"include" a class in a windows form C#

Question

I have a Form that contains a few textboxes. when loading the form, I want those textboxes to show a default grayed out text that disappears when the user clicks the textbox. I have used this code:

    private void Form1_Load(object sender, EventArgs e)
    {
        //textbox1 default text
        this.tBox1.Enter += new EventHandler(tBox1_Enter);
        this.textbox1.Leave += new EventHandler(tBox1_Leave);
        tBox1_SetText();
        
        /*...
         same for other textboxes
        */

    }

    /*textbox1 default text*/

    // default greyed out text in tBox1
    public void tBox1_SetText()
    {
        tBox1.Text = "some default text";
        tBox1.ForeColor = Color.Gray;
    }

    // remove default text from tBox1 once cruser is set in
    public void tBox1_Enter(object sender, EventArgs e)
    {
        if (tBox1.ForeColor == Color.Black)
            return;
        tBox1.Text = "";
        tBox1.ForeColor = Color.Black;
    }

    // sets the default text back to tBox1 once cruser is gone
    public void tBox1_Leave(object sender, EventArgs e)
    {
        if (tBox1.Text.Trim() == "")
            tBox1_SetText();
    }

    /*...
     same for other textboxes
    */

since I have a lot of textboxes I would like to move all this code from my form to a separate class (something like DefaultText.cs), create a method in that class ("ShowDefaultText()") and just call this method in form_load so my code would be more understandable. I tried creating this class but there is no #include in C# and I cant use static class/methods because of the instances. how can I do this otherwise?

Answer 1

As Jamiec points out, if you're using .net Core 3.1 or later then there is a TextBox.PlaceholderText property you can use to achieve you aim.

However if you're using .net framework 4.8 (or earlier) which doesn't have that property, the best way to do this is to write a customized TextBox class that does this for you - then you just need to use that instead of TextBox.

For example:

Firstly, add a custom control to your project using Add | New Item and then select "Windows Forms" and choose "Custom Control" and click "Add". Name it something like TextBoxGreyed.

Then edit the implementation to be something like this:

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

namespace WinFormsApp1
{
    public partial class TextBoxGreyed : TextBox
    {
        public TextBoxGreyed()
        {
            InitializeComponent();
            setText();
        }

        [
            Browsable(true),
            Category("Appearance"),
            DefaultValue(""),
            Localizable(true),
            Description("Default text to display when text box is empty")
        ]

        public string DefaultText
        {
            get => _defaultText;

            set
            {
                _defaultText = value;
                setText();
                Invalidate();
            }
        }

        protected override void OnEnter(EventArgs e)
        {
            base.OnEnter(e);

            if (this.ForeColor == Color.Black)
                return;

            this.Text      = "";
            this.ForeColor = Color.Black;
        }

        protected override void OnLeave(EventArgs e)
        {
            base.OnLeave(e);

            if (this.Text.Trim() == "")
                setText();
        }

        void setText()
        {
            this.Text      = _defaultText;
            this.ForeColor = Color.Gray;
        }

        string _defaultText = "";
    }
}

After building, you should see the new custom control at the top of the toolbox in the Forms designer. If you add a TextBoxGreyed to the form and inspect its properties, you should see a DefaultText property that you can set to your desired text.

This is a fairly basic example, but hopefully it will get you started.