Difference between Window.DataContext and Window.Resources

Question

Hello,

Can someone tell me what the difference is and when to take what?

Answer 1

Hi Markus,
iit's easy to bind SelectedItem an in Setter call your Processing. Try this demo:

<Window x:Class="WpfApp1.Window72"  
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
        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:local="clr-namespace:WpfApp72"  
        mc:Ignorable="d"  
        Title="Window72" Height="450" Width="800">  
  <Window.DataContext>  
    <local:ViewModel/>  
  </Window.DataContext>  
    <Grid>  
    <ComboBox Height="20" Width="100"  
              ItemsSource="{Binding ComList}"  
              DisplayMemberPath="CmbValue"  
              SelectedItem="{Binding SelectedCom}"/>  
  </Grid>  
</Window>  

And classes:

Answer 2

FrameworkElement.DataContext property gets or sets the data context for an element when it participates in data binding.FrameworkElement.Resources Property gets or sets the locally-defined resource dictionary. They are both can set the datacontext for the FrameworkElement. If you use the Resources to host the data soruce, you need to set the DataContext for the element. In this demo, you can use it like below:

 <Window.Resources>  
        <local:ViewModel x:Key="MyData"></local:ViewModel>  
    </Window.Resources>  
    <Grid>  
        <ComboBox Name="cbStatus"  
                  DataContext ="{StaticResource MyData}"   
                  ItemsSource="{Binding Comlist}"  
                  SelectedItem="{Binding Comlist[4]}"  
                  SelectedValuePath="CmbValue"       
                  DisplayMemberPath="CmbText"     
                  Width="100" Height="30"                 
                  SelectionChanged="cbStatus_SelectionChanged"  
                  />  
        
    </Grid>  

Answer 3

OK, I understood the difference.

1- UserInterface
2- ViewModel, I use this

 public class RelayCommand : ICommand  
    {  
        private readonly Predicate<object> _canExecute;  
        private readonly Action<object> _action;  
        public RelayCommand(Action<object> action) { _action = action; _canExecute = null; }  
        public RelayCommand(Action<object> action, Predicate<object> canExecute) { _action = action; _canExecute = canExecute; }  
        public void Execute(object o) => _action(o);  
        public bool CanExecute(object o) => _canExecute == null ? true : _canExecute(o);  
        public event EventHandler CanExecuteChanged  
        {  
            add { CommandManager.RequerySuggested += value; }  
            remove { CommandManager.RequerySuggested -= value; }  
        }  

3-Model, here my special combo box
4 - MainWindow according to my research, there shouldn't be any code.