多執行緒 Windows Form 控制項範例
Windows Form 使用單一執行緒 Apartment Model (STA)，因為 Windows Form 的架構是以本質上即是 Apartment 執行緒的原生 Win32 Windows 為基礎。STA 模型表示可以在任何執行緒上建立視窗，但建立後則不可以在執行緒間切換，且所有呼叫它的函式必須存在於它的建立執行緒上。除了 Windows Form 以外，.NET Framework 中的類別是使用無限制執行緒模型 (Free Threading Model)。如需 .NET Framework 中的執行緒詳細資訊，請參閱執行緒處理。
STA 模型對需在控制項的建立執行緒之外呼叫的控制項，會要求該控制項的任何方法必須封送 (Marshal) 給 (執行於) 控制項的建立執行緒處理。Control 基底類別 (Base Class) 為此提供了數個方法 (Invoke、BeginInvoke 和 EndInvoke)。Invoke 執行同步方法呼叫；BeginInvoke 則執行非同步方法呼叫。
當您在控制項中使用多執行緒來處理耗用資源的工作時，因為耗用資源的作業是在背景 (Background) 執行緒上執行，所以使用者介面仍然可以正常回應。
下列範例 (DirectorySearcher) 將說明一個使用背景執行緒的多執行緒 Windows Form 控制項，它將以指定的搜尋字串遞迴搜尋目錄中相符的檔案，然後將搜尋結果填入 (Populate) 清單方塊。以下為範例中所描述的重要概念。
DirectorySearcher將啟動一個新執行緒以執行搜尋作業。之後執行ThreadProcedure方法的執行緒會呼叫 HelperRecurseDirectory方法以執行實際的搜尋和填入清單方塊作業。但是，填入清單方塊作業需要執行的跨執行緒 (Cross-Thread) 呼叫將在稍後的項目符號中說明。DirectorySearcher會定義將檔案加入至清單方塊的AddFiles方法；而RecurseDirectory則不可以直接叫用AddFiles，因為AddFiles只可在建立DirectorySearcher的 STA 執行緒中執行。RecurseDirectory可以呼叫AddFiles的唯一方法是透過跨執行緒呼叫 - 即呼叫 Invoke 或 BeginInvoke 而將AddFiles封送給DirectorySearcher的建立執行緒處理。RecurseDirectory使用 BeginInvoke 以執行非同步呼叫。- 將方法封送處理需要使用函式指標或回呼 (Callback)。.NET Framework 中的委派 (Delegate) 可以完成這項工作。BeginInvoke 會取得一個委派作為引數。
DirectorySearcher即可定義一個委派 (FileListDelegate)、在它的建構函式 (Constructor) 中將AddFiles繫結於FileListDelegate的執行個體 (Instance) 然後將這個委派執行個體傳遞給 BeginInvoke。DirectorySearcher同時也會定義在完成搜尋後要封送處理的委派事件。
Option Strict
Option Explicit
Imports System
Imports System.IO
Imports System.Threading
Imports System.Windows.Forms
Namespace Microsoft.Samples.DirectorySearcher
' <summary>
' This class is a Windows Forms control that implements a simple directory searcher.
' You provide, through code, a search string and it will search directories on
' a background thread, populating its list box with matches.
' </summary>
Public Class DirectorySearcher
Inherits Control
' Define a special delegate that handles marshaling
' lists of file names from the background directory search
' thread to the thread that contains the list box.
Delegate Sub FileListDelegate(files() As String, startIndex As Integer, count As Integer)
Private _listBox As ListBox
Private _searchCriteria As String
Private _searching As Boolean
Private _deferSearch As Boolean
Private _searchThread As Thread
Private _fileListDelegate As FileListDelegate
Private _onSearchComplete As EventHandler
Public Sub New()
_listBox = New ListBox()
_listBox.Dock = DockStyle.Fill
Controls.Add(_listBox)
_fileListDelegate = New FileListDelegate(AddressOf AddFiles)
_onSearchComplete = New EventHandler(AddressOf OnSearchComplete)
End Sub
Public Property SearchCriteria() As String
Get
Return _searchCriteria
End Get
Set
' If currently searching, abort
' the search and restart it after
' setting the new criteria.
