Solución:
Algo que me ha funcionado:
this.waterMarkActive = true;
this.textBox.ForeColor = Color.Gray;
this.textBox.Text = "Type here";
this.textBox.GotFocus += (source, e) =>
{
if (this.waterMarkActive)
{
this.waterMarkActive = false;
this.textBox.Text = "";
this.textBox.ForeColor = Color.Black;
}
};
this.textBox.LostFocus += (source, e) =>
{
if (!this.waterMarkActive && string.IsNullOrEmpty(this.textBox.Text))
{
this.waterMarkActive = true;
this.textBox.Text = "Type here";
this.textBox.ForeColor = Color.Gray;
}
};
Dónde bool waterMarkActive es una variable miembro de clase y textBox es el TextBox. Sin embargo, esto probablemente debería encapsularse 🙂 Puede haber algunos problemas con este enfoque, pero actualmente no tengo conocimiento de ninguno.
Recientemente descubrí que Windows admite marcas de agua en cuadros de texto; se llaman carteles de señal (ver aquí). Es muy fácil de implementar:
// Within your class or scoped in a more appropriate location:
[DllImport("user32.dll")]
private static extern IntPtr SendMessage(IntPtr hWnd, int Msg, int wParam, [MarshalAs(UnmanagedType.LPWStr)] string lParam);
// In your constructor or somewhere more suitable:
SendMessage(textBox.Handle, 0x1501, 1, "Please type here.");
Dónde textBox es una instancia de TextBox, 0x1501 es el código del mensaje de Windows EM_SETCUEBANNER, los wParam puede ser TRUE (distinto de cero) o FALSE (cero) y lParam es la marca de agua que le gustaría mostrar. wParam indica cuándo se debe mostrar el banner de la señal; si se establece en TRUE entonces, el banner de cue se mostrará incluso cuando el control esté enfocado.
Lo que busca es un TextBox con un “filigrana“.
Aquí hay una implementación de muestra para C #, todos los créditos para Wael Alghool.
La parte relevante de su código es:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Drawing;
namespace wmgCMS
{
class WaterMarkTextBox : TextBox
{
private Font oldFont = null;
private Boolean waterMarkTextEnabled = false;
#region Attributes
private Color _waterMarkColor = Color.Gray;
public Color WaterMarkColor
{
get { return _waterMarkColor; }
set { _waterMarkColor = value; Invalidate();/*thanks to Bernhard Elbl
for Invalidate()*/ }
}
private string _waterMarkText = "Water Mark";
public string WaterMarkText
{
get { return _waterMarkText; }
set { _waterMarkText = value; Invalidate(); }
}
#endregion
//Default constructor
public WaterMarkTextBox()
{
JoinEvents(true);
}
//Override OnCreateControl ... thanks to "lpgray .. codeproject guy"
protected override void OnCreateControl()
{
base.OnCreateControl();
WaterMark_Toggel(null, null);
}
//Override OnPaint
protected override void OnPaint(PaintEventArgs args)
{
// Use the same font that was defined in base class
System.Drawing.Font drawFont = new System.Drawing.Font(Font.FontFamily,
Font.Size, Font.Style, Font.Unit);
//Create new brush with gray color or
SolidBrush drawBrush = new SolidBrush(WaterMarkColor);//use Water mark color
//Draw Text or WaterMark
args.Graphics.DrawString((waterMarkTextEnabled ? WaterMarkText : Text),
drawFont, drawBrush, new PointF(0.0F, 0.0F));
base.OnPaint(args);
}
private void JoinEvents(Boolean join)
{
if (join)
{
this.TextChanged += new System.EventHandler(this.WaterMark_Toggel);
this.LostFocus += new System.EventHandler(this.WaterMark_Toggel);
this.FontChanged += new System.EventHandler(this.WaterMark_FontChanged);
//No one of the above events will start immeddiatlly
//TextBox control still in constructing, so,
//Font object (for example) couldn't be catched from within
//WaterMark_Toggle
//So, call WaterMark_Toggel through OnCreateControl after TextBox
//is totally created
//No doupt, it will be only one time call
//Old solution uses Timer.Tick event to check Create property
}
}
private void WaterMark_Toggel(object sender, EventArgs args )
{
if (this.Text.Length <= 0)
EnableWaterMark();
else
DisbaleWaterMark();
}
private void EnableWaterMark()
{
//Save current font until returning the UserPaint style to false (NOTE:
//It is a try and error advice)
oldFont = new System.Drawing.Font(Font.FontFamily, Font.Size, Font.Style,
Font.Unit);
//Enable OnPaint event handler
this.SetStyle(ControlStyles.UserPaint, true);
this.waterMarkTextEnabled = true;
//Triger OnPaint immediatly
Refresh();
}
private void DisbaleWaterMark()
{
//Disbale OnPaint event handler
this.waterMarkTextEnabled = false;
this.SetStyle(ControlStyles.UserPaint, false);
//Return back oldFont if existed
if(oldFont != null)
this.Font = new System.Drawing.Font(oldFont.FontFamily, oldFont.Size,
oldFont.Style, oldFont.Unit);
}
private void WaterMark_FontChanged(object sender, EventArgs args)
{
if (waterMarkTextEnabled)
{
oldFont = new System.Drawing.Font(Font.FontFamily,Font.Size,Font.Style,
Font.Unit);
Refresh();
}
}
}
}
Basado en la respuesta de @ Pooven (¡gracias!), Creé esta clase. Funciona para mi.
/// <summary>
/// A textbox that supports a watermak hint.
/// </summary>
public class WatermarkTextBox : TextBox
{
/// <summary>
/// The text that will be presented as the watermak hint
/// </summary>
private string _watermarkText = "Type here";
/// <summary>
/// Gets or Sets the text that will be presented as the watermak hint
/// </summary>
public string WatermarkText
{
get { return _watermarkText; }
set { _watermarkText = value; }
}
/// <summary>
/// Whether watermark effect is enabled or not
/// </summary>
private bool _watermarkActive = true;
/// <summary>
/// Gets or Sets whether watermark effect is enabled or not
/// </summary>
public bool WatermarkActive
{
get { return _watermarkActive; }
set { _watermarkActive = value; }
}
/// <summary>
/// Create a new TextBox that supports watermak hint
/// </summary>
public WatermarkTextBox()
{
this._watermarkActive = true;
this.Text = _watermarkText;
this.ForeColor = Color.Gray;
GotFocus += (source, e) =>
{
RemoveWatermak();
};
LostFocus += (source, e) =>
{
ApplyWatermark();
};
}
/// <summary>
/// Remove watermark from the textbox
/// </summary>
public void RemoveWatermak()
{
if (this._watermarkActive)
{
this._watermarkActive = false;
this.Text = "";
this.ForeColor = Color.Black;
}
}
/// <summary>
/// Applywatermak immediately
/// </summary>
public void ApplyWatermark()
{
if (!this._watermarkActive && string.IsNullOrEmpty(this.Text)
|| ForeColor == Color.Gray )
{
this._watermarkActive = true;
this.Text = _watermarkText;
this.ForeColor = Color.Gray;
}
}
/// <summary>
/// Apply watermak to the textbox.
/// </summary>
/// <param name="newText">Text to apply</param>
public void ApplyWatermark(string newText)
{
WatermarkText = newText;
ApplyWatermark();
}
}
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