ApplicationContext Class
Important
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Specifies the contextual information about an application thread.
public ref class ApplicationContext
public ref class ApplicationContext : IDisposable
public class ApplicationContext
public class ApplicationContext : IDisposable
type ApplicationContext = class
type ApplicationContext = class
interface IDisposable
Public Class ApplicationContext
Public Class ApplicationContext
Implements IDisposable
- Inheritance
-
ApplicationContext
- Implements
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 ApplicationContext, along with the Application.Run(context)
method, to display multiple forms when the application starts.
The class MyApplicationContext
inherits from ApplicationContext 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 ApplicationContext.
#using <System.dll>
#using <System.Drawing.dll>
#using <System.Windows.Forms.dll>
using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;
using namespace System::ComponentModel;
using namespace System::Text;
using namespace System::IO;
// A simple form that represents a window in our application
public ref class AppForm2: public System::Windows::Forms::Form
{
public:
AppForm2()
{
this->Size = System::Drawing::Size( 300, 300 );
this->Text = "AppForm2";
}
};
// A simple form that represents a window in our application
public ref class AppForm1: public System::Windows::Forms::Form
{
public:
AppForm1()
{
this->Size = System::Drawing::Size( 300, 300 );
this->Text = "AppForm1";
}
};
// The class that handles the creation of the application windows
ref class MyApplicationContext: public ApplicationContext
{
private:
int _formCount;
AppForm1^ _form1;
AppForm2^ _form2;
System::Drawing::Rectangle _form1Position;
System::Drawing::Rectangle _form2Position;
FileStream^ _userData;
public:
MyApplicationContext()
{
_formCount = 0;
// Handle the ApplicationExit event to know when the application is exiting.
Application::ApplicationExit += gcnew EventHandler( this, &MyApplicationContext::OnApplicationExit );
try
{
// Create a file that the application will store user specific data in.
_userData = gcnew FileStream( String::Concat( Application::UserAppDataPath, "\\appdata.txt" ),FileMode::OpenOrCreate );
}
catch ( IOException^ e )
{
// Inform the user that an error occurred.
MessageBox::Show( "An error occurred while attempting to show the application. The error is: {0}", dynamic_cast<String^>(e) );
// Exit the current thread instead of showing the windows.
ExitThread();
}
// Create both application forms and handle the Closed event
// to know when both forms are closed.
_form1 = gcnew AppForm1;
_form1->Closed += gcnew EventHandler( this, &MyApplicationContext::OnFormClosed );
_form1->Closing += gcnew CancelEventHandler( this, &MyApplicationContext::OnFormClosing );
_formCount++;
_form2 = gcnew AppForm2;
_form2->Closed += gcnew EventHandler( this, &MyApplicationContext::OnFormClosed );
_form2->Closing += gcnew CancelEventHandler( this, &MyApplicationContext::OnFormClosing );
_formCount++;
// Get the form positions based upon the user specific data.
if ( ReadFormDataFromFile() )
{
// 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;
}
// Show both forms.
_form1->Show();
_form2->Show();
}
void OnApplicationExit( Object^ /*sender*/, EventArgs^ /*e*/ )
{
// 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 ( Exception^ )
{
}
}
private:
void OnFormClosing( Object^ sender, CancelEventArgs^ /*e*/ )
{
// When a form is closing, remember the form position so it
// can be saved in the user data file.
if ( dynamic_cast<AppForm1^>(sender) != nullptr )
_form1Position = (dynamic_cast<Form^>(sender))->Bounds;
else
if ( dynamic_cast<AppForm1^>(sender) != nullptr )
_form2Position = (dynamic_cast<Form^>(sender))->Bounds;
}
void OnFormClosed( Object^ /*sender*/, EventArgs^ /*e*/ )
{
// When a form is closed, decrement the count of open forms.
// When the count gets to 0, exit the app by calling
// ExitThread().