'
Dim wasSearching As Boolean = Searching
If wasSearching Then
StopSearch()
End If
_listBox.Items.Clear()
_searchCriteria = value
If wasSearching Then
BeginSearch()
End If
End Set
End Property
Public ReadOnly Property Searching() As Boolean
Get
Return _searching
End Get
End Property
Public Event SearchComplete As EventHandler
' <summary>
' This method is called from the background thread. It is called through
' a BeginInvoke call so that it is always marshaled to the thread that
' owns the list box control.
' </summary>
' <param name="files"></param>
' <param name="startIndex"></param>
' <param name="count"></param>
Private Sub AddFiles(files() As String, startIndex As Integer, count As Integer)
While count > 0
count -= 1
_listBox.Items.Add(files((startIndex + count)))
End While
End Sub
Public Sub BeginSearch()
' Create the search thread, which
' will begin the search.
' If already searching, do nothing.
'
If Searching Then
Return
End If
' Start the search if the handle has
' been created. Otherwise, defer it until the
' handle has been created.
If IsHandleCreated Then
_searchThread = New Thread(New ThreadStart(AddressOf ThreadProcedure))
_searching = True
_searchThread.Start()
Else
_deferSearch = True
End If
End Sub
Protected Overrides Sub OnHandleDestroyed(e As EventArgs)
' If the handle is being destroyed and you are not
' recreating it, then abort the search.
If Not RecreatingHandle Then
StopSearch()
End If
MyBase.OnHandleDestroyed(e)
End Sub
Protected Overrides Sub OnHandleCreated(e As EventArgs)
MyBase.OnHandleCreated(e)
If _deferSearch Then
_deferSearch = False
BeginSearch()
End If
End Sub
' <summary>
' This method is called by the background thread when it has
' finished the search.
' </summary>
' <param name="sender"></param>
' <param name="e"></param>
Private Sub OnSearchComplete(sender As Object, e As EventArgs)
RaiseEvent SearchComplete(sender, e)
End Sub
Public Sub StopSearch()
If Not _searching Then
Return
End If
If _searchThread.IsAlive Then
_searchThread.Abort()
_searchThread.Join()
End If
_searchThread = Nothing
_searching = False
End Sub
' <summary>
' Recurses the given path, adding all files on that path to
' the list box. After it finishes with the files, it
' calls itself once for each directory on the path.
' </summary>
' <param name="searchPath"></param>
Private Sub RecurseDirectory(searchPath As String)
' Split searchPath into a directory and a wildcard specification.
'
Dim directoryPath As String = Path.GetDirectoryName(searchPath)
Dim search As String = Path.GetFileName(searchPath)
' If a directory or search criteria are not specified, then return.
'
If directoryPath Is Nothing Or search Is Nothing Then
Return
End If
Dim files() As String
' File systems like NTFS that have
' access permissions might result in exceptions
' when looking into directories without permission.
' Catch those exceptions and return.
Try
files = Directory.GetFiles(directoryPath, search)
Catch e As UnauthorizedAccessException
Return
Catch e As DirectoryNotFoundException
Return
End Try
' Perform a BeginInvoke call to the list box
' in order to marshal to the correct thread. It is not
' very efficient to perform this marshal once for every
' file, so batch up multiple file calls into one
' marshal invocation.
Dim startingIndex As Integer = 0
While startingIndex < files.Length
' Batch up 20 files at once, unless at the
' end.
'
Dim count As Integer = 20
If count + startingIndex >= files.Length Then
count = files.Length - startingIndex
End If
' Begin the cross-thread call. Because you are passing
' immutable objects into this invoke method, you do not have to
' wait for it to finish. If these were complex objects, you would
' have to either create new instances of them or
' wait for the thread to process this invoke before modifying
' the objects.
Dim r As IAsyncResult = BeginInvoke(_fileListDelegate, New Object() {files, startingIndex, count})
startingIndex += count
End While
' Now that you have finished the files in this directory, recurse
' for each subdirectory.
Dim directories As String() = Directory.GetDirectories(directoryPath)
Dim d As String
For Each d In directories
RecurseDirectory(Path.Combine(d, search))
Next d
End Sub
'/ <summary>
'/ This is the actual thread procedure. This method runs in a background
'/ thread to scan directories. When finished, it simply exits.
'/ </summary>
Private Sub ThreadProcedure()
' Get the search string. Individual
' field assigns are atomic in .NET, so you do not
' need to use any thread synchronization to grab
' the string value here.
