C# - Passing custom arguments to events

Question

So I was trying to send custom arguments to an event, but it never worked, I tried so many different methods, but I never got it to work, So basically!

public void CreateEmojiList()
        {
            CreateAllEmojis();
            int btnCount = 0;

            foreach(Emoji emoji in emojiList)
            {
                Button btnEmoji = new Button();
                btnEmoji.Size = new Size(40, 36);
                btnEmoji.FlatStyle = FlatStyle.Flat;
                btnEmoji.FlatAppearance.MouseDownBackColor = Color.Cyan;
                btnEmoji.Cursor = Cursors.Hand;
                btnEmoji.Font = new Font("Bahnschrift", 6.75f);
                btnEmoji.Text = emoji.EmojiText;
                btnEmoji.Top = (panel_main.Controls.OfType<Button>().Count<Button>() / 4) * (1 + btnEmoji.Height) + 6;
                btnEmoji.Left = (btnEmoji.Width + 1) * btnCount + 6;
                panel_main.Controls.Add(btnEmoji);
                btnEmoji.Click += //What do I do here?
;                btnCount++;

                if (btnCount == 4)
                    btnCount = 0;
            }
        }

        protected virtual void OnEmojiClick(EmojiClickEventArgs e)
        {
            if (this.EmojiClick != null)
                EmojiClick(e);
        }

this is the class I want to use to pass my arguments:

public class EmojiClickEventArgs : EventArgs
    {
        private string emojiText;
        private string emojiName;

        public EmojiClickEventArgs(string EmojiText, string EmojiName)
        {
            this.EmojiText = EmojiText;
            this.EmojiName = EmojiName;
        }

        public string EmojiText { get { return emojiText; } set { emojiText = value; } }
        public string EmojiName { get { return emojiName; } set { emojiName = value; } }
    }

I want to get those two values from emoji.EmojiText and emoji.EmojiName

What arguments are you looking to pass? Looks like you are using a standard button, so you won't be able to change how it works. — LarsTech, Dec 29 '17 at 23:28
What is the difference between an "EmojiClickEvent" and a normal button Click event? You are using a button, the eventhandler is defined by the button class. You could pass a derived class of [RoutedEventArgs](https://msdn.microsoft.com/de-de/library/system.windows.routedeventargs(v=vs.110).aspx) - but what for?? — Patrick Artner, Dec 29 '17 at 23:34
The event signature is defined in the class, so unless you own the class code, you can't change the signature. But you can still do whatever you want inside the event. What specifically are you expecting to do with the event args? — Rufus L, Dec 29 '17 at 23:34
Possibly you should read about how events work and how to create them in your own classes in order to gain a deeper understanding: https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/events/ — Rufus L, Dec 29 '17 at 23:36
thread updated, I realized that I didn't provide enough information! — Oussama Essamadi, Dec 29 '17 at 23:37
But you are using a `Button` control. It has no concept of that event args class. How would those values get set by the button? Forget about events for a minute and describe the functionality that you're trying to implement here so that people can help point you to a better way. — Rufus L, Dec 29 '17 at 23:38
I have a class called Emoji that has two properties (EmojiText and EmojiName), I made a list called emojiList that I added multiple Emoji objects to, I'm creating for each emoji in that list a button so that when I press each button, it should return the appropriate EmojiText it's assigned to. — Oussama Essamadi, Dec 29 '17 at 23:41

score 2 · Answer 1 · answered Dec 30 '17 at 01:40

You can take advantage of closures to "package up" the additional event data for each button's event handler. Just make sure not to close over the loop variable.