_formCount--;
if ( _formCount == 0 )
{
ExitThread();
}
}
bool WriteFormDataToFile()
{
// Write the form positions to the file.
UTF8Encoding^ encoding = gcnew UTF8Encoding;
RectangleConverter^ rectConv = gcnew RectangleConverter;
String^ form1pos = rectConv->ConvertToString( _form1Position );
String^ form2pos = rectConv->ConvertToString( _form2Position );
array<Byte>^dataToWrite = encoding->GetBytes( String::Concat( "~", 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 ( Exception^ )
{
// An error occurred while attempting to write, return false.
return false;
}
}
bool ReadFormDataFromFile()
{
// Read the form positions from the file.
UTF8Encoding^ encoding = gcnew UTF8Encoding;
String^ data;
if ( _userData->Length != 0 )
{
array<Byte>^dataToRead = gcnew array<Byte>(_userData->Length);
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 ( IOException^ e )
{
String^ errorInfo = dynamic_cast<String^>(e);
// An error occurred while attempt to read, return false.
return false;
}
// Parse out the data to get the window rectangles
data = encoding->GetString( dataToRead );
try
{
// Convert the String* data to rectangles
RectangleConverter^ rectConv = gcnew RectangleConverter;
String^ form1pos = data->Substring( 1, data->IndexOf( "~", 1 ) - 1 );
_form1Position = *safe_cast<Rectangle^>(rectConv->ConvertFromString( form1pos ));
String^ form2pos = data->Substring( data->IndexOf( "~", 1 ) + 1 );
_form2Position = *safe_cast<Rectangle^>(rectConv->ConvertFromString( form2pos ));
return true;
}
catch ( Exception^ )
{
// Error occurred while attempting to convert the rectangle data.
// Return false to use default values.
return false;
}
}
else
{
// No data in the file, return false to use default values.
return false;
}
}
};
[STAThread]
int main()
{
// Create the MyApplicationContext, that derives from ApplicationContext,
// that manages when the application should exit.
MyApplicationContext^ context = gcnew MyApplicationContext;
// Run the application with the specific context. It will exit when
// all forms are closed.
Application::Run( context );
}
using System;
using System.Drawing;
using System.Windows.Forms;
using System.ComponentModel;
using System.Text;
using System.IO;
namespace MyApplication
{
// A simple form that represents a window in our application
public class AppForm2 : System.Windows.Forms.Form
{
public AppForm2()
{
this.Size = new System.Drawing.Size(300, 300);
this.Text = "AppForm2";
}
}
// A simple form that represents a window in our application
public class AppForm1 : System.Windows.Forms.Form
{
public AppForm1()
{
this.Size = new System.Drawing.Size(300, 300);
this.Text = "AppForm1";
}
}
// The class that handles the creation of the application windows
class MyApplicationContext : ApplicationContext
{
private int _formCount;
private AppForm1 _form1;
private AppForm2 _form2;
private Rectangle _form1Position;
private Rectangle _form2Position;
private FileStream _userData;
private MyApplicationContext()
{
_formCount = 0;
// Handle the ApplicationExit event to know when the application is exiting.
Application.ApplicationExit += new EventHandler(this.OnApplicationExit);
try
{
// Create a file that the application will store user specific data in.
_userData = new FileStream(Application.UserAppDataPath + "\\appdata.txt", FileMode.OpenOrCreate);
}
catch (IOException e)
{
// 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();
}
// Create both application forms and handle the Closed event
// to know when both forms are closed.
_form1 = new AppForm1();
_form1.Closed += new EventHandler(OnFormClosed);
_form1.Closing += new CancelEventHandler(OnFormClosing);
_formCount++;
_form2 = new AppForm2();
_form2.Closed += new EventHandler(OnFormClosed);
_form2.Closing += new CancelEventHandler(OnFormClosing);
_formCount++;
// Get the form positions based upon the user specific data.
if (ReadFormDataFromFile())
{
// 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;
}
// Show both forms.
