我有一个带有文本框的自定义用户控件，我想在自定义控件之外显示基线(文本框中的文本)对齐线。我知道我们创建了一个设计器(从ControlDesigner继承)，并且重写了SnapLines以访问细线，但是我想知道如何获取自定义用户控件公开的控件的文本基线。

解决方案

我们走在正确的轨道上。我们将需要在设计器中覆盖SnapLines属性，并执行以下操作：

Public Overrides ReadOnly Property SnapLines() As System.Collections.IList
    Get
        Dim snapLinesList As ArrayList = TryCast(MyBase.SnapLines, ArrayList)

        Dim offset As Integer
        Dim ctrl As MyControl = TryCast(Me.Control, MyControl)
        If ctrl IsNot Nothing AndAlso ctrl.TextBox1 IsNot Nothing Then
            offset = ctrl.TextBox1.Bottom - 5
        End If

        snapLinesList.Add(New SnapLine(SnapLineType.Baseline, offset, SnapLinePriority.Medium))

        Return snapLinesList

    End Get
End Property

在此示例中，用户控件包含一个文本框。该代码添加了一个新的捕捉线，该捕捉线表示文本框的基线。重要的是要正确计算偏移量。

我只是有一个类似的需求，我这样解决了它：

public override IList SnapLines
{
    get
    {
        IList snapLines = base.SnapLines;

        MyControl control = Control as MyControl;
        if (control == null) { return snapLines; }

        IDesigner designer = TypeDescriptor.CreateDesigner(
            control.textBoxValue, typeof(IDesigner));
        if (designer == null) { return snapLines; }
        designer.Initialize(control.textBoxValue);

        using (designer)
        {
            ControlDesigner boxDesigner = designer as ControlDesigner;
            if (boxDesigner == null) { return snapLines; }

            foreach (SnapLine line in boxDesigner.SnapLines)
            {
                if (line.SnapLineType == SnapLineType.Baseline)
                {
                    snapLines.Add(new SnapLine(SnapLineType.Baseline,
                        line.Offset + control.textBoxValue.Top,
                        line.Filter, line.Priority));
                    break;
                }
            }
        }

        return snapLines;
    }
}

这样，它实际上为子控件创建了一个临时子设计器，以找出"实际"基线对齐线在哪里。

这似乎在测试中表现合理，但是如果担心性能问题(并且内部文本框不移动)，则可以将大部分代码提取到Initialize方法中。

这也假定文本框是UserControl的直接子级。如果还有其他影响布局的控件，则偏移量计算将变得更加复杂。

作为Miral答案的更新..这里是一些"缺失的步骤"，对于正在寻找如何做到这一点的新手。 :)上面的Ccode几乎可以"直接插入"，除了更改一些值以引用将要修改的UserControl之外。

可能需要的参考：
System.Design(@robyaw)

需要的用途：

using System.Windows.Forms.Design;
using System.Windows.Forms.Design.Behavior;
using System.ComponentModel;
using System.ComponentModel.Design;
using System.Collections;

在UserControl上，我们需要以下属性：

[Designer(typeof(MyCustomDesigner))]

然后，我们需要一个"设计器"类，该类将具有SnapLines覆盖：

private class MyCustomerDesigner : ControlDesigner {
  public override IList SnapLines {
    get {
     /* Code from above */
    IList snapLines = base.SnapLines;

    // *** This will need to be modified to match your user control
    MyControl control = Control as MyControl;
    if (control == null) { return snapLines; }

    // *** This will need to be modified to match the item in your user control
    // This is the control in your UC that you want SnapLines for the entire UC
    IDesigner designer = TypeDescriptor.CreateDesigner(
        control.textBoxValue, typeof(IDesigner));
    if (designer == null) { return snapLines; }

    // *** This will need to be modified to match the item in your user control
    designer.Initialize(control.textBoxValue);

    using (designer)
    {
        ControlDesigner boxDesigner = designer as ControlDesigner;
        if (boxDesigner == null) { return snapLines; }

        foreach (SnapLine line in boxDesigner.SnapLines)
        {
            if (line.SnapLineType == SnapLineType.Baseline)
            {
                // *** This will need to be modified to match the item in your user control
                snapLines.Add(new SnapLine(SnapLineType.Baseline,
                    line.Offset + control.textBoxValue.Top,
                    line.Filter, line.Priority));
                break;
            }
        }
    }

    return snapLines;
}

    }
  }
}

VB.Net版本：
注意：我们必须将txtDescription更改为文本框或者使用的其他内部控件名称。和ctlUserControl到usercontrol名称

<Designer(GetType(ctlUserControl.MyCustomDesigner))> _
Partial Public Class ctlUserControl
   '... 
   'Your Usercontrol class specific code
   '... 
    Class MyCustomDesigner
        Inherits ControlDesigner
        Public Overloads Overrides ReadOnly Property SnapLines() As IList
            Get
                ' Code from above 

                Dim lines As IList = MyBase.SnapLines

                ' *** This will need to be modified to match your user control
                Dim control__1 As ctlUserControl = TryCast(Me.Control, ctlUserControl)
                If control__1 Is Nothing Then Return lines

                ' *** This will need to be modified to match the item in your user control
                ' This is the control in your UC that you want SnapLines for the entire UC
                Dim designer As IDesigner = TypeDescriptor.CreateDesigner(control__1.txtDescription, GetType(IDesigner))
                If designer Is Nothing Then
                    Return lines
                End If

                ' *** This will need to be modified to match the item in your user control
                designer.Initialize(control__1.txtDescription)

                Using designer
                    Dim boxDesigner As ControlDesigner = TryCast(designer, ControlDesigner)
                    If boxDesigner Is Nothing Then
                        Return lines
                    End If

                    For Each line As SnapLine In boxDesigner.SnapLines
                        If line.SnapLineType = SnapLineType.Baseline Then
                            ' *** This will need to be modified to match the item in your user control
                            lines.Add(New SnapLine(SnapLineType.Baseline, line.Offset + control__1.txtDescription.Top, line.Filter, line.Priority))
                            Exit For
                        End If
                    Next
                End Using

                Return lines
            End Get
        End Property
    End Class

End Class

感谢所有这些人的帮助。这是一项艰巨的任务。在每个UserControl中都有一个私有子类的想法不是很可口。

我想出了这个基础课程来提供帮助。

[Designer(typeof(UserControlSnapLineDesigner))]
public class UserControlBase : UserControl
{
    protected virtual Control SnapLineControl { get { return null; } }

    private class UserControlSnapLineDesigner : ControlDesigner
    {
        public override IList SnapLines
        {
            get
            {
                IList snapLines = base.SnapLines;

                Control targetControl = (this.Control as UserControlBase).SnapLineControl;

                if (targetControl == null)
                    return snapLines;

                using (ControlDesigner controlDesigner = TypeDescriptor.CreateDesigner(targetControl,
                    typeof(IDesigner)) as ControlDesigner)
                {
                    if (controlDesigner == null)
                        return snapLines;

                    controlDesigner.Initialize(targetControl);

                    foreach (SnapLine line in controlDesigner.SnapLines)
                    {
                        if (line.SnapLineType == SnapLineType.Baseline)
                        {
                            snapLines.Add(new SnapLine(SnapLineType.Baseline, line.Offset + targetControl.Top,
                                line.Filter, line.Priority));
                            break;
                        }
                    }
                }
                return snapLines;
            }
        }
    }
}

接下来，从此基础派生UserControl：

public partial class MyControl : UserControlBase
{
    protected override Control SnapLineControl
    {
        get
        {
            return txtTextBox;
        }
    }

    ...

}

再次感谢我们发布此信息。