• 0

[C#] Dynamic Event Handling


Question

I have an arbitrary list of elements that I'm adding to a tableLayoutPanel (it was the first layout I came across that I could add elements to and it would be scrollable). For each element, I add the name of the element, with a TrackBar and a TextBox. (so three controls per row).

I want to link the TrackBar with the TextBox in a way where when I move the TrackBar, it changes the numeric value in the textBox to the value of the TrackBar (and ViceVersa).

I know how to add the Events for the two (+= new EventHandler(Scrolled)). The problem is all my elements are being added with the same EventName, so no matter which control I manipulate, i want the corresponding controls to change as well... I think this is OK, because I don't know how many of these elements I will have until runtime.

My question is this... inside the Scrolled method, how can I make elementScrollBar1 change elementTextBox1, and 2 -> 2, 3 -> 3, etc? The only things passed in are object sender, EventArgs events. Is what I'm trying to do possible? If so please help.

Link to comment
https://www.neowin.net/forum/topic/610910-c-dynamic-event-handling/
Share on other sites

21 answers to this question

Recommended Posts

  • 0

You need something like this:

		private void AddControls_Click(object sender, EventArgs e)
		{
			TextBox textbox = new TextBox();
			TrackBar trackbar = new TrackBar();
			trackbar.Maximum = 10;
			trackbar.Tag = textbox;

			trackbar.Scroll +=  delegate(object sender2, EventArgs e2)
								{
									TrackBar currentTrackBar = sender2 as TrackBar;
									TextBox currentTextBox = currentTrackBar.Tag as TextBox;
									currentTextBox.Text = currentTrackBar.Value.ToString();
								};
			tableLayoutPanel1.Controls.AddRange(new Control[] { textbox, trackbar });

		}

Add that into a button click event.

Hope this helps.

  • 0

My controls are added dynamically when the program is run, not by a click event... I'm guessing replacing my code with this for those two controls will have the same effect? Looking at this it seems like I should do this for other trackbar/textbox combos I have... this links the two I'm guessing?

Does this also allow someone to edit the textbox and it affect the trackbar?

  • 0

I figured out that it doesn't and modified my code to make it work.. I did something similar to what you showed, using the textBox.Tag = trackBar to put a reference.

Is this common practice? If I want to relate two controls, should I just reference each within the Tag variable? Is that common practice? It seems a little odd to me, even though it works as a hack.

  • 0

Why don't you create a custom control that includes the elements you need, and put the logic there? That's probably the most common practice in this case, since it's exactly why custom controls exist...

Just add a new UserControl to your project, name it something useful, and add a TextBox and Trackbar to it with the layout you want. Then set up the event handlers as you normally would inside the control, you can even use the Forms Designer for all of this.

Then in your main app, instead of dynamically generating TextBoxes and Trackbars, you add MyCustomControls that encapsulate the functionality you need. If you need to you can then expose a method or property on your custom control like GetValue() that returns the value (as indicated by both the textbox and trackbar).

  • 0

I didn't know about this custom control stuff, this seems to be much easier to work with... but I have a new problem because of it

So I have a control with a bunch of controls, one of them again linking a trackbar to a textBox... when I manipulate the trackBar, it updates the textBox correctly.. I have all the event stuff inside the Control Class... but the problem is, whenever I change the trackBar I want to call my update() method from the main class (Form1)... How would one do this?

Edited by zackiv31
  • 0
  zackiv31 said:
I didn't know about this custom control stuff, this seems to be much easier to work with... but I have a new problem because of it

So I have a control with a bunch of controls, one of them again linking a trackbar to a textBox... when I manipulate the trackBar, it updates the textBox correctly.. I have all the event stuff inside the Control Class... but the problem is, whenever I change the trackBar I want to call my update() method from the main class (Form1)... How would one do this?

Ideally, your control would expose an event that would notify any listeners that the trackbar has changed.

