Timer.SynchronizingObject Property


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Gets or sets the object used to marshal event-handler calls that are issued when an interval has elapsed.

Namespace:   System.Timers
Assembly:  System (in System.dll)

public ISynchronizeInvoke SynchronizingObject { get; set; }

Property Value

Type: System.ComponentModel.ISynchronizeInvoke

The ISynchronizeInvoke representing the object used to marshal the event-handler calls that are issued when an interval has elapsed. The default is null.

When SynchronizingObject is null, the method that handles the Elapsed event is called on a thread from the system-thread pool. For more information on system-thread pools, see ThreadPool.

When the Elapsed event is handled by a visual Windows Forms component, such as a button, accessing the component through the system-thread pool might result in an exception or just might not work. Avoid this effect by setting SynchronizingObject to a Windows Forms component, which causes the method that handles the Elapsed event to be called on the same thread that the component was created on.


Even if the SynchronizingObject property is not null, Elapsed events can occur after the Dispose or Stop method has been called or after the Enabled property has been set to false, because the signal to raise the Elapsed event is always queued for execution on a thread pool thread. One way to resolve this race condition is to set a flag that tells the event handler for the Elapsed event to ignore subsequent events.

If the Timer is used inside Visual Studio in a Windows Forms designer, SynchronizingObject is automatically set to the control that contains the Timer. For example, if you place a Timer on a designer for Form1 (which inherits from Form), the SynchronizingObject property of Timer is set to the instance of Form1.

The following example is a Windows Forms app that serves as a very simple text file editor. When the text in the text box has not been saved, the app asks the user at one-minute intervals whether he or she wants to save the contents of the text box. To do this, the Interval property is set to one minute (60,000 milliseconds), and the SynchronizingObject property is set to the Form object.

using System;
using System.IO;
using  Timers = System.Timers;
using System.Windows.Forms;
public partial class Form1 : Form
    Timers.Timer timer = null;
    StreamWriter sw = null;
    bool hasChanged = false;
    bool dialogIsOpen = false;
    int elapsedMinutes = 0;
    // Cache the text box cache internally without saving it.
    String txt = "";

    public Form1()

        this.Text = "Quick Text Editor";
        button1.Text = "Save";
        textBox1.Multiline = true;

        // Configure the SaveFile dialog
        saveFileDialog1.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*";
        saveFileDialog1.RestoreDirectory = true;

        // Create a timer with a 1-minute interval
        timer = new Timers.Timer(60000);
        // Define the event handler
        timer.Elapsed += this.PromptForSave;
        // Synchronize the timer with the text box
        timer.SynchronizingObject = this;
        // Start the timer
        timer.AutoReset = true;

    private void PromptForSave(Object source, Timers.ElapsedEventArgs e)
        if (hasChanged & (!dialogIsOpen)) {
            dialogIsOpen = true;
            if (MessageBox.Show(String.Format("{0} minutes have elapsed since the text was saved. Save it now? ",
                elapsedMinutes), "Save Text",
                MessageBoxButtons.YesNoCancel, MessageBoxIcon.Question) == DialogResult.Yes)
                button1_Click(this, EventArgs.Empty);
                dialogIsOpen = false;

    private void button1_Click(Object sender, EventArgs e)
        if (String.IsNullOrEmpty(saveFileDialog1.FileName)) {
            if (saveFileDialog1.ShowDialog() == DialogResult.OK)
                sw = new StreamWriter(saveFileDialog1.FileName, false);
        txt = textBox1.Text;
        hasChanged = false;

    private void form1_FormClosing(Object sender, FormClosingEventArgs e)
        if (sw != null) {

    private void textBox1_TextChanged(Object sender, EventArgs e)
        hasChanged = true;


The example requires that you add the following controls to the form:

  • A TextBox control named TextBox1 (its default name).

  • A Button control named Button1 (its default name).

  • A SaveFileDialog control named SaveSaveFileDialog1 (its default name) .

.NET Framework
Available since 1.1
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