何かをするまで待つ処理をしたい

'めんどくさかったのでTextBoxを1個はっつけたユーザーコントロールを使用
Public Class UserControl1

    Private EnabledProperties As New ArrayList()
    Public Event 入力完了()

    Private Sub UserControl1_Load( _
    ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        TextBox1.Visible = False
    End Sub

    Public Sub 入力待ち()
        TextBox1.Text = ""
        TextBox1.Visible = True
        EnabledProperties.Clear()
        For i As Integer = 0 To ParentForm.Controls.Count - 1
            If Not ParentForm.Controls(i).Equals(Me) Then
                EnabledProperties.Add(ParentForm.Controls(i).Enabled)
                ParentForm.Controls(i).Enabled = False
            Else
                EnabledProperties.Add(True)
            End If
        Next
    End Sub

    Private Sub TextBox1_KeyDown( _
    ByVal sender As Object, _
    ByVal e As System.Windows.Forms.KeyEventArgs) Handles TextBox1.KeyDown
        If e.KeyCode = Windows.Forms.Keys.Enter Then
            For i As Integer = 0 To ParentForm.Controls.Count - 1
                If Not ParentForm.Controls(i).Equals(Me) Then
                    ParentForm.Controls(i).Enabled = CBool(EnabledProperties(i))
                End If
            Next
            TextBox1.Visible = False
            RaiseEvent 入力完了()
        End If
    End Sub

    Public ReadOnly Property 入力データ() As String
        Get
            Return Me.TextBox1.Text
        End Get
    End Property

End Class

'そのユーザーコントロールをはっつけたForm
Public Class Form1

    Private Sub Button1_Click( _
    ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        AddHandler UserControl11.入力完了, AddressOf Button1_Click_つづき
        UserControl11.入力待ち()
    End Sub

    Private Sub Button1_Click_つづき()
        RemoveHandler UserControl11.入力完了, AddressOf Button1_Click_つづき
        MsgBox("Button1:" & UserControl11.入力データ)
    End Sub

    Private Sub Button2_Click( _
    ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        AddHandler UserControl11.入力完了, AddressOf Button2_Click_つづき
        UserControl11.入力待ち()
    End Sub

    Private Sub Button2_Click_つづき()
        RemoveHandler UserControl11.入力完了, AddressOf Button2_Click_つづき
        MsgBox("Button2:" & UserControl11.入力データ)
    End Sub

End Class

for (;;)
{
	MSG msg;
	GetMessage(&msg, NULL, 0, 0);

	switch (msg.message) {
	case WM_AAAA:
		if (モーダルループを抜ける条件)
		goto ExitLoop;

	case WM_BBBB:
		// モーダルなメッセージ処理１
		break;

	case WM_CCCC:
		// モーダルなメッセージ処理２
		break;

	case WM_DDDD:
	case WM_EEEE:
		// これらのメッセージはディスパッチする
		DispatchMessage(&msg);
		break;

	・・・

	}
}

Public Class CustomTextBox
    Inherits System.Windows.Forms.TextBox

    Public Function 入力() As String

        Me.Text = String.Empty

        Do Until Me.Text.Length >= 5
            WaitMessage()
            Application.DoEvents()
        Loop

        Return Me.Text

    End Function

    Declare Function WaitMessage Lib "user32.dll" () As Boolean
End Class