Application::Run Method (ApplicationContext^)

 

Begins running a standard application message loop on the current thread, with an ApplicationContext.

Namespace:   System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)

public:
static void Run(
	ApplicationContext^ context
)

Parameters

context
Type: System.Windows.Forms::ApplicationContext^

An ApplicationContext in which the application is run.

Exception Condition
InvalidOperationException

A main message loop is already running on this thread.

The message loop runs until Exit or ExitThread is called or the ThreadExit event is raised on the context object.

The 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.

The code for the AppForm1 and AppForm2 forms is not shown for the purpose of brevity. See the ApplicationContext class overview for the whole code listing.

// 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;
      }
   }

};


.NET Framework
Available since 1.1
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