Responding to object property changes within a class object hierarchy

Question

I am developing an application which uses a hierarchical object structure and displays a few key object properties from those objects on the main GUI within a DataGridView. Those values must update when the underlying data changes. I have considered a few options:

1. Bind the individual DataGridView cells to the relevant object properties. I understand that this is not possible, and DGV binding is all or nothing.
2. Dynamically position Textboxes over the grid cells and bind those, but this seems messy.
3. Create an intermediate list/array/collection which references only the relevant object properties, and then use that list as a data source for the DataGridView.
4. Respond to the PropertyChanged events. The complication is that I have got multiple classes. The top-level object exists within the UI scope, and has a child object which in turn may have multiple child objects of its own, and so on. The UI can access properties of all objects, but not their events.

I have been looking at passing the PropertyChanged event from whichever level it occurs up the chain so that it can be handled within the UI. So within a particular class I want to respond to OnPropertyChanged within that class, and within any children, and make any events raised available to the parent class. Thus events would flow up the tree to the top.

I understand how to do the two steps individually, I think, with reference to the following:

Handling OnPropertyChanged

Pass click event of child control to the parent control

However, although I presume the two can be combined, I am not quite sure how to do this. In the UI I have got this:

project.PropertyChanged += new PropertyChangedEventHandler(ProjectPropertyChanged);

private void ProjectPropertyChanged(object sender, PropertyChangedEventArgs e) {
    MessageBox.Show("In main UI. Project property changed!");
}

And then one level down I have got something like this:

public class Project : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    public Project() {
        childObject.PropertyChanged += new PropertyChangedEventHandler(ProjectPropertyChanged);
    }
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        var handler = PropertyChanged;
        if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
        ProjectPropertyChanged(sender, e); // this doesn't work due to different parameters
    }
    private void PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        // Event available to parent class
    }
}

The idea being that each class would pass its own OnPropertyChanged() events to its PropertyChanged() method, and respond to its children's OnPropertyChanged() events, and expose all to the parent class.

If doing this, ideally I would like to retain knowledge of which property changed in order to respond accordingly.

The most immediate issue is lack of compatibility between ProjectPropertyChanged and OnPropertyChanged due to different parameters. More fundamentally, though, I am not sure whether this method is workable or optimal.

How best to do this?

Answer 1

To answer my own question:

I tried unsuccessfully to do this with an intermediate binding source, using a DataTable (as per this question.). The problem was that I couldn't create references to the data objects. The DataTable seemed to contain values.

So I ended up using a method I was more sure about, but is less elegant, which is option 2 in my question above. I position Labels where I need bound data values, and bind to those labels. This works.

With some simplification, and pretending that our objects are animals, my solution was this:

Label[,] dashboardLabels = new Label[3,14];

private void Form1_Shown(object sender, EventArgs e)
{
  CreateLabels(); // create and position labels (no binding yet)
}

public void CreateLabels(int cols = 3, int rows = 14)
{

    for (int col = 0; col < cols; col++)
    {
        for (int row = 0; row < rows; row++)
        {
            // Create label...
            Label l = new Label();
            l.Text = "N/A";
            l.ForeColor = Color.Red
            dashboardLabels[col, row] = l;
            this.Controls.Add(l);

            // Position label over DGV cell...
            Point dgvCell = dataGridView1.GetCellDisplayRectangle(col + 2, rowNumbersLabel[row], false).Location;
            Point dgvGrid = dataGridView1.Location;
            l.Left = dgvGrid.X + dgvCell.X;
            l.Top = dgvGrid.Y + dgvCell.Y;

        }
    }
}
private void UpdateLabels(List<Dog> dogs)
{
    for (int i = 0; i < dogs; i++)
    {
        if (!dashboardLabels[i, 0].Visible) dashboardLabels[i, 0].Visible = true;
        if (dogs[i].IsSetUp) BindLabel(dashboardLabels[i, 0], dogs[i],"Name");
    }
}
private void BindLabel(Label l, Dog dog, string observation)
    {
        Binding b = new Binding("Text", dog, observation);
        l.DataBindings.Add(b);
        l.ForeColor = Color.Green;
    }
}

Then when the objects are created, I call UpdateLabels(). If not initialised, the label will show 'N/A' in red at this point. If initialised, the label will become green and will be bound to the object's name so it will update automatically from that point on.

I did much searching and the information I was finding suggested that a DataGridView does not support complex data binding i.e. it is pretty much one class to one DGV, or not at all. I couldn't find an alternative grid-like control which would do it either.