Is there an event for an image change for a PictureBox Control?

Question

How do I know when the image of the picturebox change?
Is there an event for an image change?

Answer 1

The Paint event is working:

private void pictureBox_Paint(object sender, PaintEventArgs e)
{
    // image has changed
}

Answer 2

There are load events if you use Load() or LoadAsync(), but not for the Image property. This is explicitly set by you (the developer) and is generally speaking in 100% of your control (see notation below). If you really wanted to though (there isn't really a point, though), you can derive your own UserControl from PictureBox and override the Image property, and implement your own event handler.

Notation I suppose one event you would want an event to subscribe to is if you are using some third-party component or control that changes the image property, and you want to implement some sort of sub routine when this happens. In this event it would be a reason to need a ImageChanged event since you don't have control over when the image is set. Unfortunately there still isn't a way to circumvent this scenario.

Answer 3

using System;
using System.Windows.Forms;
using System.Drawing;

namespace CustomPX
{
    public class CustomPictureBox : PictureBox
    {
        public event EventHandler ImageChanged;
        public Image Image
        {
            get
            {
                return base.Image;
            }
            set
            {
                base.Image = value;
                if (this.ImageChanged != null)
                    this.ImageChanged(this, new EventArgs());
            }
        }
    }
}

You can add this Class into ToolBox and/or from code and use ImageChanged event to catch if Image is Changed

Answer 4

First make sure that the images are loaded asynchronously. To do this set the PictureBox's WaitOnLoad property to false (which is the default value).

pictureBox1.WaitOnLoad = false;

Then load the image asynchronously:

pictureBox1.LoadAsync("neutrinos.gif");

Create an event handler for the PictureBox's LoadCompleted event. This event is triggered when the asynchronous image-load operation is completed, canceled, or caused an exception.

pictureBox1.LoadCompleted += PictureBox1_LoadCompleted;

private void PictureBox1_LoadCompleted(Object sender, AsyncCompletedEventArgs e) 
{       
    //...       
}

You can find more information about this event on MSDN:

http://msdn.microsoft.com/en-us/library/system.windows.forms.picturebox.loadcompleted.aspx