Application.Run Method (ApplicationContext)


The .NET API Reference documentation has a new home. Visit the .NET API Browser on to see the new experience.

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


Type: System.Windows.Forms.ApplicationContext

An ApplicationContext in which the application is run.

Exception Condition

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
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.

        // 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);            

        form2 = new AppForm2();
        form2.Closed += new EventHandler(OnFormClosed);            
        form2.Closing += new CancelEventHandler(OnFormClosing);            

        // 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.

    private void OnApplicationExit(object sender, EventArgs e) {
        // When the application is exiting, write the application data to the
        // user file and close it.

        try {
            // Ignore any errors that might occur while closing the file handle.
        } 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().
        if (formCount == 0) {

    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.Write(dataToWrite, 0, 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;

    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.


.NET Framework
Available since 1.1
Return to top