Try
Dim localSearch As String = SearchCriteria
' Now, search the file system.
'
RecurseDirectory(localSearch)
Finally
' You are done with the search, so update.
'
_searching = False
' Raise an event that notifies the user that
' the search has terminated.
' You do not have to do this through a marshaled call, but
' marshaling is recommended for the following reason:
' Users of this control do not know that it is
' multithreaded, so they expect its events to
' come back on the same thread as the control.
BeginInvoke(_onSearchComplete, New Object() {Me, EventArgs.Empty})
End Try
End Sub
End Class
End Namespace
[C#]
namespace Microsoft.Samples.DirectorySearcher
{
using System;
using System.IO;
using System.Threading;
using System.Windows.Forms;
/// <summary>
/// This class is a Windows Forms control that implements a simple directory searcher.
/// You provide, through code, a search string and it will search directories on
/// a background thread, populating its list box with matches.
/// </summary>
public class DirectorySearcher : Control
{
// Define a special delegate that handles marshaling
// lists of file names from the background directory search
// thread to the thread that contains the list box.
private delegate void FileListDelegate(string[] files, int startIndex, int count);
private ListBox listBox;
private string searchCriteria;
private bool searching;
private bool deferSearch;
private Thread searchThread;
private FileListDelegate fileListDelegate;
private EventHandler onSearchComplete;
public DirectorySearcher()
{
listBox = new ListBox();
listBox.Dock = DockStyle.Fill;
Controls.Add(listBox);
fileListDelegate = new FileListDelegate(AddFiles);
onSearchComplete = new EventHandler(OnSearchComplete);
}
public string SearchCriteria
{
get
{
return searchCriteria;
}
set
{
// If currently searching, abort
// the search and restart it after
// setting the new criteria.
//
bool wasSearching = Searching;
if (wasSearching)
{
StopSearch();
}
listBox.Items.Clear();
searchCriteria = value;
if (wasSearching)
{
BeginSearch();
}
}
}
public bool Searching
{
get
{
return searching;
}
}
public event EventHandler SearchComplete;
/// <summary>
/// This method is called from the background thread. It is called through
/// a BeginInvoke call so that it is always marshaled to the thread that
/// owns the list box control.
/// </summary>
/// <param name="files"></param>
/// <param name="startIndex"></param>
/// <param name="count"></param>
private void AddFiles(string[] files, int startIndex, int count)
{
while(count-- > 0)
{
listBox.Items.Add(files[startIndex + count]);
}
}
public void BeginSearch()
{
// Create the search thread, which
// will begin the search.
// If already searching, do nothing.
//
if (Searching)
{
return;
}
// Start the search if the handle has
// been created. Otherwise, defer it until the
// handle has been created.
if (IsHandleCreated)
{
searchThread = new Thread(new ThreadStart(ThreadProcedure));
searching = true;
searchThread.Start();
}
else
{
deferSearch = true;
}
}
protected override void OnHandleDestroyed(EventArgs e)
{
// If the handle is being destroyed and you are not
// recreating it, then abort the search.
if (!RecreatingHandle)
{
StopSearch();
}
base.OnHandleDestroyed(e);
}
protected override void OnHandleCreated(EventArgs e)
{
base.OnHandleCreated(e);
if (deferSearch)
{
deferSearch = false;
BeginSearch();
}
}
/// <summary>
/// This method is called by the background thread when it has finished
/// the search.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void OnSearchComplete(object sender, EventArgs e)
{
if (SearchComplete != null)
{
SearchComplete(sender, e);
}
}
public void StopSearch()
{
if (!searching)
{
return;
}
if (searchThread.IsAlive)
{
searchThread.Abort();
searchThread.Join();
}
searchThread = null;
searching = false;
}
/// <summary>
/// Recurses the given path, adding all files on that path to
/// the list box. After it finishes with the files, it
/// calls itself once for each directory on the path.
/// </summary>
/// <param name="searchPath"></param>
private void RecurseDirectory(string searchPath)
{
// Split searchPath into a directory and a wildcard specification.
//
string directory = Path.GetDirectoryName(searchPath);
string search = Path.GetFileName(searchPath);
// If a directory or search criteria are not specified, then return.
//
if (directory == null || search == null)
{
return;
}
string[] files;
// File systems like NTFS that have
// access permissions might result in exceptions
// when looking into directories without permission.