  • 0

You would create a delegate and an event that are public in your user control, and when you handle the trackbar change event in your user control, you fire another event indicating that it changed to the 'outside' world.

using System;
using System.ComponentModel;
using System.Windows.Forms;

namespace cs3
{
	public delegate void ValueChangedHandler(object sender, int newValue);

	public partial class UserControl1 : UserControl
	{
		public UserControl1()
		{
			InitializeComponent();
			textBox1.Text = trackBar1.Value.ToString();
		}

		[Category("Action")]
		public event ValueChangedHandler ValueChanged;

		private void trackBar1_ValueChanged(object sender, EventArgs e)
		{
			textBox1.Text = trackBar1.Value.ToString();
			OnValueChanged(trackBar1.Value);
		}

		protected void OnValueChanged(int newValue)
		{
			if (ValueChanged != null)
				ValueChanged(this, newValue);
		}
	}
}

  • 0
  zackiv31 said:
		[Category("Action")]
		  public event ValueChangedHandler ValueChanged;

This is new to me.. but seems interesting... what exactly are the [] for? What does it represent or tell he compiler?

It's an attribute for the designer. Add the control to your form, and then select the control. In the Properties pane of the designer, you see properties categorized. If you click on the Events button(the lightning bolt), it lists the events that your control exposes. If you didn't put the CategoryAttribute above your event, it would show up at the bottom of the list in the Misc category.

Attributes are one of the cool aspects of .NET that can be leveraged in many interesting ways. You could effectively describe your class with attributes and discover the metadata at runtime, and perform actions based on it. I've built a framework that utilized attributes to describe how properties should be validated. It was only a proof of concept, but it worked quite well. I'm now seeing that same idea show up in other frameworks, such as the Castle Project's MVC framework.

Edited by azcodemonkey
  • 0

here's my userControl:

	public delegate void ValueChangedHandler(object sender);

	public partial class ListBag : UserControl
	{
		[Category("Action")]
		public event ValueChangedHandler ValueChanged;

here's the declaration in Form1:

ListBag lb = new ListBag();
					lb.ValueChanged += new ValueChangedHandler;

It doesn't recognize this, it tries to make it " += ValueChangedHandler(someNameHere)"...

  • 0

But you said you wanted your Form1 to know when something changed inside the user control. That's why you need to have a method inside Form1 that gets called when the event is fired. It can be named anything you want (like OnListBagValueChanged or something).

  • 0
  zackiv31 said:
wo wo wo... OnValueChanged is a part of my custom UserControl... therefore Form1 has no idea abou the inner workings of it...

someone confirm this? (and help still)

Your form needs to have a method that matches the signature of the delegate of your control.

protected void UserCtrlValueChanged(object sender)
{
	...
}

Then you can use the += syntax to add a new handler in your form's InitializeComponent method.

userCtrlInstance.ValueChanged += new ValueChangedHandler(UserCtrlValueChanged);

You should be able to do this completely through the designer. Add the control to your form, select the control, go to the Properties panel in the IDE and select the Event(lightning bolt), and double-click the ValueChanged event in the UI. This will do all of the above correctly for you.

Edit: Brandon got it. :)

  • 0

Not that it matters much, but if that's what you delegate looks like - you don't actually need a custom one. Just use the built-in EventHandler delegate. Other than that little nit, it looks like you've got things figured out.

  • 0

Well it depends. Are you using:

public delegate void ValueChangedHandler(object sender);

or

public delegate void ValueChangedHandler(object sender, int newValue);

If the latter, then just keep it as is. If the former, then you don't need to declare that delegate at all.

protected void UserCtrlValueChanged(object sender)
{
...
}

in your main form, becomes

protected void UserCtrlValueChanged(object sender, EventArgs e)
{
...
}

And everywhere you used "ValueChangedHandler" before, you could now use just the built-in EventHandler delegate.

For example:

userCtrlInstance.ValueChanged += new ValueChangedHandler(UserCtrlValueChanged);

becomes

userCtrlInstance.ValueChanged += new EventHandler(UserCtrlValueChanged);

But if you are using a custom delegate to pass an integer with the new value, then you'll want to keep doing it the way you are. And when the event is raised, you just pass EventArgs.Empty for the second parameter.

