Binding Textbox to Two sources WPF - wpf

Question

I have a text box, which default value I want to bind to Combo box selecteItem, and same time I want my text box to be binded to Mvvm object property?
I checked here but the multibinding confuse me.
I would prefer to have xaml solution for this issue.
Addition:
In combobox I will select an Account, that account contain some values (Amount), I want to display Amount, But need my text box to be bounded to mvvm model object element stAmount. so the user can change the amount selected by combobbox and then this modified or unchanged amount value could be stored to text box binded model-object element (stAmount)

Answer 1

Making use of INotifyPropertyChanged:
XAML
<Window x:Class="INotifyPropertyChangedExample.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
DataContext="{Binding RelativeSource={RelativeSource Self}}"
Title="INotifyPropertyChanged Example" Width="380" Height="100">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="150" />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<Label Content="Account Name:" />
<Label Grid.Row="1" Grid.Column="0" Content="Account Balance:" />
<ComboBox Grid.Row="0" Grid.Column="1" Width="200" Height="25" ItemsSource="{Binding AccountsCollection}" SelectedItem="{Binding SelectedAccount}" DisplayMemberPath="Name" />
<TextBox Grid.Column="1" Grid.Row="1" Width="200" Height="25" Text="{Binding SelectedAccount.Balance}" />
</Grid>
</Window>
C#
namespace INotifyPropertyChangedExample
{
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Windows;
public partial class MainWindow : Window, INotifyPropertyChanged
{
private ObservableCollection<Account> acctountsCollection;
public ObservableCollection<Account> AccountsCollection
{
get
{
return this.acctountsCollection;
}
set
{
this.acctountsCollection = value;
OnPropertyChanged();
}
}
private Account selectedAccount;
public Account SelectedAccount
{
get
{
return this.selectedAccount;
}
set
{
this.selectedAccount = value;
OnPropertyChanged();
}
}
public MainWindow()
{
InitializeComponent();
this.AccountsCollection = new ObservableCollection<Account>()
{
new Account { Id = 1, Name = "My super account", Balance = 123.45 },
new Account { Id = 2, Name = "My super account 2", Balance = 543.21 },
};
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName = null)
{
var handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
public class Account
{
public int Id { get; set; }
public string Name { get; set; }
public double Balance { get; set; }
}
}
In this example we bind an ObservableCollection of Account objects to your ComboBox and keep track of which Account is selected through the SelectedItem property. We bind the TextBox text property to the Balance property of the selected Account object. Therefore when then selected Account object changes the value displayed in the TextBox changes to reflect the Balance of the Account.
Additionally if you change the value in the TextBox, the Balance value of the Account object is updated.

Answer 2

It seems to me like you want bind your textbox to the selected value property in your viewmodel not the combo box.
using System.Collections.ObjectModel;
using System.Windows;
namespace WpfApplication1
{
public partial class MainWindow : Window
{
public ObservableCollection<string> Items
{
get { return (ObservableCollection<string>)GetValue(ItemsProperty); }
set { SetValue(ItemsProperty, value); }
}
public static readonly DependencyProperty ItemsProperty =
DependencyProperty.Register("Items", typeof(ObservableCollection<string>), typeof(MainWindow), new PropertyMetadata(null));
public string SelectedValue
{
get { return (string)GetValue(SelectedValueProperty); }
set { SetValue(SelectedValueProperty, value); }
}
public static readonly DependencyProperty SelectedValueProperty =
DependencyProperty.Register("SelectedValue", typeof(string), typeof(MainWindow), new PropertyMetadata(null));
public MainWindow()
{
InitializeComponent();
Items = new ObservableCollection<string>();
Items.Add("Value 1");
Items.Add("Value 2");
Items.Add("Value 3");
Items.Add("Value 4");
Items.Add("Value 5");
Items.Add("Value 6");
}
}
}
and the xaml
<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
DataContext="{Binding RelativeSource={RelativeSource Self}}"
Title="MainWindow" Height="350" Width="525">
<Grid >
<Grid.RowDefinitions>
<RowDefinition/>
<RowDefinition/>
</Grid.RowDefinitions>
<ComboBox Grid.Row="0" ItemsSource="{Binding Items}" SelectedItem="{Binding SelectedValue}"/>
<TextBox Grid.Row="1" Text="{Binding SelectedValue}"/>
</Grid>
</Window>