How to create a comparable Image

问题:

I have a DataGridView which has been bound to a generic BindingList. I want to be able to apply sort and search on columns of type DataGridViewImageColumn. The basic idea is to store a name into the image Tag and use is for sorting and searching. How can I do that?

It seems several ways to do it:

1. Creating a new class inheriting System.Drawing.Image and making it comparable.
   • Image is an abstract class and if I inherit from it (as well as IComparable interface), I'll encounter with this error message: The type 'System.Drawing.Image' has no constructors defined. What's the problem here? Image is an abstract not a sealed class, but it doesn't allow me to inherit it!

2. Using protected override ApplySortCore method of inherited class from BindingList<T>.

   • This method is like so:

     class MyBindingList<T> : BindingList<T>
     {
         ...
         protected override void ApplySortCore(PropertyDescriptor prop,
                                               ListSortDirection direction)
         {
             if (prop.PropertyType.Equals(typeof(Image)))
             {
                 /* I have no idea! */
             }
         }
     }
     

3. Creating a new DataGridViewColumn inheriting from DataGridViewImageColumn.
   • This doesn't seem to be easy and may be used if other ideas are unusable.

Thanks in advance

回答1:

Create a class (X) that incapsulates System.Drawing. Image + ImageAlias string property. Bind your image column to X.Image and search over X.ImageAlias.

Sorry but don't have a coding tool on my hands to provide an example, but this is a basic idea.

Hope this helps.

回答2:

I found the way!

---

MyBindingList

class MyBindingList<T> : BindingList<T>
{
    ...
    protected override void ApplySortCore(PropertyDescriptor prop,
                                          ListSortDirection direction)
    {
        if (prop.PropertyType.Equals(typeof(Image)))
        {
            _SortPropertyCore = prop;
            _SortDirectionCore = direction;

            var items = this.Items;
            Func<T, object> func =
                new Func<T, object>(t => (prop.GetValue(t) as Image).Tag);

            switch (direction)
            {
                case ListSortDirection.Ascending:
                    items = items.OrderBy(func).ToList();
                    break;

                case ListSortDirection.Descending:
                    items = items.OrderByDescending(func).ToList();
                    break;
            }

            ResetItems(items as List<T>);
            ResetBindings();
        }
        else
        {
            ...
        }
    }

    private void ResetItems(List<T> items)
    {
        base.ClearItems();

        for (int itemIndex = 0; itemIndex < items.Count; itemIndex++)
        {
            base.InsertItem(itemIndex, items[itemIndex]);
        }
    }
}

---

MyDataObject

class MyDataObject : INotifyPropertyChanged
{
    ...

    public Image MyProp
    {
        get
        {
            return CreateComparableImage(myImage, "myImage");
        }
    }

    private Image CreateComparableImage(Image image, string alias)
    {
        Image taggedImage = new Bitmap(image);
        taggedImage.Tag = alias;

        return taggedImage;
    }
}

---

Form

class MyForm : Form
{
    ...

    void BindDGV()
    {
        dataGridView1.Columns["myColumnName"].DataPropertyName = "MyProp";
        dataGridView1.DataSource = MyBindingList<MyDataObject>(...);
    }
}