_form1.Show();
_form2.Show();
}
private void OnApplicationExit(object sender, EventArgs e)
{
// 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 { }
}
private void OnFormClosing(object sender, CancelEventArgs e)
{
// When a form is closing, remember the form position so it
// can be saved in the user data file.
if (sender is AppForm1)
_form1Position = ((Form)sender).Bounds;
else if (sender is AppForm2)
_form2Position = ((Form)sender).Bounds;
}
private void OnFormClosed(object sender, EventArgs e)
{
// When a form is closed, decrement the count of open forms.
// When the count gets to 0, exit the app by calling
// ExitThread().
_formCount--;
if (_formCount == 0)
{
ExitThread();
}
}
private bool WriteFormDataToFile()
{
// Write the form positions to the file.
UTF8Encoding encoding = new UTF8Encoding();
RectangleConverter rectConv = new RectangleConverter();
string form1pos = rectConv.ConvertToString(_form1Position);
string form2pos = rectConv.ConvertToString(_form2Position);
byte[] dataToWrite = 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;
}
}
private bool ReadFormDataFromFile()
{
// Read the form positions from the file.
UTF8Encoding encoding = new UTF8Encoding();
string data;
if (_userData.Length != 0)
{
byte[] dataToRead = new byte[_userData.Length];
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 (IOException e)
{
string errorInfo = e.ToString();
// An error occurred while attempt to read, return false.
return false;
}
// Parse out the data to get the window rectangles
data = encoding.GetString(dataToRead);
try
{
// Convert the string data to rectangles
RectangleConverter rectConv = new RectangleConverter();
string form1pos = data.Substring(1, data.IndexOf("~", 1) - 1);
_form1Position = (Rectangle)rectConv.ConvertFromString(form1pos);
string form2pos = data.Substring(data.IndexOf("~", 1) + 1);
_form2Position = (Rectangle)rectConv.ConvertFromString(form2pos);
return true;
}
catch
{
// Error occurred while attempting to convert the rectangle data.
// Return false to use default values.
return false;
}
}
else
{
// No data in the file, return false to use default values.
return false;
}
}
[STAThread]
static void Main(string[] args)
{
// Create the MyApplicationContext, that derives from ApplicationContext,
// that manages when the application should exit.
MyApplicationContext context = new MyApplicationContext();
// Run the application with the specific context. It will exit when
// all forms are closed.
Application.Run(context);
}
}
}
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
You can use the ApplicationContext class to redefine the circumstances that cause a message loop to exit. By default, the ApplicationContext listens to the Closed event on the application's main Form, then exits the thread's message loop.
Application |
Initializes a new instance of the ApplicationContext class with no context. |
Application |
Initializes a new instance of the ApplicationContext class with the specified Form. |
Main |
Gets or sets the Form to use as context. |
Tag |
Gets or sets an object that contains data about the control. |
Dispose() |
Releases all resources used by the ApplicationContext. |
Dispose(Boolean) |
Releases the unmanaged resources used by the ApplicationContext and optionally releases the managed resources. |
Equals(Object) |
Determines whether the specified object is equal to the current object. (Inherited from Object) |
Exit |
Terminates the message loop of the thread. |
Exit |
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. |
Get |
Serves as the default hash function. (Inherited from Object) |
Get |
Gets the Type of the current instance. (Inherited from Object) |
Memberwise |
Creates a shallow copy of the current Object. (Inherited from Object) |
On |
Calls ExitThreadCore(), which raises the ThreadExit event. |
To |
Returns a string that represents the current object. (Inherited from Object) |
Thread |
Occurs when the message loop of the thread should be terminated, by calling ExitThread(). |
Продукт | Версії |
---|---|
.NET Framework | 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
Windows Desktop | 3.0, 3.1, 5, 6, 7, 8, 9 |
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