This topic is now closed to further replies.
  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Posts

    • how big is your HDD that only has 100gb left? I take it this the main drive.  Is this a pc or laptop? I ask because changing hdd in pcs are much easier. You sure a good clean/purge of data wouldn't clear up space - have you ran disk cleanup? Which is part of windows..  You can for sure move data to your external drive, install programs to it, etc - but using it to store updates?   
    • How to record screen as GIF in Windows 11 by Taras Buria The Snipping Tool app is already quite a capable program for screenshots and screen recordings. Still, there is always room for improvement, and many users agree that the app needs the ability to save screen recordings as GIFs. Microsoft heard those users, and recent updates introduced the long-requested feature, allowing you to record your screen as a GIF. Here is how to do it. Record screen as a GIF in Windows 11 Note: By the time of publishing this article, GIF support in Snipping Tool is only available to Windows Insiders. However, you can enable that feature on stable Windows 11 releases as well; here is how: Go to store.rg-adguard.net, select ProductID in the first drop-down, paste 9MZ95KL8MR0L into the search box, and select Fast in the last drop-down. Press the checkmark button. Find and download Microsoft.ScreenSketch_2022.2505.21.0_neutral_~_8wekyb3d8bbwe.msixbundle in the list of apps. The version number could be newer, just make sure you are downloading an msixbundle file. Note that the browser will warn you about downloading a potentially harmful file. Open the file and click Update. Download ViveTool from GitHub and unpack the files in a convenient and easy-to-find folder. Run Command Prompt as Administrator and navigate to the folder containing the ViveTool files with the CD command. For example, if you have placed ViveTool in C:\Vive, type CD C:\Vive. Type vivetool /enable /id:47081492 and press Enter. The steps above might seem a bit tedious, but that is the only way to get GIF support in Snipping Tool without enrolling your device in the Windows Insider program. We will update the article once the feature is publicly available, so there is no need to jump through all the hoops just to make it work. Tip: You can always roll back Snippint Tool to the latest version from the Microsoft Store by uninstalling it and downloading it again. Now, with GIF support enabled in Snipping Tool, here is how to save a screen recording as a GIF in Windows 11: Press Win + Shift + S, select screen recording mode and record whatever you want. After the recording is over, Snipping Tool will open your video so that you can view, trim, or save it. At this point, all you have to do is click the GIF button in the upper-right corner. On the next screen, select your GIF quality and click Export to save as a file or Copy to copy it to the clipboard. And that is how you save screen recordings as GIFs in Windows 11. Note that Snipping Tool can only save GIFs for up to 30 seconds. Anything beyond that will be cut off. You might think that Clipchamp, Windows 11's built-in video editor, is a good option when you want to save a screen recording as a GIF. However, it really sucks at that. The video duration is capped at just 15 seconds, which is even worse than the Snipping Tool, and the output resolution is hilariously low. The latter makes it impossible to distinguish any details, and all you get is a blurry, pixelated mess. No, Clipchamp is not a good option for that. If you want to create GIFs that are longer than 30 seconds, a good option is to go with apps like ShareX, which is extremely flexible and customizable (and also free, which makes it one of our favorite must-have apps for Windows 11). Alternatively, you can record a video using the Snipping Tool and then convert it to a GIF using web-based services like Ezgif, another great free utility. Keep in mind that the larger your video resolution and the longer its duration, the bigger the final GIF size. Depending on the settings, GIFs could reach hundreds of megabytes, so you have to set your expectations correctly (and so do the settings, too).
    • I'll give you an example of "the settings problem." As awful as the HP Smart app is, it's magnitudes more useful than Settings when I need to do some deep dive stuff on my HP Officejet.
    • I hate to defend Apple but this marketing and they are only "desperate" to move from #3 to #1 for biggest company in the world.
    • There's very granular stuff in the legacy Control Panel that will probably never be accessible from settings. But that stuff will still be there if you know where to look.
  • Recent Achievements

    • Week One Done
      habso earned a badge
      Week One Done
    • Week One Done
      DXB APPS earned a badge
      Week One Done
    • One Month Later
      DecaffKnight94 earned a badge
      One Month Later
    • Dedicated
      S.P earned a badge
      Dedicated
    • One Month Later
      adxnksd42031 earned a badge
      One Month Later
  • Popular Contributors

    1. 1
      +primortal
      661
    2. 2
      ATLien_0
      252
    3. 3
      Michael Scrip
      234
    4. 4
      Steven P.
      151
    5. 5
      +FloatingFatMan
      148
  • Tell a friend

    Love Neowin? Tell a friend!