In WPF, how to display AdornerLayer on top of DataGrid

Question

I am using WPF datagrid from codeplex. I am using DatagridTemplateColumn and I have written datatemplates to display contents in each column.

Now I have to display some help message to a user when the any control in datagrid is focussed. For this I thought of using adorner layer. I used ComboBox loaded event and accessed the adrorner layer of it. I then added my own adorner layer with some thing to be displayed there similar to tooltip. Below is the code.

        TextBox txtBox = (TextBox)comboBox.Template.FindName("PART_EditableTextBox", comboBox);
        if (txtBox == null)
            return;

        txtBox.ToolTip = comboBox.ToolTip;
        AdornerLayer myAdornerLayer = AdornerLayer.GetAdornerLayer(txtBox);
        Binding bind = new Binding("IsKeyboardFocused");
        bind.Converter = new KeyToVisibilityConverter();
        bind.Source = txtBox;
        bind.Mode = BindingMode.OneWay;
        PEAdornerControl adorner = new PEAdornerControl(txtBox);
        adorner.SetBinding(PEAdornerControl.VisibilityProperty, bind);

PEAdorner layer is this ::

  public class PEAdornerControl : Adorner
  {
    Rect rect;

    // base class constructor.
    public PEAdornerControl(UIElement adornedElement)
        : base(adornedElement)
    { }

    protected override void OnRender(DrawingContext drawingContext)
    {
          .....
    }
  }

Now the problem is as follows. I am attaching screenshot of how it is looking in datagrid. If the datagrid has more than 4 rows, things are fine.Below is the screenshot

If the datagrid has less number of row, this adorner goes inside datagrid and is not visible to user. The screenshot is below

How do I get this adorner layer above the DataGrid? Please help me !!!

Answer 1

Just get the topmost AdornerLayer, instead

    static AdornerLayer GetAdornerLayer(FrameworkElement adornedElement)
    {
        var w = Window.GetWindow(adornedElement);
        var vis = w.Content as Visual;

        return AdornerLayer.GetAdornerLayer(vis);
    }

Also, if you have the name of your DataGrid you can get the nearest layer above it:

AdornerLayer myAdornerLayer = AdornerLayer.GetAdornerLayer(myDataGrid);

Answer 2

I looked at your question again and i think this is what you would need.

    TextBox txtBox = (TextBox)comboBox.Template.FindName("PART_EditableTextBox", comboBox);
    if (txtBox == null)
        return;

    txtBox.ToolTip = comboBox.ToolTip;

    //this is locating the DataGrid that contains the textbox
    DataGrid parent = FindParent<DataGrid>(this);

    //Get the adorner for the parent
    AdornerLayer myAdornerLayer = AdornerLayer.GetAdornerLayer(parent);
    Binding bind = new Binding("IsKeyboardFocused");
    bind.Converter = new KeyToVisibilityConverter();
    bind.Source = txtBox;
    bind.Mode = BindingMode.OneWay;
    PEAdornerControl adorner = new PEAdornerControl(txtBox);
    adorner.SetBinding(PEAdornerControl.VisibilityProperty, bind);

The find parent method is this:

public T FindParent<T>(DependencyObject obj) where T : DepedencyObject
{
  if (obj == null)
     return null;
  DependencyOBject parent = VisualTreeHelper.GetParent(obj);

  if (parent is T)
      return parent as T;
  else
      return FindParent<T>(parent);
 }

You may need to set the position of your adorner in the OnRender method but this should work. One thing to consider though is that if your DataGrid is within another container (such as a panel, grid, etc) then you may still run into your clipping problem.

The clipping problem is due to the fact that when a container checks the layout of its children it does not normally take into account their adorners. To combat this you would possibly need to create your own control and override the MeasuerOverride(Size constraint) method.

Example:

public class MyPanel : Panel
{
   protected override Size MeasureOverride(Size constraint)
   {
     Size toReturn = new Size();
     foreach (UIElement child in this.InternalChildren)
     {
       //Do normal Measuring of children

       foreach( UIElement achild in AdornerLayer.GetAdorners(child))
       //Measure child adorners and add to return size as needed
     }

     return toReturn;
   }
 }

That code is really rough for measure but should point you in the right direction. Look at the documentation page http://msdn.microsoft.com/en-us/library/system.windows.frameworkelement.measureoverride.aspx for information about measuring child elements in a panel.