// Catch those exceptions and return.
try
{
files = Directory.GetFiles(directory, search);
}
catch(UnauthorizedAccessException)
{
return;
}
catch(DirectoryNotFoundException)
{
return;
}
// Perform a BeginInvoke call to the list box
// in order to marshal to the correct thread. It is not
// very efficient to perform this marshal once for every
// file, so batch up multiple file calls into one
// marshal invocation.
int startingIndex = 0;
while(startingIndex < files.Length)
{
// Batch up 20 files at once, unless at the
// end.
//
int count = 20;
if (count + startingIndex >= files.Length)
{
count = files.Length - startingIndex;
}
// Begin the cross-thread call. Because you are passing
// immutable objects into this invoke method, you do not have to
// wait for it to finish. If these were complex objects, you would
// have to either create new instances of them or
// wait for the thread to process this invoke before modifying
// the objects.
IAsyncResult r = BeginInvoke(fileListDelegate, new object[] {files, startingIndex, count});
startingIndex += count;
}
// Now that you have finished the files in this directory, recurse for
// each subdirectory.
string[] directories = Directory.GetDirectories(directory);
foreach(string d in directories)
{
RecurseDirectory(Path.Combine(d, search));
}
}
/// <summary>
/// This is the actual thread procedure. This method runs in a background
/// thread to scan directories. When finished, it simply exits.
/// </summary>
private void ThreadProcedure()
{
// Get the search string. Individual
// field assigns are atomic in .NET, so you do not
// need to use any thread synchronization to grab
// the string value here.
try
{
string localSearch = SearchCriteria;
// Now, search the file system.
//
RecurseDirectory(localSearch);
}
finally
{
// You are done with the search, so update.
//
searching = false;
// Raise an event that notifies the user that
// the search has terminated.
// You do not have to do this through a marshaled call, but
// marshaling is recommended for the following reason:
// Users of this control do not know that it is
// multithreaded, so they expect its events to
// come back on the same thread as the control.
BeginInvoke(onSearchComplete, new object[] {this, EventArgs.Empty});
}
}
}
}
在表單上使用多執行緒控制項
下列範例將說明如何在表單上使用多執行緒 DirectorySearcher 控制項。
Option Explicit
Option Strict
Imports Microsoft.Samples.DirectorySearcher
Imports System
Imports System.Drawing
Imports System.Collections
Imports System.ComponentModel
Imports System.Windows.Forms
Imports System.Data
Namespace SampleUsage
' <summary>
' Summary description for Form1.
' </summary>
Public Class Form1
Inherits System.Windows.Forms.Form
Private WithEvents directorySearcher As DirectorySearcher
Private searchText As System.Windows.Forms.TextBox
Private searchLabel As System.Windows.Forms.Label
Private WithEvents searchButton As System.Windows.Forms.Button
Public Sub New()
'
' Required for Windows Forms designer support.
'
InitializeComponent()
'
' Add any constructor code after InitializeComponent call here.
'
End Sub
#Region "Windows Form Designer generated code"
' <summary>
' Required method for designer support. Do not modify
' the contents of this method with the code editor.
' </summary>
Private Sub InitializeComponent()
Me.directorySearcher = New Microsoft.Samples.DirectorySearcher.DirectorySearcher()
Me.searchButton = New System.Windows.Forms.Button()
Me.searchText = New System.Windows.Forms.TextBox()
Me.searchLabel = New System.Windows.Forms.Label()
Me.directorySearcher.Anchor = System.Windows.Forms.AnchorStyles.Top Or System.Windows.Forms.AnchorStyles.Bottom Or System.Windows.Forms.AnchorStyles.Left Or System.Windows.Forms.AnchorStyles.Right
Me.directorySearcher.Location = New System.Drawing.Point(8, 72)
Me.directorySearcher.SearchCriteria = Nothing
Me.directorySearcher.Size = New System.Drawing.Size(271, 173)
Me.directorySearcher.TabIndex = 2
Me.searchButton.Location = New System.Drawing.Point(8, 16)
Me.searchButton.Size = New System.Drawing.Size(88, 40)
Me.searchButton.TabIndex = 0
Me.searchButton.Text = "&Search"
Me.searchText.Anchor = System.Windows.Forms.AnchorStyles.Top Or System.Windows.Forms.AnchorStyles.Left Or System.Windows.Forms.AnchorStyles.Right
Me.searchText.Location = New System.Drawing.Point(104, 24)
Me.searchText.Size = New System.Drawing.Size(175, 20)
Me.searchText.TabIndex = 1
Me.searchText.Text = "c:\*.cs"
Me.searchLabel.ForeColor = System.Drawing.Color.Red
Me.searchLabel.Location = New System.Drawing.Point(104, 48)
Me.searchLabel.Size = New System.Drawing.Size(176, 16)
Me.searchLabel.TabIndex = 3
Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
Me.ClientSize = New System.Drawing.Size(291, 264)
Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.searchLabel, Me.directorySearcher, Me.searchText, Me.searchButton})
Me.Text = "Search Directories"
End Sub
#End Region
' <summary>
' The main entry point for the application.
