如何获取WPF DataGrid单元的位置？

Question

I have a DataGrid bound to a collection of Appointment objects. The grid shows appointments for a given week, with columns as days, and rows as times, ergo each cell is bound to an appointment.

When the user single clicks a cell, I want to show a small window with a summary of that cell's appointment. For reasons complex, I can't template the cell to show the summary, and more important, I want the summary to drop down and overlay the cells below the selected one.

In my command linked to the single-click, through some magic, I get the DataGridCellInfo for the selected cell itself, but that object offers no hint of any positioning, only some dimensions. The input binding for double-click looks like this:

<DataGrid.InputBindings>
    <!--TODO Remove name 'TheGrid' and find parent DataGrid-->
    <MouseBinding MouseAction="LeftDoubleClick"  Command="{Binding ApptClickCommand}" CommandParameter="{Binding ElementName=TheGrid, Path=SelectedCells}" />
</DataGrid.InputBindings>

and the command code receives a parameter of type SelectedCellsCollection , which contains only one DataGridCellInfo . I have no other information to work with in the command. As it is, I'm cheating quite a bit being so intimate with the view inside the viewmodel, so I'd like to avoid going overboard and using code-behind events directly.

Answer 1

A popup is something UI specific, and in my opinion should be positioned from the View somehow.

In the past when I did something similar , my ViewModel tracked the actual data, the SelectedItem, and a flag for IsDetailsVisible.

From the View, I would have a "popup" UserControl that sat on top of my grid. It's visibility was bound to the IsDetailsVisible property, and the data was bound to the SelectedItem . For my project, the popup was centered, however it should be an easy case to have the View set the Top/Left properties of the PopupUserControl so it matches the cell the user clicked on.

For finding the actual grid cell in the UI there's a few ways to go about that. The easiest would probably be to use the Click or MouseDown event, and from there position the PopupUserControl according to the Clicked DataGridCell. As I said, this kind of thing to me is view-specific, so should go in the code-behind the View.

Also, I never liked WPF's popup, so made my own custom UserControl that I would always use instead. The code can be found on my blog here if you're interested in using it or doing something similar.

Answer 2

Here is an example of how you could get the DataGridCell element and then find its screen coordinates using the Visual.PointToScreen method:

    private void AppClickCommandExecuted(IList<DataGridCellInfo> cells)
    {
        if(cells != null && cells.Count > 0)
        {
            DataGridCellInfo cellInfo = cells[0];
            FrameworkElement cellContent = cellInfo.Column.GetCellContent(cellInfo.Item);
            if (cellContent != null)
            {
                DataGridCell cell = cellContent.Parent as DataGridCell;
                if(cell != null)
                {
                    Point screenCoordinates = cell.PointToScreen(new Point(0, 0));
                    //place your popup based on the screen coordinates of the cell...
                }
            }
        }
    }