自定义 C# 按钮的 DialogResult 在模态表单上无法正常工作

Question

在制作 Winforms ImageButton 类 (C#) 时遇到了一点麻烦。我的 ImageButton 类实现了 IButtonControl 接口，但是当我将它添加到表单并将按钮的 DialogResult 设置为 'OK' ，然后在表单上调用 ShowDialog() 时，按下按钮不会关闭表单并返回 DialogResult，如正常的 Winforms Button 控件。

这是我对 ImageButton 的实现，你可以随意使用它。

/// <summary>
/// A control that displays an image and responds to mouse clicks on the image.
/// </summary>
[PermissionSet(SecurityAction.Demand, Name = "FullTrust")]
[Designer(typeof(ImageButtonDesigner))]
[ToolboxItem(typeof(ImageButtonToolboxItem))]
public class ImageButton : PictureBox, IButtonControl, INotifyPropertyChanged
{
    #region Constructors

    /// <summary>
    /// Initializes a new instance of the ImageButton class using the default initial values.
    /// </summary>
    public ImageButton()
    {
        DoubleBuffered = true;
        BackColor = Color.Transparent;
        SizeMode = PictureBoxSizeMode.AutoSize;
    }

    #endregion

    #region Properties

    /// <summary>
    /// Backing field for the DialogResult property.
    /// </summary>
    private DialogResult dialogResult;

    /// <summary>
    /// Gets or sets a value that is returned to the parent form when the button is clicked.
    /// </summary>
    [Category("Behavior")]
    [Description("The dialog-box result produced in a modal form by clicking the button")]
    public DialogResult DialogResult
    {
        get
        {
            return dialogResult;
        }

        set
        {
            if (Enum.IsDefined(typeof(DialogResult), value))
                dialogResult = value;
            else
                throw new InvalidEnumArgumentException("value", (int)value, typeof(DialogResult));
        }
    }

    /// <summary>
    /// Backing field for the Idle property.
    /// </summary>
    private Image idle;

    /// <summary>
    /// The image that will be displayed on the control when the mouse is not over a visible part of it.
    /// </summary>
    [Category("Appearance")]
    [Description("The image that will be displayed on the Control when the mouse is not over a visible part of it.")]
    public Image Idle
    {
        get
        {
            return idle;
        }

        set
        {
            idle = value;

            NotifyPropertyChanged();
        }
    }

    /// <summary>
    /// Backing field for the Mouseover property
    /// </summary>
    private Image mouseover;

    /// <summary>
    /// The image that will be displayed on the control when the mouse is over a visible part of it.
    /// </summary>
    [Category("Appearance")]
    [Description("The image that will be displayed on the control when the mouse is over a visible part of it.")]
    public Image Mouseover
    {
        get { return mouseover; }

        set
        {
            mouseover = value;

            NotifyPropertyChanged();
        }
    }

    /// <summary>
    /// Backing field for the Mousedown property
    /// </summary>
    private Image mousedown;

    /// <summary>
    /// The image that will be displayed on the control when the left mouse button is held down and the mouse is over a visible part of it.
    /// </summary>
    [Category("Appearance")]
    [Description("The image that will be displayed on the control when the left mouse button is held down and the mouse is over a visible part of it.")]
    public Image Mousedown
    {
        get { return mousedown; }

        set
        {
            mousedown = value;

            NotifyPropertyChanged();
        }
    }

    /// <summary>
    /// Gets or sets the text associated with the control.
    /// </summary>
    [Browsable(true)]
    [DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)]
    [Category("Appearance")]
    [Description("The text associated with the control.")]
    public override string Text
    {
        get
        {
            return base.Text;
        }
        set
        {
            base.Text = value;
        }
    }

    /// <summary>
    /// Gets or sets the font of the text displayed by the control.
    /// </summary>
    [Browsable(true)]
    [DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)]
    [Category("Appearance")]
    [Description("The font used to display text in the control.")]
    public override Font Font
    {
        get
        {
            return base.Font;
        }
        set
        {
            base.Font = value;
        }
    }

