Question

<Window x:Class="Binding2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <StackPanel Orientation="Vertical">
        <StackPanel HorizontalAlignment="Left" Name="stackPanel1" VerticalAlignment="Top" Width="165" Orientation="Horizontal">
            <TextBlock Height="20" Name="_sourceTextBlock" Text="Source" Width="67" />
            <TextBox Height="20" Name="_sourceTextBox" Width="92" />
        </StackPanel>
        <StackPanel HorizontalAlignment="Left" Name="stackPanel2" VerticalAlignment="Top" Width="165" Orientation="Horizontal">
            <TextBlock Height="20" Name="_destTextBlock" Text="Destination" Width="67" />
            <TextBox Height="20" Name="_destTextBox" Width="92" />
        </StackPanel>
    </StackPanel>
</Window>

I have two text boxes. How can I program that the value in Destination text box is automatically modified based on the value in Source text box? For example, when the value in Source is “abc”, how can I make the value in Destination is automaticaly “x” + “abc” + “x”? Or, make destination the number 10*source.

ADDED

I also found a way to get the result when the source is more than one – Bind an element to two sources

Answer 1

That’s easy using MVVM :

public class MainWindowViewModel : ViewModelBase
{
    private string _source;
    public string Source
    {
        get { return _source; }
        set
        {
            _source = value;
            OnPropertyChanged("Source");
            OnPropertyChanged("Destination");
        }
    }

    public string Destination
    {
        get { return "x" + _source + "x"; }
    }

}

Use that class as the DataContext for your view, and bind one TextBox to Source (TwoWay), and the other to Destination (OneWay):

<StackPanel Orientation="Vertical">
    <StackPanel HorizontalAlignment="Left" Name="stackPanel1" VerticalAlignment="Top" Width="165" Orientation="Horizontal">
        <TextBlock Height="20" Name="_sourceTextBlock" Text="Source" Width="67" />
        <TextBox Height="20" Name="_sourceTextBox" Width="92" Text="{Binding Source, Mode=TwoWay}" />
    </StackPanel>
    <StackPanel HorizontalAlignment="Left" Name="stackPanel2" VerticalAlignment="Top" Width="165" Orientation="Horizontal">
        <TextBlock Height="20" Name="_destTextBlock" Text="Destination" Width="67" />
        <TextBox Height="20" Name="_destTextBox" Width="92" Text="{Binding Destination, Mode=OneWay}" IsReadOnly="True" />
    </StackPanel>
</StackPanel>

Anyway, if you’re building a non-trivial WPF application, I strongly recommend moving to the MVVM pattern, in the long-term your app will be much easier to maintain.