Changing the Color of ComboBox highlighting

问题

I am trying to work around changing the color of highlighting in a ComboBox dropdown on a C# Windows Forms application. I have searched the whole web for an answer, and the best option i found so far was to draw a rectangle of the desired color when the item that is selected is being drawn.

Class Search
{
    Public Search()
    {
    }

    private void addFilter()
    {
        ComboBox field = new ComboBox();

        field.Items.AddRange(new string[] { "Item1", "item2" });
        field.Text = "Item1";
        field.DropDownStyle = ComboBoxStyle.DropDownList;
        field.FlatStyle = FlatStyle.Flat;
        field.BackColor = Color.FromArgb(235, 235, 235);
        field.DrawMode = DrawMode.OwnerDrawFixed;
        field.DrawItem += field_DrawItem;
    }

    private void field_DrawItem(object sender, DrawItemEventArgs e)
    {
        if (e.Index >= 0)
        {
            ComboBox combo = sender as ComboBox;

            if (e.Index == combo.SelectedIndex)
                e.Graphics.FillRectangle(new SolidBrush(Color.Gray),
                                         e.Bounds
                                        );
            else
                e.Graphics.FillRectangle(new SolidBrush(combo.BackColor),
                                         e.Bounds
                                        );

            e.Graphics.DrawString(combo.Items[e.Index].ToString(), e.Font,
                                  new SolidBrush(combo.ForeColor),
                                  new Point(e.Bounds.X, e.Bounds.Y)
                                 );
        }
    }
}

The problem with this code, is that once another Item in the dropdown is selected, the other Item I draw a rectangle is still with the color i want to highlight. Then i tried to save the last Item drawn and redraw it:

Class Search
{
    private DrawItemEventArgs lastDrawn;

    Public Search()
    {
        lastDrawn = null;
    }

    private void addFilter()
    {
        ComboBox field = new ComboBox();

        field.Items.AddRange(new string[] { "Item1", "item2" });
        field.Text = "Item1";
        field.DropDownStyle = ComboBoxStyle.DropDownList;
        field.FlatStyle = FlatStyle.Flat;
        field.BackColor = Color.FromArgb(235, 235, 235);
        field.DrawMode = DrawMode.OwnerDrawFixed;
        field.DrawItem += field_DrawItem;
    }

    private void field_DrawItem(object sender, DrawItemEventArgs e)
    {
        if (e.Index >= 0)
        {
            ComboBox combo = sender as ComboBox;
            if (e.Index == combo.SelectedIndex)
            {
                e.Graphics.FillRectangle(new SolidBrush(Color.Gray), e.Bounds);
                if(lastDrawn != null)
                    lastDrawn.Graphics.FillRectangle(new SolidBrush(combo.BackColor),
                                                 lastDrawn.Bounds
                                                );
                lastDrawn = e;
            }
            else
                e.Graphics.FillRectangle(new SolidBrush(combo.BackColor),
                                         e.Bounds
                                        );

            e.Graphics.DrawString(combo.Items[e.Index].ToString(), e.Font,
                                  new SolidBrush(combo.ForeColor),
                                  new Point(e.Bounds.X, e.Bounds.Y)
                                 );
        }
    }
}

This line returns an error because of lastDrawn.Bounds (incompatible type)

lastDrawn.Graphics.FillRectangle(new SolidBrush(combo.BackColor),
                                                 lastDrawn.Bounds
                                                );

I am feeling that changing the highlight color of the dropdown is impossible. Thanks in advance!

回答1:

In case you are using the ComboBox in more than one place in your project, it will not make sense to repeat the same code for DrawItem event over and over again. Just add this class to your project and you will have a new ComboBox control that has the HightlightColor property which will makes it easier to use the control all over the project:

class AdvancedComboBox : ComboBox
{
    new public System.Windows.Forms.DrawMode DrawMode { get; set; }
    public Color HighlightColor { get; set; }

    public AdvancedComboBox()
    {
        base.DrawMode = System.Windows.Forms.DrawMode.OwnerDrawFixed;
        this.HighlightColor = Color.Gray;
        this.DrawItem += new DrawItemEventHandler(AdvancedComboBox_DrawItem);
    }

    void AdvancedComboBox_DrawItem(object sender, DrawItemEventArgs e)
    {
        if (e.Index < 0)
            return;

        ComboBox combo = sender as ComboBox;
        if ((e.State & DrawItemState.Selected) == DrawItemState.Selected)
            e.Graphics.FillRectangle(new SolidBrush(HighlightColor),
                                     e.Bounds);
        else
            e.Graphics.FillRectangle(new SolidBrush(combo.BackColor),
                                     e.Bounds);

        e.Graphics.DrawString(combo.Items[e.Index].ToString(), e.Font,
                              new SolidBrush(combo.ForeColor),
                              new Point(e.Bounds.X, e.Bounds.Y));

        e.DrawFocusRectangle();
    }
}

来源：https://stackoverflow.com/questions/13212179/changing-the-color-of-combobox-highlighting

标签

winforms

combobox

highlighting