' </summary>
<STAThread()> _
Shared Sub Main()
Application.Run(New Form1())
End Sub
Private Sub searchButton_Click(sender As Object, e As System.EventArgs) Handles searchButton.Click
directorySearcher.SearchCriteria = searchText.Text
searchLabel.Text = "Searching..."
directorySearcher.BeginSearch()
End Sub
Private Sub directorySearcher_SearchComplete(sender As Object, e As System.EventArgs) Handles directorySearcher.SearchComplete
searchLabel.Text = String.Empty
End Sub
End Class
End Namespace
[C#]
namespace SampleUsage
{
using Microsoft.Samples.DirectorySearcher;
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
/// <summary>
/// Summary description for Form1.
/// </summary>
public class Form1 : System.Windows.Forms.Form
{
private DirectorySearcher directorySearcher;
private System.Windows.Forms.TextBox searchText;
private System.Windows.Forms.Label searchLabel;
private System.Windows.Forms.Button searchButton;
public Form1()
{
//
// Required for Windows Forms designer support.
//
InitializeComponent();
//
// Add any constructor code after InitializeComponent call here.
//
}
#region Windows Form Designer generated code
/// <summary>
/// Required method for designer support. Do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.directorySearcher = new Microsoft.Samples.DirectorySearcher.DirectorySearcher();
this.searchButton = new System.Windows.Forms.Button();
this.searchText = new System.Windows.Forms.TextBox();
this.searchLabel = new System.Windows.Forms.Label();
this.directorySearcher.Anchor = (((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom)
| System.Windows.Forms.AnchorStyles.Left)
| System.Windows.Forms.AnchorStyles.Right);
this.directorySearcher.Location = new System.Drawing.Point(8, 72);
this.directorySearcher.SearchCriteria = null;
this.directorySearcher.Size = new System.Drawing.Size(271, 173);
this.directorySearcher.TabIndex = 2;
this.directorySearcher.SearchComplete += new System.EventHandler(this.directorySearcher_SearchComplete);
this.searchButton.Location = new System.Drawing.Point(8, 16);
this.searchButton.Size = new System.Drawing.Size(88, 40);
this.searchButton.TabIndex = 0;
this.searchButton.Text = "&Search";
this.searchButton.Click += new System.EventHandler(this.searchButton_Click);
this.searchText.Anchor = ((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Left)
| System.Windows.Forms.AnchorStyles.Right);
this.searchText.Location = new System.Drawing.Point(104, 24);
this.searchText.Size = new System.Drawing.Size(175, 20);
this.searchText.TabIndex = 1;
this.searchText.Text = "c:\\*.cs";
this.searchLabel.ForeColor = System.Drawing.Color.Red;
this.searchLabel.Location = new System.Drawing.Point(104, 48);
this.searchLabel.Size = new System.Drawing.Size(176, 16);
this.searchLabel.TabIndex = 3;
this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
this.ClientSize = new System.Drawing.Size(291, 264);
this.Controls.AddRange(new System.Windows.Forms.Control[] {this.searchLabel,
this.directorySearcher,
this.searchText,
this.searchButton});
this.Text = "Search Directories";
}
#endregion
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
Application.Run(new Form1());
}
private void searchButton_Click(object sender, System.EventArgs e)
{
directorySearcher.SearchCriteria = searchText.Text;
searchLabel.Text = "Searching...";
directorySearcher.BeginSearch();
}
private void directorySearcher_SearchComplete(object sender, System.EventArgs e)
{
searchLabel.Text = string.Empty;
}
}
}