我有一个在WinForms中运行良好的搜索框，但在WPF中给我带来了麻烦。
每次推送信件时都会启动搜索，类似于Google。
If (txtQuickSearch.Text.Length >= 3) Or (e.Key = Key.Enter) Then
If SearchWorker.IsBusy Then
SearchWorker.CancelAsync()
Do While SearchWorker.IsBusy
'Application.DoEvents()
'System.Threading.Thread.Sleep(500)
Loop
End If
doSearchText = txtQuickSearch.Text
SearchWorker.RunWorkerAsync()
End If
每次按下某个键，它都会取消当前的searchWorker，然后重新启动它。在WinForms中Do while searchworker.isbusy doevents loop工作得很好，但由于我无法访问它，我需要找到一个更好的方法来实现它。 Sleep（）死了，我试过把i + = 1作为一种通过时间直到它不忙的方式，但这也不起作用...
我该怎么办？
更新：这是我改变它的内容。它工作，但取消部分似乎没有触发，这似乎没有运行异步...
Imports System.ComponentModel
Imports System.Collections.ObjectModel
Imports System.Threading
Imports System.Threading.Tasks
Public Class QuickSearch
Private doSearchText As String
Private canceled As Boolean
Private curSearch As String
Dim searchResults As New ObservableCollection(Of ocSearchResults)
'Task Factory
Private cts As CancellationTokenSource
Private searchtask As Task(Of ObservableCollection(Of ocSearchResults))
Private Sub txtQuickSearch_KeyDown(ByVal sender As System.Object, ByVal e As System.Windows.Input.KeyEventArgs) Handles txtQuickSearch.KeyDown
If e.Key = Key.Enter Then
curSearch = ""
End If
If ((txtQuickSearch.Text.Length >= 3) Or (e.Key = Key.Enter)) And Not txtQuickSearch.Text = curSearch Then
If Not cts Is Nothing Then
cts.Cancel()
ColorChecker.CancelAsync()
Try
' searchtask.Wait()
Catch ex As AggregateException
MsgBox(ex.InnerException.Message)
End Try
cts = New CancellationTokenSource
Else
cts = New CancellationTokenSource
End If
Dim cToken = cts.Token
Me.Height = 400
doSearchText = txtQuickSearch.Text
'This always completes fully before continuing on to tRunWorkerComplete(searchtask.Result) '
searchtask = Task(Of ObservableCollection(Of ocSearchResults)).Factory.StartNew(Function() tPerformSearch(cToken), cToken)
Try
tRunWorkerCompleted(searchtask.Result)
Catch ex As AggregateException
' MsgBox(ex.InnerException.Message)
End Try
Else
If Not cts Is Nothing Then
cts.Cancel()
End If
searchResults.Clear()
End If
End Sub
Function tPerformSearch(ByVal ct As CancellationToken) As ObservableCollection(Of ocSearchResults)
On Error GoTo sError
canceled = False
If curSearch = doSearchText Then
canceled = True
Return Nothing
End If
curSearch = doSearchText
Dim SR As New ObservableCollection(Of ocSearchResults)
Dim t As ocSearchResults
Dim rSelect As New ADODB.Recordset
Dim sSql As String = "SELECT DISTINCT CustomerID, CustomerName, City, State, Zip FROM qrySearchFieldsQuick WHERE "
Dim sWhere As String = "CustomerName Like '" & doSearchText & "%'"
SR.Clear()
With rSelect
.Open(sSql & sWhere & " ORDER BY CustomerName", MyCn, ADODB.CursorTypeEnum.adOpenStatic, ADODB.LockTypeEnum.adLockReadOnly)
Do While Not .EOF
If ct.IsCancellationRequested Then ' This never shows true, the process always returns a value, as if it wasn't async'
canceled = True
Return Nothing
End If
Do While IsDBNull(.Fields("CustomerID").Value)
.MoveNext()
Loop
t = New ocSearchResults(.Fields!CustomerID.Value, .Fields!CustomerName.Value.ToString.Trim, .Fields!City.Value.ToString.Trim, .Fields!State.Value.ToString.Trim, .Fields!Zip.Value.ToString.Trim)
If Not SR.Contains(t) Then
SR.Add(t)
End If
aMoveNext:
.MoveNext()
Loop
.Close()
End With
Return SR
Exit Function
sError:
MsgBox(ErrorToString, MsgBoxStyle.Exclamation)
End Function
Sub tRunWorkerCompleted(ByVal SR As ObservableCollection(Of ocSearchResults))
If canceled Then
Exit Sub
End If
If cts.IsCancellationRequested Then
Exit Sub
End If
searchResults.Clear()
For Each t As ocSearchResults In SR
searchResults.Add(t)
Next
ColorChecker = New BackgroundWorker
ColorChecker.WorkerReportsProgress = True
ColorChecker.WorkerSupportsCancellation = True
ColorChecker.RunWorkerAsync(searchResults)
lblRecordCount.Text = "(" & searchResults.Count & ") Records"
progBar.Value = 100
Exit Sub
sError:
MsgBox(ErrorToString)
End Sub
答案 0 :(得分：2)
我不太了解VB给你任何写得很好的示例代码，但如果你使用的是.Net 4.0，我建议切换到System.Threading.Tasks命名空间，该命名空间有cancellation abilities。
If (txtQuickSearch.Text.Length >= 3) Or (e.Key = Key.Enter) Then
If TokenSource Is Not Nothing Then
TokenSource.Cancel()
TokenSource = New CancellationTokenSource()
End If
Task.Factory.StartNew(SomeSearchMethod, txtQuickSearch.Text, TokenSource.Token)
End If
答案 1 :(得分：2)
我不确定BackgroundWorker是否足够灵活，无论如何都能为这种类型的后台处理提供优雅的解决方案。我想我要做的是创建一个专门的线程来进行搜索。该线程将使用生产者 - 消费者模式来接受工作项并对其进行处理。
以下代码是我如何看待此策略工作的草图。您可以调用SearchAsync方法来请求新搜索。该方法接受在搜索操作找到某些内容时调用的回调。请注意，如果另一个搜索请求排队，则使用者代码（在Run方法中）会取消其当前的搜索操作。结果是消费者只处理最新的请求。
Public Class Searcher
Private m_Queue As BlockingCollection(Of WorkItem) = New BlockingCollection(Of WorkItem)()
Public Sub New()
Dim t = New Thread(AddressOf Run)
t.IsBackground = True
t.Start()
End Sub
Public Sub SearchAsync(ByVal text As String, ByVal callback As Action)
Dim wi = New WorkItem()
wi.Text = text
wi.Callback = callback
m_Queue.Add(wi)
End Sub
Private Sub Run()
Do While True
Dim wi As WorkItem = m_Queue.Take()
Dim found As Boolean = False
Do While Not found AndAlso m_Queue.Count = 0
' Continue searching using your custom algorithm here.
Loop
If found Then
wi.Callback()
End If
Loop
End Sub
Private Class WorkItem
Public Text As String
Public Callback As Action
End Class
End Class
这是优雅发生的地方。看看如何从UI线程实现逻辑。
If (txtQuickSearch.Text.Length >= 3) Or (e.Key = Key.Enter) Then
searcher.SearchAsync(txtQuickSearch.Text, AddressOf OnSearchComplete)
End If
请注意，OnSearchComplete将在工作线程上执行，因此如果要将结果发布到UI控件，则需要从回调中调用Dispatcher.Invoke。
答案 2 :(得分：0)
您可以通过执行（在C＃中）来模拟WPF中的DoEvents：
Dispatcher.Invoke（DispatcherPriority.Background，new Action（（）=＆gt; {}））;