vb.net异步
一、无传入参数，无返回参数
- 写法1
Private Async Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim t1 As Task = Task.Run(Sub()
Dim RetS As String = ""
For i As Integer = 0 To 90000
RetS += "iiiiiiiiii"
Next
File.WriteAllText("2.txt", RetS)
End Sub)
Await t1
End Sub
- 写法2
Private Async Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim t2 As Task = Task.Run(New Action(AddressOf mWriteText))
Await t2
End Sub
Public Sub mWriteText()
Dim RetS As String = ""
For i As Integer = 0 To 90000
RetS += "iiiiiiiiii"
Next
File.WriteAllText("2.txt", RetS)
End Sub
二、带传入参数，带返回参数
- 写法1
Private Async Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
Dim t5 = Await WriteAllText(90000)
Me.Text = t5
End Sub
Public Async Function WriteAllText(ByVal mCount As Integer) As Task(Of String)
Return Await Task.Run(Function()
Return mWriteText(mCount)
End Function)
End Function
Public Function mWriteText(ByVal mCount As Integer) As String
Dim RetS As String = ""
For i As Integer = 0 To mCount
RetS += "iiiiiiiiii"
Next
File.WriteAllText("2.txt", RetS)
Return DateTime.Now.ToString("HH:mm:ss")
End Function
- 写法2
Private Async Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
Dim t4 As Task(Of String) = Task.Run(Function()
Return mWriteText(90000)
End Function)
Dim t5 As String = Await t4
Me.Text = t5
End Sub
Public Function mWriteText(ByVal mCount As Integer) As String
Dim RetS As String = ""
For i As Integer = 0 To mCount
RetS += "iiiiiiiiii"
Next
File.WriteAllText("2.txt", RetS)
Return DateTime.Now.ToString("HH:mm:ss")
End Function
- 写法3
Private Async Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
Dim t3 As Task(Of String) = Task.Run(Function()
Dim RetS As String = ""
For i As Integer = 0 To 90000
RetS += "iiiiiiiiii"
Next
File.WriteAllText("2.txt", RetS)
Return DateTime.Now.ToString("HH:mm:ss")
End Function)
Dim t5 As String = Await t3
Me.Text = t5
End Sub
三、多任务等待
Private Async Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
Dim tasks As New List(Of Task(Of String))()
Dim t1 As Task(Of String) = WriteAllText(10000)
tasks.Add(t1)
Dim t2 As Task(Of String) = WriteAllText(20000)
tasks.Add(t2)
Dim t3 As Task(Of String) = WriteAllText(30000)
tasks.Add(t3)
Dim kk() As String = Await Task.WhenAll(tasks)
Me.Text = kk(0) + "," + kk(1) + "," + kk(2)
End Sub
Public Async Function WriteAllText(ByVal mCount As Integer) As Task(Of String)
Return Task.Run(Function()
Return mWriteText(mCount)
End Function)
End Function
Public Function mWriteText(ByVal mCount As Integer) As String
Dim RetS As String = ""
For i As Integer = 0 To mCount
RetS += "iiiiiiiiii"
Next
File.WriteAllText("2.txt", RetS)
Return DateTime.Now.ToString("HH:mm:ss")
End Function
四、更新UI界面
Task.Run里面的函数是线程函数，直接更新会报错，下面使用IProgress(Of T)来辅助显示进度条
Dim progressT As IProgress(Of Integer)
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
progressT = New Progress(Of Integer)(AddressOf ProReport)
End Sub
Public Sub ProReport(ByVal i As Integer)
ProgressBar1.Value = i
End Sub
Private Async Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
Dim t3 As Task(Of String) = WriteAllText(30000, progressT)
Me.Text = Await t3
End Sub
Public Async Function WriteAllText(ByVal mCount As Integer, mprogressT As IProgress(Of Integer)) As Task(Of String)
Return Await Task.Run(Function()
Return mWriteText(mCount, mprogressT)
End Function)
End Function
Public Async Function mWriteText(ByVal mCount As Integer, mprogressT As IProgress(Of Integer)) As Task(Of String)
Dim RetS As String = ""
For i As Integer = 0 To mCount
RetS += "iiiiiiiiii"
Dim Precent As Integer = (i / mCount) * 100
Await Task.Delay(2000)
mprogressT.Report(Precent)
'ProgressBar1.Value = Precent
Next
File.WriteAllText("2.txt", RetS)
Return DateTime.Now.ToString("HH:mm:ss")
End Function
注：在Task.Run中，不建议用sleep函数来延时。建议使用Await Task.Delay(2000)
