原文： http://zetcode.com/gui/vbwinforms/dialogs/

在 Visual Basic Winforms 教程的这一部分中，我们将讨论对话框。

对话框窗口或对话框是大多数现代 GUI 应用必不可少的部分。 对话被定义为两个或更多人之间的对话。 在计算机应用中，对话框是一个窗口，用于与应用“对话”。 对话框用于输入数据，修改数据，更改应用设置等。对话框是用户与计算机程序之间进行通信的重要手段。

基本上有两种类型的对话框。 预定义对话框和自定义对话框。

FolderBrowserDialog

此对话框提示用户选择一个文件夹。

  1. ' ZetCode Mono Visual Basic Winforms tutorial
  2. '
  3. ' In this program we select a directory with a
  4. ' FolderBrowser dialog. The selected directory's
  5. ' name is shown in the statusbar. 
  6. '
  7. ' author jan bodnar
  8. ' last modified May 2009
  9. ' website www.zetcode.com
  11. Imports System.Windows.Forms
  12. Imports System.Drawing
  14. Public Class WinVBApp
  15.     Inherits Form
  17.     Dim statusbar As StatusBar
  19.     Public Sub New
  21.        Me.Text = "FolderBrowserDialog"
  22.        Me.Size = New Size(300, 250)
  24.        Me.InitUI
  26.        Me.CenterToScreen
  28.     End Sub
  30.     Private Sub InitUI
  32.         Dim toolbar As New ToolBar
  33.         Dim open As New ToolBarButton
  35.         statusbar = New StatusBar
  36.         statusbar.Parent = Me
  38.         toolbar.Buttons.Add(open)
  40.         Me.Controls.Add(toolbar)
  42.         AddHandler toolbar.ButtonClick, AddressOf Me.OnClicked
  44.     End Sub
  46.     Private Sub OnClicked(ByVal sender As Object, _
  47.                     ByVal e As ToolBarButtonClickEventArgs)
  49.         Dim dialog As New FolderBrowserDialog
  51.         If dialog.ShowDialog(Me) = DialogResult.OK
  52.            statusbar.Text = dialog.SelectedPath
  53.         End If
  55.     End Sub
  57.     Public Shared Sub Main
  58.         Application.Run(New WinVBApp)
  59.     End Sub
  61. End Class