    /// <summary>
    /// Gets or sets the image that is displayed by the PictureBox.
    /// </summary>
    [EditorBrowsable(EditorBrowsableState.Never)]
    [Browsable(false)]
    [Category("Appearance")]
    [Description("The image displayed in the PictureBox.")]
    new public Image Image
    {
        get
        {
            return base.Image;
        }

        set
        {
            base.Image = value;
        }
    }

    /// <summary>
    /// Backing field for the ButtonState property.
    /// </summary>
    private ButtonStates buttonState = ButtonStates.None;

    /// <summary>
    /// The current state of the button.
    /// </summary>
    private ButtonStates ButtonState
    {
        get { return buttonState; }

        set
        {
            buttonState = value;

            NotifyPropertyChanged();
        }
    }

    /// <summary>
    /// Gets the default size of the control.
    /// </summary>
    protected override Size DefaultSize
    {
        get
        {
            return new Size(75, 23);
        }
    }

    #endregion

    #region Enums

    /// <summary>
    /// Specifies the current state of a button.
    /// </summary>
    [Flags]
    private enum ButtonStates : byte
    {
        /// <summary>
        /// 
        /// </summary>
        [Description("")]
        None = 0,

        /// <summary>
        /// 
        /// </summary>
        [Description("")]
        Default = 1 << 0,

        /// <summary>
        /// 
        /// </summary>
        [Description("")]
        Mouseover = 1 << 1,

        /// <summary>
        /// 
        /// </summary>
        [Description("")]
        Mousedown = 1 << 2
    }

    #endregion

    #region Events

    /// <summary>
    /// Occurs when a property value changes.
    /// </summary>
    [Category("Property Changed")]
    [Description("Occurs when a property value changes.")]
    public event PropertyChangedEventHandler PropertyChanged;

    #endregion

    #region Methods

    /// <summary>
    /// Raises the System.ComponentModel.PropertyChanged event.
    /// </summary>
    /// <param name="propertyName">the name of the property that changed.</param>
    protected virtual void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }

        if (propertyName == "Idle")
            Image = Idle;
    }

    /// <summary>
    /// Notifies the button whether it is the default button so that it can adjust its appearance accordingly.
    /// </summary>
    /// <param name="value">true if the button is to have the appearance of the default button; otherwise, false.</param>
    public void NotifyDefault(bool value)
    {
        ButtonState = value ? ButtonState | ButtonStates.Default : ButtonState & ~ButtonStates.Default;
    }

    /// <summary>
    /// Generates a Click event for a button.
    /// </summary>
    public void PerformClick()
    {
        if (CanSelect)
        {
            OnClick(EventArgs.Empty);
        }
    }

    /// <summary>
    /// Raises the System.Windows.Control.TextChanged event.
    /// </summary>
    /// <param name="e">A System.EventArgs that contains the event data.</param>
    protected override void OnTextChanged(EventArgs e)
    {
        base.OnTextChanged(e);

        Refresh();
    }

    /// <summary>
    /// Raises the System.Windows.Forms.Paint event.
    /// </summary>
    /// <param name="pe">A PaintEventArgs that contains the event data.</param>
    protected override void OnPaint(PaintEventArgs pe)
    {
        base.OnPaint(pe);

        if ((!string.IsNullOrEmpty(Text)) && (pe != null) && (base.Font != null))
        {
            SolidBrush drawBrush = new SolidBrush(base.ForeColor);

            // Calculate the size of the text that will be drawn onto the control.
            SizeF drawStringSize = pe.Graphics.MeasureString(base.Text, base.Font);

            // The registration point used to draw the text.
            PointF drawPoint;

            if (base.Image != null)
                drawPoint = new PointF(base.Image.Width / 2 - drawStringSize.Width / 2, base.Image.Height / 2 - drawStringSize.Height / 2);
            else
                drawPoint = new PointF(base.Width / 2 - drawStringSize.Width / 2, base.Height / 2 - drawStringSize.Height / 2);

            pe.Graphics.DrawString(base.Text, base.Font, drawBrush, drawPoint);
        }
    }

