Enable Button if One of Three Textboxes across 3 tabs has content - wpf

Question

I have a Button that lives outside a tab control element. Each Tab on the TabControl has either a text box for manual text entry or a search tool to look up something from a database (the value of which will also be written to the label in tab 2 & 3).
I want to enable the Print button if the textbox has content or a variable that is populated from a database query on the selected tab has content.
What would be the best way to do this, given a button can only be bound to one source? I pondered having a staging variable, but then that would also be only bound to one element.
Any ideas? I'm really new to data-binding and I'm struggling to get my head around some of the concepts.
It doesn't help that the back-end is in VB because i'm porting a number of WinForms apps to WPF and I want to do them properly.
Quick XAML:
<Window x:Name="Main1" x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" SizeToContent="Height">
<Grid>
<StackPanel >
<Grid x:Name="Activity" Margin="5,5,5,0" >
<StackPanel>
<TabControl x:Name="Main_Tabs" Background="{x:Null}" BorderBrush="Gainsboro">
<TabItem x:Name="T1" Header="H1" >
<Grid Margin="5">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="20*"/>
<ColumnDefinition Width="80*"/>
</Grid.ColumnDefinitions>
<Label Grid.Column="0" Grid.Row="2" HorizontalAlignment="Right">Address:</Label>
<TextBox x:Name="Single_Address"
Margin="5,3"
SpellCheck.IsEnabled="True"
IsManipulationEnabled="True"
TextWrapping="Wrap"
AcceptsReturn="True"
VerticalScrollBarVisibility="Auto"
Grid.Column="1" Grid.Row="2"
Language="en-GB" Height="80">
</TextBox>
</Grid>
</TabItem>
<TabItem x:Name="T2" Header="H2" >
<Grid Grid.ColumnSpan="2" Grid.Row="1" x:Name="Grid_Elucid_Label2">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="20*"/>
<ColumnDefinition Width="80*"/>
</Grid.ColumnDefinitions>
<Label Grid.Column="0" Grid.Row="2" HorizontalAlignment="Right">Address:</Label>
<Label x:Name="Elucid_Address"
Margin="5,3"
Grid.Column="1" Grid.Row="2" Height="80">
</Label>
</Grid>
</TabItem>
<TabItem x:Name="T3" Header="H3">
<Grid x:Name="Grid_Sage_Label" Margin="5">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="20*"/>
<ColumnDefinition Width="80*"/>
</Grid.ColumnDefinitions>
<Label Grid.Column="0" Grid.Row="2" HorizontalAlignment="Right">Address:</Label>
<Label x:Name="Sage_Address" Margin="5,3" Grid.Column="1" Grid.Row="2" Height="80">
</Label>
</Grid>
</TabItem>
</TabControl>
</StackPanel>
</Grid>
<Button x:Name="Print_Button" Content="Print" Padding="10" Background="{x:Null}" BorderBrush="Gainsboro" />
</StackPanel>
</Grid>
</Window>

Answer 1

#1 VM with few textproperties to evaluate
if you have just a few text properties and use a VM, you can go with some triggers.
I wrote this by hand so I'm sorry if the syntax isn't a 100% match.
<button content="print">
<button.style>
<style targettype={x:type button}>
<style.triggers>
<multidatatrigger>
<multidatatrigger.conditions>
<condition Binding="{Binding VMprop1}" Value="">
<condition Binding="{Binding VMprop2}" Value="">
<condition Binding="{Binding VMprop3}" Value="">
</multidatatrigger.conditions>
<multidatatrigger.setters>
<setter property="IsEnabled" value="false"/>
</multidatatrigger.setters>
</multidatatrigger>
</style.triggers>
</style>
</button.style>
<button>
2 no VM or a lot of properties to evaluate
bind to the TextChanged of all TextBoxes and evaluate their state, and set the IsEnabled from your button (if you want use a Dependency Property)
<button x:Name="btn1" content="print" IsEnabled="{Binding CanPrint}"/>
<textbox x:Name="tb1" TextChanged="EvaluateCanPrint"/>
<textbox x:Name="tb2" TextChanged="EvaluateCanPrint"/>
<textbox x:Name="tb3" TextChanged="EvaluateCanPrint"/>
<textbox x:Name="tb4" TextChanged="EvaluateCanPrint"/>
...
private void EvaluateCanPrint() {
// ViewModel.EvaluateCanPrint();
ViewModel.CanPrint =
!string.isNullOrEmpty(tb1.Text) &&
!string.isNullOrEmpty(tb2.Text) &&
...;
}
// Original answer
//private void EvaluateTextChanged() {
// if (string.isNullOrEmpty(tb1.Text) &&
// string.isNullOrEmpty(tb2.Text) &&
// ...)
// {
// btn1.IsEnabled = false;
// }
//}