C# 中的右对齐组合框

Question

默认情况下，C# 组合框中的项目左对齐。 除了重写 DrawItem 方法和设置组合框绘制模式之外，是否有任何选项可用于更改此理由 --> DrawMode.OwnerDrawFixed？

干杯

Answer 1

如果您不介意另一侧的放置小部件，则可以将控件样式设置为 RightToLeft = RightToLeft.Yes。

或

设置 DrawMode = OwnerDrawFixed; 并挂钩 DrawItem 事件，
然后像

    private void comboBox1_DrawItem(object sender, DrawItemEventArgs e)
    {
        if (e.Index == -1)
            return;
        ComboBox combo = ((ComboBox) sender);
        using (SolidBrush brush = new SolidBrush(e.ForeColor))
        {
            e.DrawBackground();
            e.Graphics.DrawString(combo.Items[e.Index].ToString(), e.Font, brush, e.Bounds, new StringFormat(StringFormatFlags.DirectionRightToLeft));
            e.DrawFocusRectangle();
        }
    }

Answer 2

在 WPF 中，这就像指定 ItemContainerStyle 一样简单。在 Windows 窗体中，这有点棘手。如果没有自定义绘图，您可以在 ComboBox 上设置 RightToLeft 属性，但不幸的是，这也会影响下拉按钮。

由于 Windows 窗体使用本机 ComboBox，并且 Windows 没有类似 的 ComboBox 样式ES_RIGHT 会影响文本对齐，我认为您唯一的选择是诉诸所有者绘制。从 ComboBox 派生一个类并添加 TextAlignment 属性或其他内容可能是个好主意。然后，只有当 TextAlignment 居中或右对齐时，您才会应用绘图。

Answer 3

您必须“DrawMode = System.Windows.Forms.DrawMode.OwnerDrawFixed”并且
你自己的绘制方法是这样的。

protected virtual void OnDrawItem(object sender, DrawItemEventArgs e)
{
    var comboBox = sender as ComboBox;

    if (comboBox == null)
    {
        return;
    }

    e.DrawBackground();

    if (e.Index >= 0)
    {
        StringFormat sf = new StringFormat();
        sf.LineAlignment = StringAlignment.Center;
        sf.Alignment = StringAlignment.Center;

        Brush brush = new SolidBrush(comboBox.ForeColor);

        if ((e.State & DrawItemState.Selected) == DrawItemState.Selected)
        {
            brush = SystemBrushes.HighlightText;
        }

        e.Graphics.DrawString(comboBox.Items[e.Index].ToString(), comboBox.Font, brush, e.Bounds, sf);
    }
}

Answer 4

不幸的是，如果组合框设置为 DropDownList，则 OwnDrawItem 的方法似乎不起作用。然后人们会看到白色背景而不是预期的灰色。因此，我使用了 WPF 组合框，它看起来也与“正常”组合框不完全相同，但足够接近。

对我来说，实现两个属性、一种方法和一个通风口就足够了，如下所示：

    public partial class RightAlignedComboBox : ElementHost {

    public RightAlignedComboBox() {                   
        InitializeComponent();

        _comboBox = new() {
            HorizontalAlignment = HorizontalAlignment.Stretch,
            VerticalAlignment = VerticalAlignment.Stretch,
            HorizontalContentAlignment = HorizontalAlignment.Right,
            VerticalContentAlignment = VerticalAlignment.Center
        };

        _comboBox.SelectionChanged += comboBox_SelectionChanged;
        _comboBox.MouseWheel += comboBox_MouseWheel;

        this.Child = _comboBox;
    }

    #region Properties & Variables

    private ComboBox _comboBox;

    private IEnumerable<object> _items;

    /// <summary>
    /// Gets or sets the index specifying the currently selected item.
    /// </summary>      
    public int SelectedIndex {
        get {
            return _comboBox.SelectedIndex;
        }
        set {
            _comboBox.SelectedIndex = value;
        }
    }

    /// <summary>
    /// Gets or sets currently selected item in the combo box.
    /// </summary>      
    public object SelectedItem {
        get {
            return _items.ElementAt(_comboBox.SelectedIndex);
        }
        set {
            int selectedIndex = _items.IndexOfFirst(item => item.ToString() == value.ToString());
            _comboBox.SelectedIndex = selectedIndex;
        }
    }

    #endregion

    #region Methods

    /// <summary>
    /// Sets the items selectable in the combo box.
    /// </summary>
    /// <param name="items">The items to be put in the combo box.</param>
    public void SetItems(IEnumerable<object> items) {
        _items = items;

        _comboBox.Items.Clear();

        for (int i = 0; i < items.Count(); i++) {
            _comboBox.Items.Add(new ComboBoxItem() { Content = items.ElementAt(i).ToString() });
        }
    }

    #endregion

    #region Own events

    /// <summary>
    /// Event that is raised when the <see cref="SelectedIndex"/> changed either by clicking or by mouse wheel.
    /// </summary>
    public event EventHandler SelectionChangeCommitted = null;

    /// <summary>
    /// Raises the <see cref="SelectionChangeCommitted"/> event.
    /// </summary>
    private void onSelectionChangeCommitted() {
        SelectionChangeCommitted?.Invoke(this, EventArgs.Empty);
    }

    #endregion

    #region Events

    private void comboBox_MouseWheel(object sender, MouseWheelEventArgs e) {
        if (e.Delta < 0) {
            if (_comboBox.SelectedIndex != _comboBox.Items.Count - 1) {
                _comboBox.SelectedIndex++;
                onSelectionChangeCommitted();
            }
        }
        else {
            if (_comboBox.SelectedIndex != 0) {
                _comboBox.SelectedIndex--;
                onSelectionChangeCommitted();
            }
        }
    }

    private void comboBox_SelectionChanged(object sender, SelectionChangedEventArgs e) {
        if (_comboBox.IsFocused) {
            onSelectionChangeCommitted();
        }
    }

    #endregion
}