我们有一个工具栏和一个工具栏按钮。 点击按钮，FolderBrowserDialog出现在屏幕上。 所选文件夹的名称显示在状态栏中。

  1. Dim dialog As New FolderBrowserDialog

FolderBrowserDialog已创建。

  1. If dialog.ShowDialog(Me) = DialogResult.OK
  2.     statusbar.Text = dialog.SelectedPath
  3. End If

ShowDialog方法在屏幕上显示对话框。 如果单击对话框的“确定”按钮，则所选的目录路径将显示在状态栏上。

对话框 - 图1

图：FolderBrowserDialog

ColorDialog

此对话框显示可用的颜色以及使用户能够定义自定义颜色的控件。

  1. ' ZetCode Mono Visual Basic Winforms tutorial
  2. '
  3. ' In this program we use the ColorDialog
  4. ' to change a color of a rectangle
  5. '
  6. ' author jan bodnar
  7. ' last modified May 2009
  8. ' website www.zetcode.com
  10. Imports System.Windows.Forms
  11. Imports System.Drawing
  13. Public Class WinVBApp
  14.     Inherits Form
  16.     Private col As Color
  18.     Private Const rectWidth As Integer = 100
  19.     Private Const rectHeight As Integer = 100
  20.     Private Dim r As Rectangle
  22.     Public Sub New
  24.        Me.Text = "ColorDialog"
  25.        Me.Size = New Size(300, 250)
  27.        Me.InitUI
  29.        Me.CenterToScreen
  31.     End Sub
  33.     Private Sub InitUI
  35.         Dim tbar As New ToolBar
  36.         Dim open As New ToolBarButton
  38.         col = Color.Blue
  40.         tbar.Buttons.Add(open)
  42.         Me.LocateRect
  44.         Me.SetStyle(ControlStyles.ResizeRedraw, True)
  45.         Controls.Add(tbar)
  47.         AddHandler Me.Paint, AddressOf Me.OnPaint
  48.         AddHandler tbar.ButtonClick, AddressOf Me.OnClicked
  50.     End Sub
  52.     Private Sub OnPaint(ByVal sender As Object, ByVal e As PaintEventArgs)
  54.       Dim g As Graphics = e.Graphics
  55.       Me.LocateRect
  57.       Dim brsh As New SolidBrush(col)
  59.       g.FillRectangle(brsh, r)    
  61.     End Sub
  63.     Private Sub OnClicked(ByVal sender As Object, _ 
  64.                     ByVal e As ToolBarButtonClickEventArgs)
  66.        Dim dialog As New ColorDialog
  68.        If dialog.ShowDialog(Me) = DialogResult.OK
  69.           col = dialog.Color
  70.           Me.Invalidate
  71.        End If
  73.     End Sub
  75.     Private Sub LocateRect
  76.         Dim x As Integer = (Me.ClientSize.Width - rectWidth) / 2
  77.         Dim y As Integer = (Me.ClientSize.Height - rectHeight) / 2
  78.         r = New Rectangle(x, y, rectWidth, rectHeight)
  79.     End Sub
  81.     Public Shared Sub Main
  82.         Application.Run(New WinVBApp)
  83.     End Sub
  85. End Class

在此代码示例中，我们使用ColorDialog为位于窗体控件中间的矩形选择颜色。

  1. col = Color.Blue

开始时，矩形的颜色是蓝色。 我们使用col变量来确定矩形的颜色。

  1. Dim dialog As New ColorDialog

ColorDialog已创建。

  1. If dialog.ShowDialog(Me) = DialogResult.OK
  2.   col = dialog.Color
  3.   Me.Invalidate
  4. End If

该代码显示颜色对话框。 如果单击“确定”按钮，则将获得选定的颜色并调用Invalidate方法。 该方法会使控件的整个表面无效，并使控件重画。 结果是用新的颜色值绘制了矩形。

对话框 - 图2

图：ColorDialog

FontDialog

FontDialog用于选择字体。

  1. ' ZetCode Mono Visual Basic Winforms tutorial
  2. '
  3. ' In this program we use the FontDialog
  4. ' to change a font of a label
  5. '
  6. ' author jan bodnar
  7. ' last modified May 2009
  8. ' website www.zetcode.com
  10. Imports System.Windows.Forms
  11. Imports System.Drawing
  13. Public Class WinVBApp
  14.     Inherits Form
  16.     Private Dim txt As Label
  18.     Public Sub New
  20.        Me.Text = "FontDialog"
  21.        Me.Size = New Size(300, 250)
  23.        Me.InitUI
  25.        Me.CenterToScreen
  27.     End Sub
  29.     Private Sub InitUI
  31.         Dim tbar As New ToolBar
  32.         tbar.Parent = Me
  34.         Dim open As New ToolBarButton
  35.         tbar.Buttons.Add(open)
  37.         txt = New Label
  38.         txt.Parent = Me
  39.         txt.Text = "Winforms tutorial"
  41.         Me.LocateText
  43.         txt.AutoSize = True
  45.         AddHandler Me.Resize, AddressOf Me.OnResize
  46.         AddHandler tbar.ButtonClick, AddressOf Me.OnClicked
  48.     End Sub
  50.     Private Sub OnClicked(ByVal sender As Object, _ 
  51.                     ByVal e As ToolBarButtonClickEventArgs)
  53.        Dim dialog As New FontDialog
  55.        If dialog.ShowDialog(Me) = DialogResult.OK
  56.           txt.Font = dialog.Font
  57.           Me.LocateText
  58.        End If
  60.     End Sub
  62.     Private Sub LocateText
  63.         txt.Top = (Me.ClientSize.Height - txt.Height) / 2
  64.         txt.Left = (Me.ClientSize.Width - txt.Width) / 2
  65.     End Sub
  67.     Private Sub OnResize(ByVal sender As Object, ByVal e As EventArgs)
  68.          Me.LocateText
  69.     End Sub
  71.     Public Shared Sub Main
  72.         Application.Run(New WinVBApp)
  73.     End Sub
  75. End Class

