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How to distinguish between clicks and double-clicks (Windows Forms .NET)

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Typically, a single click initiates a user interface action and a double-click extends the action. For example, one click usually selects an item, and a double-click edits the selected item. However, the Windows Forms click events do not easily accommodate a scenario where a click and a double-click perform incompatible actions, because an action tied to the Click or MouseClick event is performed before the action tied to the DoubleClick or MouseDoubleClick event. This topic demonstrates two solutions to this problem.

One solution is to handle the double-click event and roll back the actions in the handling of the click event. In rare situations you may need to simulate click and double-click behavior by handling the MouseDown event and by using the DoubleClickTime and DoubleClickSize properties of the SystemInformation class. You measure the time between clicks and if a second click occurs before the value of DoubleClickTime is reached and the click is within a rectangle defined by DoubleClickSize, perform the double-click action; otherwise, perform the click action.

To roll back a click action

Ensure that the control you are working with has standard double-click behavior. If not, enable the control with the SetStyle method. Handle the double-click event and roll back the click action as well as the double-click action. The following code example demonstrates a how to create a custom button with double-click enabled, as well as how to roll back the click action in the double-click event handling code.

This code example uses a new button control that enables double-clicks:

public partial class DoubleClickButton : Button
{
    public DoubleClickButton()
    {
        // Set the style so a double click event occurs.
        SetStyle(ControlStyles.StandardClick | ControlStyles.StandardDoubleClick, true);
    }
}

Public Class DoubleClickButton : Inherits Button

    Public Sub New()
        SetStyle(ControlStyles.StandardClick Or ControlStyles.StandardDoubleClick, True)
    End Sub

End Class

The following code demonstrates how a form changes the style of border based on a click or double-click of the new button control:

public partial class Form1 : Form
{
    private FormBorderStyle _initialStyle;
    private bool _isDoubleClicking;

    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        _initialStyle = this.FormBorderStyle;

        var button1 = new DoubleClickButton();
        button1.Location = new Point(50, 50);
        button1.Size = new Size(200, 23);
        button1.Text = "Click or Double Click";
        button1.Click += Button1_Click;
        button1.DoubleClick += Button1_DoubleClick;

        Controls.Add(button1);
    }

    private void Button1_DoubleClick(object sender, EventArgs e)
    {
        // This flag prevents the click handler logic from running
        // A double click raises the click event twice.
        _isDoubleClicking = true;
        FormBorderStyle = _initialStyle;
    }

    private void Button1_Click(object sender, EventArgs e)
    {
        if (_isDoubleClicking)
            _isDoubleClicking = false;
        else
            FormBorderStyle = FormBorderStyle.FixedToolWindow;
    }
}

Partial Public Class Form1

    Private _initialStyle As FormBorderStyle
    Private _isDoubleClicking As Boolean

    Public Sub New()
        InitializeComponent()
    End Sub

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Dim button1 As New DoubleClickButton

        _initialStyle = FormBorderStyle

        button1.Location = New Point(50, 50)
        button1.Size = New Size(200, 23)
        button1.Text = "Click or Double Click"

        AddHandler button1.Click, AddressOf Button1_Click
        AddHandler button1.DoubleClick, AddressOf Button1_DoubleClick

        Controls.Add(button1)

    End Sub

    Private Sub Button1_DoubleClick(sender As Object, e As EventArgs)
        ' This flag prevents the click handler logic from running
        ' A double click raises the click event twice.
        _isDoubleClicking = True
        FormBorderStyle = _initialStyle
    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs)
        If _isDoubleClicking Then
            _isDoubleClicking = False
        Else
            FormBorderStyle = FormBorderStyle.FixedToolWindow
        End If
    End Sub
End Class

To distinguish between clicks

Handle the MouseDown event and determine the location and time span between clicks using the SystemInformation property and a Timer component. Perform the appropriate action depending on whether a click or double-click takes place. The following code example demonstrates how this can be done.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Windows.Forms;

namespace project
{
    public partial class Form2 : Form
    {
        private DateTime _lastClick;
        private bool _inDoubleClick;
        private Rectangle _doubleClickArea;
        private TimeSpan _doubleClickMaxTime;
        private Action _doubleClickAction;
        private Action _singleClickAction;
        private Timer _clickTimer;

        public Form2()
        {
            InitializeComponent();
            _doubleClickMaxTime = TimeSpan.FromMilliseconds(SystemInformation.DoubleClickTime);

            _clickTimer = new Timer();
            _clickTimer.Interval = SystemInformation.DoubleClickTime;
            _clickTimer.Tick += ClickTimer_Tick;

            _singleClickAction = () => MessageBox.Show("Single clicked");
            _doubleClickAction = () => MessageBox.Show("Double clicked");
        }

        private void Form2_MouseDown(object sender, MouseEventArgs e)
        {
            if (_inDoubleClick)
            {
                _inDoubleClick = false;

                TimeSpan length = DateTime.Now - _lastClick;

                // If double click is valid, respond
                if (_doubleClickArea.Contains(e.Location) && length < _doubleClickMaxTime)
                {
                    _clickTimer.Stop();
                    _doubleClickAction();
                }

                return;
            }

            // Double click was invalid, restart 
            _clickTimer.Stop();
            _clickTimer.Start();
            _lastClick = DateTime.Now;
            _inDoubleClick = true;
            _doubleClickArea = new Rectangle(e.Location - (SystemInformation.DoubleClickSize / 2), 
                                             SystemInformation.DoubleClickSize);
        }

        private void ClickTimer_Tick(object sender, EventArgs e)
        {
            // Clear double click watcher and timer
            _inDoubleClick = false;
            _clickTimer.Stop();

            _singleClickAction();
        }
    }
}

Imports System.Drawing
Imports System.Windows.Forms

Public Class Form2
    Private _lastClick As Date
    Private _inDoubleClick As Boolean
    Private _doubleClickArea As Rectangle
    Private _doubleClickMaxTime As TimeSpan
    Private _singleClickAction As Action
    Private _doubleClickAction As Action
    Private WithEvents _clickTimer As Timer

    Private Sub Form2_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        _doubleClickMaxTime = TimeSpan.FromMilliseconds(SystemInformation.DoubleClickTime)

        _clickTimer = New Timer()
        _clickTimer.Interval = SystemInformation.DoubleClickTime

        _singleClickAction = Sub()
                                 MessageBox.Show("Single click")
                             End Sub

        _doubleClickAction = Sub()
                                 MessageBox.Show("Double click")
                             End Sub
    End Sub

    Private Sub Form2_MouseDown(sender As Object, e As MouseEventArgs) Handles MyBase.MouseDown
        If _inDoubleClick Then

            _inDoubleClick = False

            Dim length As TimeSpan = Date.Now - _lastClick

            ' If double click is valid, respond
            If _doubleClickArea.Contains(e.Location) And length < _doubleClickMaxTime Then
                _clickTimer.Stop()
                Call _doubleClickAction()
            End If

            Return
        End If

        ' Double click was invalid, restart 
        _clickTimer.Stop()
        _clickTimer.Start()
        _lastClick = Date.Now
        _inDoubleClick = True
        _doubleClickArea = New Rectangle(e.Location - (SystemInformation.DoubleClickSize / 2),
                                         SystemInformation.DoubleClickSize)
    End Sub

    Private Sub SingleClickTimer_Tick(sender As Object, e As EventArgs) Handles _clickTimer.Tick
        ' Clear double click watcher and timer
        _inDoubleClick = False
        _clickTimer.Stop()

        Call _singleClickAction()
    End Sub

End Class

See also