="Replace with:" HorizontalAlignment="Left" VerticalAlignment="Center" Margin="0,0,0,10" />
        <TextBox Name="FindReplace_ReplaceTextBox" Grid.Row="1" Grid.Column="1" Width="200" Height="32" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="10,0,0,10"  />
        <Button Name="FindReplace_ReplaceButton" Grid.Row="1" Grid.Column="2" Content="Replace" Width="110" HorizontalAlignment="Left" VerticalAlignment="Center" Margin="0,0,0,10"/>
        <Button Name="FindReplace_ReplaceAllButton" Grid.Row="2" Grid.Column="2" Content="Replace All" Width="110" HorizontalAlignment="Left" VerticalAlignment="Center" Margin="0,0,0,10"/>
        <Button Name="FindReplace_CancelButton" Grid.Row="3" Grid.Column="2" Content="Close" Width="110" HorizontalAlignment="Le...