    /// <summary>
    /// Raises the System.Windows.Forms.MouseEnter event.
    /// </summary>
    /// <param name="e">A System.EventArgs that contains the event data.</param>
    protected override void OnMouseEnter(EventArgs e)
    {
        base.OnMouseEnter(e);

        ButtonState |= ButtonStates.Mouseover;
        Image = Mouseover;
    }

    /// <summary>
    /// Raises the System.Windows.Forms.MouseLeave event.
    /// </summary>
    /// <param name="e">A System.EventArgs that contains the event data.</param>
    protected override void OnMouseLeave(EventArgs e)
    {
        base.OnMouseLeave(e);

        ButtonState &= ~ButtonStates.Mouseover;
        Image = Idle;
    }

    /// <summary>
    /// Raises the System.Windows.Forms.MouseDown event.
    /// </summary>
    /// <param name="e">A System.Windows.Forms.MouseEventArgs that contains the event data.</param>
    protected override void OnMouseDown(MouseEventArgs e)
    {
        base.OnMouseDown(e);

        ButtonState |= ButtonStates.Mousedown;
        Image = Mousedown;
    }

    /// <summary>
    /// Raises the System.Windows.Forms.MouseUp event.
    /// </summary>
    /// <param name="e">A System.Windows.Forms.MouseEventArgs that contains the event data.</param>
    protected override void OnMouseUp(MouseEventArgs e)
    {
        base.OnMouseUp(e);

        ButtonState &= ~ButtonStates.Mousedown;
        Image = ((ButtonState & ButtonStates.Mouseover) != 0) ? Mouseover : idle;
    }

    #endregion
}

[Serializable]
internal class ImageButtonToolboxItem : ToolboxItem
{
    public ImageButtonToolboxItem() : base(typeof(ImageButton)) { }

    protected ImageButtonToolboxItem(SerializationInfo info, StreamingContext context)
    {
        Deserialize(info, context);
    }

    protected override IComponent[] CreateComponentsCore(IDesignerHost host)
    {
        ImageButton imageButton = (ImageButton)host.CreateComponent(typeof(ImageButton));

        Assembly assembly = Assembly.GetAssembly(typeof(ImageButton));

        using (Stream streamMouseover = assembly.GetManifestResourceStream("Mvc.Mouseover.png"))
        using (Stream streamMousedown = assembly.GetManifestResourceStream("Mvc.Mousedown.png"))
        using (Stream streamIdle = assembly.GetManifestResourceStream("Mvc.Idle.png"))
        {
            imageButton.Idle = Image.FromStream(streamIdle);
            imageButton.Mouseover = Image.FromStream(streamMouseover);
            imageButton.Mousedown = Image.FromStream(streamMousedown);
        }

        return new IComponent[] { imageButton };
    }
}

internal class ImageButtonDesigner : ControlDesigner
{
    protected override void PostFilterAttributes(System.Collections.IDictionary attributes)
    {
        base.PostFilterAttributes(attributes);

        Attribute dockingBehaviour = new DockingAttribute(DockingBehavior.Never);

        attributes[typeof(DockingAttribute)] = dockingBehaviour;
    }

    public override SelectionRules SelectionRules
    {
        get
        {
            return SelectionRules.Moveable;
        }
    }
}

抱歉工具箱项目和设计器代码凌乱..

我的问题是，是否需要任何特殊的实现方式才能使按钮控件在模态表单上工作（与普通按钮一样） （注意，Form 的 BorderStyle 属性设置为 None，不知道是否重要）

谢谢，提前！

Answer 1

您需要实际应用分配的 DialogResult 属性，它不是自动的。通过覆盖 OnClick() 方法来做到这一点：

protected override void OnClick(EventArgs e) {
    var form = this.FindForm();
    if (form != null) form.DialogResult = dialogResult;
    base.OnClick(e);
}

从技术上讲，您还应该将状态更改通知可访问性客户端，完全不清楚您是否关心这一点。对于自定义控件，它往往会被跳过，但您通常应该这样做。在 base.OnClick() 调用之前插入这些语句：

    base.AccessibilityNotifyClients(AccessibleEvents.StateChange, -1);
    base.AccessibilityNotifyClients(AccessibleEvents.NameChange, -1);