    public void CreateEmojiList()
    {
        CreateAllEmojis();
        int btnCount = 0;

        foreach(Emoji emoji in emojiList)
        {
            Button btnEmoji = new Button();
            btnEmoji.Size = new Size(40, 36);
            btnEmoji.FlatStyle = FlatStyle.Flat;
            btnEmoji.FlatAppearance.MouseDownBackColor = Color.Cyan;
            btnEmoji.Cursor = Cursors.Hand;
            btnEmoji.Font = new Font("Bahnschrift", 6.75f);
            btnEmoji.Text = emoji.EmojiText;
            btnEmoji.Top = (panel_main.Controls.OfType<Button>().Count<Button>() / 4) * (1 + btnEmoji.Height) + 6;
            btnEmoji.Left = (btnEmoji.Width + 1) * btnCount + 6;
            panel_main.Controls.Add(btnEmoji);
            var emojiCopy = emoji; //don't close on the loop variable!
            btnEmoji.Click += (sender,args) => OnEmojiClick(emojiCopy);
            btnCount++;

            if (btnCount == 4)
                btnCount = 0;
        }
    }

    protected virtual void OnEmojiClick(Emoji emoji)
    {
        //do something
    }

Sweeper · Accepted Answer · 2017-12-30T00:19:01.787

1

One way is to inherit from Button and create a class called EmojiButton. You then declare a delegate that matches the signature of the your event handler. After that, declare an event using the delegate in the EmojiButton class, add property like EmojiText and EmojiName to the button subclass as well. Finally you need to link the button click event with your custom event. Whenever the button is clicked, raise your event and pass your arguments i.e. this.EmojiText, this.EmojiName.

Another way is to assign your Emoji objects to the Tag property. You can then write the event handler with the normal EventHandler signature (object sender, EventArgs e), and look at what the sender's Tag is. You then cast the Tag to an Emoji and access its properties.

edited Dec 30 '17 at 00:19

answered Dec 30 '17 at 00:14

Sweeper

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`somehow encode EmojiText and EmojiName into the button's Name property.` If you are going to go that route, might as well just use the Tag property. Assuming this is WinForms. – LarsTech Dec 30 '17 at 00:17
@LarsTech Oh yeah! I forgot about that! – Sweeper Dec 30 '17 at 00:19
How exactly can I access its tag? I tried sender.Tag but obviously it didn't work. – Oussama Essamadi Dec 30 '17 at 00:34
@OussamaEssamadi You need to cast `sender` first: `((Button)sender).Tag` – Sweeper Dec 30 '17 at 00:35

Tommaso Belluzzo · Answer 3 · 2017-12-30T01:03:44.903

The fastest solution that comes to my mind and that doesn't imply the definition of custom UserControl classes, the subclassing of Button and other similar practices is:

btnEmoji.Click += (sender, e) =>
{
    Button b = (Button)sender;

    // let's suppose that the button name corresponds to the emoji name
    String emojiName = b.Name; 
    // let's suppose that the button tag contains the emoji text
    String emojiText = (String)b.Tag;

    Emoji_Clicked(sender, e, (new EmojiClickEventArgs(emojiText, emojiName)));
};

private void Emoji_Clicked(Object sender, EventArgs e, EmojiClickEventArgs ee)
{
    // Your code...
}

score 0 · Answer 4 · answered Dec 30 '17 at 13:29

First and foremost thing you need to define delegate ,then create an instance.

class Emojis
{
       // public delegate void EmojiClickEventHandler(object sender,EventArgs args);
       //public event EmojiEventHandler EmojiClicked;
       //you can use above two lines or replace them instead below code.
        public event EventHandler<EmojiClickEventArgs> EmojiClicked;
        public void CreateEmojiList()
         {
             CreateAllEmojis();
             int btnCount = 0;
             //rest of the code
            panel_main.Controls.Add(btnEmoji);
            btnEmoji.Click += OnEmojiClick(btnEmoji);
            btnCount++;
        }

   protected virtual void OnEmojiClick(Button emoji)
   {
    //Here null check to handle if no subscribers for the event
    if(EmojiClicked!=null)
       {
           //there is no name property define for emoji but only text hence passing only text.
          EmojiClicked(this ,new  EmojiClickEventArgs(emoji.Text,emoji.Text){ });
       }
   }
   private void Emoji_Clicked(Object sender, EmojiClickEventArgs args)
        {
            Button mybutton = sender as Button;
            Console.WriteLine("emoji text "+ args.Text);
        }

}

C# - Passing custom arguments to events

4 Answers4