click and doubleclick event in c# not working

Question

I have the following code in my C# application

The first determines what happens when the user double-clicks a picture.

 private void pictureDoubleClick(Object sender, EventArgs e)
        {
            PictureBox picture = (PictureBox)sender;
            Console.WriteLine(picture.ImageLocation);
            MessageBox.Show("Test");
        }

And another one for single click:

private void picutureClick(Object sender, EventArgs e)
        {
            PictureBox picture = (PictureBox)sender;

            if (picture.BorderStyle == BorderStyle.None)
            {
                picture.BorderStyle = BorderStyle.Fixed3D;
                picture.BackColor = Color.Red;
            }
            else
            {
                picture.BorderStyle = BorderStyle.None;
                picture.BackColor = Color.White;
            }
        }

I've called both the functions like so:

box.Click += new System.EventHandler(this.picutureClick);
box.DoubleClick += new System.EventHandler(this.pictureDoubleClick);

However I'm facing a strange bug, the DoubleClick event won't get activated, the only way to make it work is if I comment out the single click. The single click works whether or not I comment or un-comment the Doubleclick event. I looked around for solutions but I couldn't find any that resolved my issue.

nevets · Accepted Answer

It's a weird behavior, that changing BorderStyle of a picture box will stop the click to propagate (a Click event will always raise before DoubleClick event).

I do not really know how to handle it properly, but we could do some hack to make the feature work. We can introduce a "lag" between a Click and DoubleClick to make the DoubleClick is checked before Click.

Here we use a Timer to do the job:

private Timer _timer;
private PictureBox _sender;
private int _clicks;

public Form1()
{
    InitializeComponent();

    pictureBox.Click += picutureClick;
    pictureBox.DoubleClick += (s, e) =>
                                    {
                                        // do your double click handling

                                        _clicks = 0;
                                    };

    // this Interval comes from trail and error, it's a balance between lag and  
    // correctness. To play safe, you can use SystemInformation.DoubleClickTime,
    // but may introduce a bit long lagging after you click and before you
    // see the effects.
    _timer = new Timer {Interval = 75}; 
    _timer.Tick += (s, e) =>
                        {
                            if (_clicks < 2)
                            {
                                ClickHandler(_sender);
                            }

                            _clicks = 0;

                            _timer.Stop();
                        };
}

private void picutureClick(Object sender, EventArgs e)
{
    _clicks++;
    _sender = (PictureBox) sender;

    if (_clicks == 1)
    {
        _timer.Start();
    }
}

private void ClickHandler(PictureBox picture)
{
    if (picture.BorderStyle == BorderStyle.None)
    {
        // this line is not thread safe, but you could comment out the .InvokeIfRequire()
        // and uncomment this line to have a look at your form's behavior
        //picture.BorderStyle = BorderStyle.Fixed3D;
        picture.InvokeIfRequired(c => (c as PictureBox).BorderStyle = BorderStyle.Fixed3D);
        picture.BackColor = Color.Red;
    }
    else
    {
        // same for this
        //picture.BorderStyle = BorderStyle.Fixed3D;
        picture.InvokeIfRequired(c => (c as PictureBox).BorderStyle = BorderStyle.None);
        picture.BackColor = Color.White;
    }
}

In the above code, I used an extension method to handle cross-thread property updating:

public static void InvokeIfRequired(this Control c, Action action)
{
    if (c.InvokeRequired)
    {
        c.Invoke(new Action(() => action(c)));
    }
    else
    {
        action(c);
    }
}

Edit:

The extension method I used above is to simplify the code written to do cross-thread property update. More details on this topic can be found here: Automating the InvokeRequired code pattern

Here are some details on Extension Method:

An extension method only works if it's declared in a non-generic, non-nested static class. To make it work, you need to declare a new public static class to hold the method.

// your form class declared here
public partial class Form1 : Form
{
    // code omitted here
}

// declare the extension method in this extension class
public static class ControlExtensions
{
    public static void InvokeIfRequired(this Control c, Action action)
    {
        if (c.InvokeRequired)
        {
            c.Invoke(new Action(() => action(c)));
        }
        else
        {
            action(c);
        }
    }
}

click and doubleclick event in c# not working

Answers (2)

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