我们在表单控件的中间绘制一些文本。 我们使用字体对话框更改此文本的字体。

  1. Dim dialog As New FontDialog

FontDialog已创建。

  1. If dialog.ShowDialog(Me) = DialogResult.OK
  2.   txt.Font = dialog.Font
  3.   Me.LocateText
  4. End If

单击“确定”按钮时，将为Label控件设置新选择的字体。 由于文本的大小会随着字体的变化而变化，因此我们必须调用LocateText方法，该方法将文本定位在表单控件的中间。

对话框 - 图3

图：FontDialog

OpenDialog

此对话框用于打开文件。

  1. ' ZetCode Mono Visual Basic Winforms tutorial
  2. '
  3. ' In this program we use the OpenDialog to
  4. ' open a file and show its contents in 
  5. ' a TextBox control
  6. '
  7. ' author jan bodnar
  8. ' last modified May 2009
  9. ' website www.zetcode.com
  11. Imports System.Windows.Forms
  12. Imports System.Drawing
  13. Imports System.IO
  15. Public Class WinVBApp
  16.     Inherits Form
  18.     Private txtBox As TextBox
  20.     Public Sub New
  22.        Me.Text = "OpenDialog"
  23.        Me.Size = New Size(300, 250)
  25.        Me.InitUI
  27.        Me.CenterToScreen
  29.     End Sub
  31.     Private Sub InitUI
  33.         Dim tbar As New ToolBar
  34.         tbar.Parent = Me
  36.         Dim open As New ToolBarButton
  37.         tbar.Buttons.Add(open)
  39.         txtBox = New TextBox
  40.         txtBox.Parent = Me
  41.         txtBox.Multiline = True
  42.         txtBox.ScrollBars = ScrollBars.Both
  43.         txtBox.WordWrap = False
  44.         txtBox.Parent = Me
  45.         txtBox.Dock = DockStyle.Fill
  47.         AddHandler tbar.ButtonClick, AddressOf Me.OnClicked
  49.     End Sub
  51.     Private Sub OnClicked(ByVal sender As Object, _ 
  52.                     ByVal e As ToolBarButtonClickEventArgs)
  54.        Dim dia As New OpenFileDialog
  55.        dia.Filter = "VB files (*.vb)|*.vb"
  57.        If dia.ShowDialog(Me) = DialogResult.OK
  59.            Dim reader As New StreamReader(dia.FileName)
  60.            Dim data As String = reader.ReadToEnd
  62.            reader.Close
  63.            txtBox.Text = data
  65.        End If
  67.     End Sub
  69.     Public Shared Sub Main
  70.         Application.Run(New WinVBApp)
  71.     End Sub
  73. End Class

我们使用OpenDialog控件打开 VB 源文件。 我们有一个TextBox控件，用于显示文件。

  1. Dim dia As New OpenFileDialog

OpenDialog已创建。

  1. dia.Filter = "VB files (*.vb)|*.vb"

我们将Filter属性设置为 VB 源文件。 此对话框实例只能选择 VB 文件。

  1. If dia.ShowDialog(Me) = DialogResult.OK
  3.     Dim reader As New StreamReader(dia.FileName)
  4.     Dim data As String = reader.ReadToEnd
  6.     reader.Close
  7.     txtBox.Text = data
  9. End If

单击确定后，我们读取所选文件的内容并将其放入TextBox控件。

对话框 - 图4

图：OpenDialog

在 Visual Basic Winforms 教程的这一部分中，我们显示了各种对话框。