C# – WPF Binding DataTable column to a textbox

cdata-bindingdatatabletextboxwpf

I'm getting started with WPF and finding it difficult to get even the most simple binding working. Here's some givens…

I have an object that queries an existing database and returns a "datatable" object, the data comes back (and for test purposes, only a single row and single column called "MyTextColumn")

The data table is not "Strongly typed" as I've read in other places trying to force the issue of strongly typed objects. I want to understand the underlying mechanisms from the code-behind perspective, AND not from the XAML perspective. From reading, apparently you can't bind directly to a data table, but you can to the "DefaultView" of a DataTable object (makes no sense to me since they point to same record (or set of records, with exception of say a filter of some type).

So, in the XAML portion of the window,

<src:MyWindow blah, blah >
  <Grid Name="grdTesting">
    <Grid.RowDefinitions>
      <RowDefinition />
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
      <ColumnDefinition />
      <ColumnDefinition />
    </Grid.ColumnDefinitions>

    <Label Name="lblMyTextColumn" 
        Content="Just the label" 
        Grid.Row="0" Grid.Column="0 "/>

    <TextBox Name="txtMyTextColumn"
        Grid.Row="0" Grid.Column="1"
        Width="120" />
  </Grid>
</src:MyWindow>

So now, I'm in the code-behind, what I've read is you have to have a BindingListCollectionView oView;

public partial class MyWindow : Window
{
  BindingListCollectionView oView;
  MyQueryingManager oTestMgr;

  public MyWindow()
  {
    InitializeComponent();

    oTestMgr = new MyQueryingManager();
    DataTable oResults = oTestMgr.GetTheData();

    // Data context for the form bound to the Table retrieved
    oView = new BindingListCollectionView( oResults.DefaultView );

    // One place said the Window should get the binding context
    DataContext = oView;

    // another indicated the grid...  Just need to know which I SHOULD be using
    grdTesting.DataContext = oView;


    // Now, for my binding preparation...
    Binding bindMyColumn = new Binding();
    bindMyColumn.Source = oView;
    bindMyColumn.Path = new PropertyPath("MyTextColumn");
    txtMyTextColumn.SetBinding( TextBox.TextProperty, bindMyColumn );
  }
}

So… what am I missing here… Should be simple, nothing complex, I have a data table, with a record, that has a value. Run the form (no matter binding context to the Window or the Grid), and the record value does not show in the textbox control. Once I understand the behavior on a single textbox, I can go on with all the other elements (validation, input mask, formatting, etc), but am stuck right at the gate on this one.

Thanks

Best Answer

First, you can bind to a DataTable but you can also use the default view (which is a DataView) etc.

Usually, you bind a DataTable to an ItemsControl or a control that derives from it, such as ListBox, DataGrid etc. Then each container will get a DataRow (or DataRowView) and the binding will be easy.

Since you are binding it directly to a TextBox inside a Grid you would have to specify both Row and Column in the binding. The correct path to bind to the column named "MyTextColumn" in the first row is Rows[0][MyTextColumn]

Try this

Binding bindMyColumn = new Binding();
bindMyColumn.Source = oResults;
bindMyColumn.Path = new PropertyPath("Rows[0][MyTextColumn]");
txtMyTextColumn.SetBinding(TextBox.TextProperty, bindMyColumn);

A problem if you're binding directly to the DataTable is that it doesn't implement INotifyPropertyChanged so the UI won't know that the value has changed if it is changed from some other source. In this case, you can use a DataView instead. The binding syntax will be a little different here since you access the DataRowViews directly with the index operator.

dataView = oResults.DefaultView;
// Now, for my binding preparation...
Binding bindMyColumn = new Binding();
bindMyColumn.Source = dataView;
bindMyColumn.Path = new PropertyPath("[0][MyTextColumn]");
txtMyTextColumn.SetBinding(TextBox.TextProperty, bindMyColumn);

Related Solutions

C# – LINQ query on a DataTable

You can't query against the DataTable's Rows collection, since DataRowCollection doesn't implement IEnumerable<T>. You need to use the AsEnumerable() extension for DataTable. Like so:

var results = from myRow in myDataTable.AsEnumerable()
where myRow.Field<int>("RowNo") == 1
select myRow;

And as @Keith says, you'll need to add a reference to System.Data.DataSetExtensions

AsEnumerable() returns IEnumerable<DataRow>. If you need to convert IEnumerable<DataRow> to a DataTable, use the CopyToDataTable() extension.

Below is query with Lambda Expression,

var result = myDataTable
    .AsEnumerable()
    .Where(myRow => myRow.Field<int>("RowNo") == 1);

C# – Binding a WPF ComboBox to a custom list

You set the DisplayMemberPath and the SelectedValuePath to "Name", so I assume that you have a class PhoneBookEntry with a public property Name.

Have you set the DataContext to your ConnectionViewModel object?

I copied you code and made some minor modifications, and it seems to work fine. I can set the viewmodels PhoneBookEnty property and the selected item in the combobox changes, and I can change the selected item in the combobox and the view models PhoneBookEntry property is set correctly.

Here is my XAML content:

<Window x:Class="WpfApplication6.Window1"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Window1" Height="300" Width="300">
<Grid>
    <StackPanel>
        <Button Click="Button_Click">asdf</Button>
        <ComboBox ItemsSource="{Binding Path=PhonebookEntries}"
                  DisplayMemberPath="Name"
                  SelectedValuePath="Name"
                  SelectedValue="{Binding Path=PhonebookEntry}" />
    </StackPanel>
</Grid>
</Window>

And here is my code-behind:

namespace WpfApplication6
{

    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
            ConnectionViewModel vm = new ConnectionViewModel();
            DataContext = vm;
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            ((ConnectionViewModel)DataContext).PhonebookEntry = "test";
        }
    }

    public class PhoneBookEntry
    {
        public string Name { get; set; }

        public PhoneBookEntry(string name)
        {
            Name = name;
        }

        public override string ToString()
        {
            return Name;
        }
    }

    public class ConnectionViewModel : INotifyPropertyChanged
    {
        public ConnectionViewModel()
        {
            IList<PhoneBookEntry> list = new List<PhoneBookEntry>();
            list.Add(new PhoneBookEntry("test"));
            list.Add(new PhoneBookEntry("test2"));
            _phonebookEntries = new CollectionView(list);
        }

        private readonly CollectionView _phonebookEntries;
        private string _phonebookEntry;

        public CollectionView PhonebookEntries
        {
            get { return _phonebookEntries; }
        }

        public string PhonebookEntry
        {
            get { return _phonebookEntry; }
            set
            {
                if (_phonebookEntry == value) return;
                _phonebookEntry = value;
                OnPropertyChanged("PhonebookEntry");
            }
        }

        private void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
        public event PropertyChangedEventHandler PropertyChanged;
    }
}

Edit: Geoffs second example does not seem to work, which seems a bit odd to me. If I change the PhonebookEntries property on the ConnectionViewModel to be of type ReadOnlyCollection, the TwoWay binding of the SelectedValue property on the combobox works fine.

Maybe there is an issue with the CollectionView? I noticed a warning in the output console:

System.Windows.Data Warning: 50 : Using CollectionView directly is not fully supported. The basic features work, although with some inefficiencies, but advanced features may encounter known bugs. Consider using a derived class to avoid these problems.

Edit2 (.NET 4.5): The content of the DropDownList can be based on ToString() and not of DisplayMemberPath, while DisplayMemberPath specifies the member for the selected and displayed item only.

Best Answer

Related Solutions

C# – LINQ query on a DataTable

C# – Binding a WPF ComboBox to a custom list

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