Setting DataContext in XAML in WPF

Question

I have following code   MainWindow xaml   lt Window x Class  SampleApplication 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          DataContext   Binding Employee   gt       lt Grid gt                  lt Grid RowDefinitions gt               lt RowDefinition Height  Auto    gt               lt RowDefinition Height  Auto    gt           lt  Grid RowDefinitions gt           lt Grid ColumnDefinitions gt               lt ColumnDefinition Width  Auto    gt               lt ColumnDefinition Width  200    gt           lt  Grid ColumnDefinitions gt            lt Label Grid Row  0  Grid Column  0  Content  ID    gt           lt Label Grid Row  1  Grid Column  0  Content  Name    gt           lt TextBox Grid Column  1  Grid Row  0  Margin  3  Text   Binding EmpID     gt           lt TextBox Grid Column  1  Grid Row  1  Margin  3  Text   Binding EmpName     gt        lt  Grid gt   lt  Window gt    Employee cs  namespace SampleApplication       public class Employee               public Employee                         EmployeeDetails employeeDetails   new EmployeeDetails                employeeDetails EmpID   123              employeeDetails EmpName    ABC                        public class EmployeeDetails               private int empID          public int EmpID                       get                               return empID                            set                               empID   value                                   private string empName          public string EmpName                       get                               return empName                            set                               empName   value                                    This is very simple code and I just want to bind the EmpID and EmpName properties in my Employee cs class to Text properties of Textboxes in MainWindow xaml but nothing is appearing in my these textboxes when I am running the code  Is the binding right

User · Answer

First of all you should create property with employee details in the Employee class:

public class Employee
{
    public Employee()
    {
        EmployeeDetails = new EmployeeDetails();
        EmployeeDetails.EmpID = 123;
        EmployeeDetails.EmpName = "ABC";
    }

    public EmployeeDetails EmployeeDetails { get; set; }
}

If you don't do that, you will create instance of object in Employee constructor and you lose reference to it.

In the XAML you should create instance of Employee class, and after that you can assign it to DataContext.

Your XAML should look like this:

<Window x:Class="SampleApplication.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"
    xmlns:local="clr-namespace:SampleApplication"
   >
    <Window.Resources>
        <local:Employee x:Key="Employee" />
    </Window.Resources>
    <Grid DataContext="{StaticResource Employee}">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto" />
            <ColumnDefinition Width="200" />
        </Grid.ColumnDefinitions>

        <Label Grid.Row="0" Grid.Column="0" Content="ID:"/>
        <Label Grid.Row="1" Grid.Column="0" Content="Name:"/>
        <TextBox Grid.Column="1" Grid.Row="0" Margin="3" Text="{Binding EmployeeDetails.EmpID}" />
        <TextBox Grid.Column="1" Grid.Row="1" Margin="3" Text="{Binding EmployeeDetails.EmpName}" />
    </Grid>
</Window>

Now, after you created property with employee details you should binding by using this property:

Text="{Binding EmployeeDetails.EmpID}"

User · Answer

There are several issues here    You can t assign DataContext as DataContext   Binding Employee   because it s a complex object which can t be assigned as string  So you have to use  lt Window DataContext gt  lt  Window DataContext gt  syntax  You assign the class that represents the data context object to the view  not an individual property so  Binding Employee  is invalid here  you just have to specify an object  Now when you assign data context using valid syntax like below        lt Window DataContext gt         lt local Employee  gt      lt  Window DataContext gt     know that you are creating a new instance of the Employee class and assigning it as the data context object  You may well have nothing in default constructor so nothing will show up  But then how do you manage it in code behind file  You have typecast the DataContext       private void my button Click object sender  RoutedEventArgs e                Employee e    Employee  DataContext           A second way is to assign the data context in the code behind file itself  The advantage then is your code behind file already knows it and can work with it   public partial class MainWindow   Window      Employee employee   new Employee        public MainWindow               InitializeComponent            DataContext   employee

User · Answer

This code will always fail   As written  it says   Look for a property named  Employee  on my DataContext property  and set it to the DataContext property   Clearly that isn t right   To get your code to work  as is  change your window declaration to    lt Window x Class  SampleApplication MainWindow      xmlns  http   schemas microsoft com winfx 2006 xaml presentation      xmlns x  http   schemas microsoft com winfx 2006 xaml      xmlns local  clr-namespace SampleApplication      Title  MainWindow  Height  350  Width  525  gt   lt Window DataContext gt      lt local Employee  gt   lt  Window DataContext gt    This declares a new XAML namespace  local  and sets the DataContext to an instance of the Employee class  This will cause your bindings to display the default data  from your constructor    However  it is highly unlikely this is actually what you want  Instead  you should have a new class  call it MainViewModel  with an Employee property that you then bind to  like this   public class MainViewModel      public Employee MyEmployee   get  set      In reality this should utilize INotifyPropertyChanged      Now your XAML becomes    lt Window x Class  SampleApplication MainWindow          xmlns  http   schemas microsoft com winfx 2006 xaml presentation          xmlns x  http   schemas microsoft com winfx 2006 xaml          xmlns local  clr-namespace SampleApplication          Title  MainWindow  Height  350  Width  525  gt       lt Window DataContext gt          lt local MainViewModel  gt       lt  Window DataContext gt               lt TextBox Grid Column  1  Grid Row  0  Margin  3  Text   Binding MyEmployee EmpID     gt       lt TextBox Grid Column  1  Grid Row  1  Margin  3  Text   Binding MyEmployee EmpName     gt    Now you can add other properties  of other types  names   etc  For more information  see Implementing the Model-View-ViewModel Pattern

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