Specifies the contextual information about an application thread.
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
Thetype exposes the following members.
|Dispose||Releases all resources used by the .|
|Dispose(Boolean)||Releases the unmanaged resources used by the and optionally releases the managed resources.|
|Equals(Object)||Determines whether the specified object is equal to the current object. (Inherited from Object.)|
|ExitThread||Terminates the message loop of the thread.|
|ExitThreadCore||Terminates the message loop of the thread.|
|Finalize||Attempts to free resources and perform other cleanup operations before the application context is reclaimed by garbage collection. (Overrides Object.Finalize.)|
|GetHashCode||Serves as the default hash function. (Inherited from Object.)|
|GetType||Gets the Type of the current instance. (Inherited from Object.)|
|MemberwiseClone||Creates a shallow copy of the current Object. (Inherited from Object.)|
|OnMainFormClosed||Calls ExitThreadCore, which raises the ThreadExit event.|
|ToString||Returns a string that represents the current object. (Inherited from Object.)|
The following code example displays two forms and exits the application when both forms are closed. When the application starts and exits, the position of each form is remembered. This example demonstrates how to use an , along with the Application.Run(context) method, to display multiple forms when the application starts.
The class MyApplicationContext inherits from and keeps track when each form is closed, and exits the current thread when they both are. The class stores the positions of each form for the user. The form position data is stored in a file titled Appdata.txt that is created in the location determined by UserAppDataPath.
The Main method calls Application.Run(context) to start the application, given the .
Imports System Imports System.Drawing Imports System.Windows.Forms Imports System.ComponentModel Imports System.Text Imports System.IO ' A simple form that represents a window in our application Public Class AppForm1 Inherits System.Windows.Forms.Form Public Sub New() MyBase.New() Me.Size = New System.Drawing.Size(300, 300) Me.Text = "AppForm1" End Sub End Class ' A simple form that represents a window in our application Public Class AppForm2 Inherits System.Windows.Forms.Form Public Sub New() MyBase.New() Me.Size = New System.Drawing.Size(300, 300) Me.Text = "AppForm2" End Sub End Class ' The class that handles the creation of the application windows Public Class MyApplicationContext Inherits ApplicationContext Private formCount As Integer Private form1 As AppForm1 Private form2 As AppForm2 Private form1Position As Rectangle Private form2Position As Rectangle Private userData As FileStream Public Sub New() MyBase.New() formCount = 0 ' Handle the ApplicationExit event to know when the application is exiting. AddHandler Application.ApplicationExit, AddressOf OnApplicationExit Try ' Create a file that the application will store user specific data in. userData = New FileStream(Application.UserAppDataPath + "\appdata.txt", FileMode.OpenOrCreate) Catch e As IOException ' Inform the user that an error occurred. MessageBox.Show("An error occurred while attempting to show the application." + _ "The error is:" + e.ToString()) ' Exit the current thread instead of showing the windows. ExitThread() End Try ' Create both application forms and handle the Closed event ' to know when both forms are closed. form1 = New AppForm1() AddHandler form1.Closed, AddressOf OnFormClosed AddHandler form1.Closing, AddressOf OnFormClosing formCount = formCount + 1 form2 = New AppForm2() AddHandler form2.Closed, AddressOf OnFormClosed AddHandler form2.Closing, AddressOf OnFormClosing formCount = formCount + 1 ' Get the form positions based upon the user specific data. If (ReadFormDataFromFile()) Then ' If the data was read from the file, set the form ' positions manually. form1.StartPosition = FormStartPosition.Manual form2.StartPosition = FormStartPosition.Manual form1.Bounds = form1Position form2.Bounds = form2Position End If ' Show both forms. form1.Show() form2.Show() End Sub Private Sub OnApplicationExit(ByVal sender As Object, ByVal e As EventArgs) ' When the application is exiting, write the application data to the ' user file and close it. WriteFormDataToFile() Try ' Ignore any errors that might occur while closing the file handle. userData.Close() Catch End Try End Sub Private Sub OnFormClosing(ByVal sender As Object, ByVal e As CancelEventArgs) ' When a form is closing, remember the form position so it ' can be saved in the user data file. If TypeOf sender Is AppForm1 Then form1Position = CType(sender, Form).Bounds ElseIf TypeOf sender Is AppForm2 Then form2Position = CType(sender, Form).Bounds End If End Sub Private Sub OnFormClosed(ByVal sender As Object, ByVal e As EventArgs) ' When a form is closed, decrement the count of open forms. ' When the count gets to 0, exit the app by calling ' ExitThread(). formCount = formCount - 1 If (formCount = 0) Then ExitThread() End If End Sub Private Function WriteFormDataToFile() As Boolean ' Write the form positions to the file. Dim encoding As UTF8Encoding = New UTF8Encoding() Dim rectConv As RectangleConverter = New RectangleConverter() Dim form1pos As String = rectConv.ConvertToString(form1Position) Dim form2pos As String = rectConv.ConvertToString(form2Position) Dim dataToWrite As Byte() = encoding.GetBytes("~" + form1pos + "~" + form2pos) Try ' Set the write position to the start of the file and write userData.Seek(0, SeekOrigin.Begin) userData.Write(dataToWrite, 0, dataToWrite.Length) userData.Flush() userData.SetLength(dataToWrite.Length) Return True Catch ' An error occurred while attempting to write, return false. Return False End Try End Function Private Function ReadFormDataFromFile() As Boolean ' Read the form positions from the file. Dim encoding As UTF8Encoding = New UTF8Encoding() Dim data As String If (userData.Length <> 0) Then Dim dataToRead(userData.Length) As Byte Try ' Set the read position to the start of the file and read. userData.Seek(0, SeekOrigin.Begin) userData.Read(dataToRead, 0, dataToRead.Length) Catch e As IOException Dim errorInfo As String = e.ToString() ' An error occurred while attempt to read, return false. Return False End Try ' Parse out the data to get the window rectangles data = encoding.GetString(dataToRead) Try ' Convert the string data to rectangles Dim rectConv As RectangleConverter = New RectangleConverter() Dim form1pos As String = data.Substring(1, data.IndexOf("~", 1) - 1) form1Position = CType(rectConv.ConvertFromString(form1pos), Rectangle) Dim form2pos As String = data.Substring(data.IndexOf("~", 1) + 1) form2Position = CType(rectConv.ConvertFromString(form2pos), Rectangle) Return True Catch ' Error occurred while attempting to convert the rectangle data. ' Return false to use default values. Return False End Try Else ' No data in the file, return false to use default values. Return False End If End Function End Class Public Module MyApplication Public Sub Main() ' Create the MyApplicationContext, that derives from ApplicationContext, ' that manages when the application should exit. Dim context As MyApplicationContext = New MyApplicationContext() ' Run the application with the specific context. It will exit when ' all forms are closed. Application.Run(context) End Sub End Module
Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.