Edit Control With Hint C# - Tạo mặt nạ gợi nhớ cho các controls nhập văn bản C#

Bạn đang muốn tạo một mặt nạ gợi nhớ trên ô nhập tài khoản người dùng hoặc mật khẩu tương tự như các ứng dụng có yêu cầu đăng nhập trên các web-blog có kiểu như dưới đây.

Tạo mặt nạ cho các control nhập liệu từ người dùng

Mã nguồn chương trình: Sử dụng ngôn ngữ lập trình C#

Source: http://www.aaronlerch.com/blog/2007/12/01/watermarked-edit-controls/
Các bạn có thể download trực tiếp các file cài đặt *.cs tại đây:  CueTextBox.cs, CueComboBox.cs, và CueToolStripTextBox.cs

CueTextbox.cs

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Text;

using System.Windows.Forms;

using System.Runtime.InteropServices;

namespace Lerch.Samples

{

    public class CueTextBox : TextBox

    {

        #region PInvoke Helpers

        private static uint ECM_FIRST = 0x1500;

        private static uint EM_SETCUEBANNER = ECM_FIRST + 1;

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]

        private static extern IntPtr SendMessage(HandleRef hWnd, uint Msg, IntPtr wParam, String lParam);

        #endregion PInvoke Helpers

        #region CueText

        private string _cueText = String.Empty;

        ///

        /// Gets or sets the text the will display as a cue to the user.

        ///

        [Description("The text value to be displayed as a cue to the user.")]

        [Category("Appearance")]

        [DefaultValue("")]

        [Localizable(true)]

        public string CueText

        {

            get { return _cueText; }

            set

            {

                if (value == null)

                {

                    value = String.Empty;

                }

                if (!_cueText.Equals(value, StringComparison.CurrentCulture))

                {

                    _cueText = value;

                    UpdateCue();

                    OnCueTextChanged(EventArgs.Empty);

                }

            }

        }

        ///

        /// Occurs when the property value changes.

        ///

        public event EventHandler CueTextChanged;

        [EditorBrowsable(EditorBrowsableState.Advanced)]

        protected virtual void OnCueTextChanged(EventArgs e)

        {

            EventHandler handler = CueTextChanged;

            if (handler != null)

            {

                handler(this, e);

            }

        }

        #endregion CueText

        #region ShowCueTextOnFocus

        private bool _showCueTextWithFocus = false;

        ///

        /// Gets or sets a value indicating whether the will display the

        /// even when the control has focus.

        ///

        [Description("Indicates whether the CueText will be displayed even when the control has focus.")]

        [Category("Appearance")]

        [DefaultValue(false)]

        [Localizable(true)]

        public bool ShowCueTextWithFocus

        {

            get { return _showCueTextWithFocus; }

            set

            {

                if (_showCueTextWithFocus != value)

                {

                    _showCueTextWithFocus = value;

                    UpdateCue();

                    OnShowCueTextWithFocusChanged(EventArgs.Empty);

                }

            }

        }

        ///

        /// Occurs when the property value changes.

        ///

        public event EventHandler ShowCueTextWithFocusChanged;

        [EditorBrowsable(EditorBrowsableState.Advanced)]

        protected virtual void OnShowCueTextWithFocusChanged(EventArgs e)

        {

            EventHandler handler = ShowCueTextWithFocusChanged;

            if (handler != null)

            {

                handler(this, e);

            }

        }

        #endregion ShowCueTextOnFocus

        #region Overrides

        protected override void OnHandleCreated(EventArgs e)

        {

            UpdateCue();

            base.OnHandleCreated(e);

        }

        #endregion Overrides

        private void UpdateCue()

        {

            // If the handle isn't yet created,

            // this will be called when it is created

            if (this.IsHandleCreated)

            {

                SendMessage(new HandleRef(this, this.Handle), EM_SETCUEBANNER, (_showCueTextWithFocus) ? new IntPtr(1) : IntPtr.Zero, _cueText);

            }

        }

    }

}

CueComboBox.cs

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Text;

using System.Windows.Forms;

using System.Runtime.InteropServices;

namespace Lerch.Samples

{

    public class CueComboBox : ComboBox

    {

        #region PInvoke Helpers

        private static uint CB_SETCUEBANNER = 0x1703;

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]

        private static extern IntPtr SendMessage(HandleRef hWnd, uint Msg, IntPtr wParam, String lParam);

        #endregion PInvoke Helpers

        #region CueText

        private string _cueText = String.Empty;

        ///

        /// Gets or sets the text the will display as a cue to the user.

        ///

        [Description("The text value to be displayed as a cue to the user.")]

        [Category("Appearance")]

        [DefaultValue("")]

        [Localizable(true)]

        public string CueText

        {

            get { return _cueText; }

            set

            {

                if (value == null)

                {

                    value = String.Empty;

                }

                if (!_cueText.Equals(value, StringComparison.CurrentCulture))

                {

                    _cueText = value;

                    UpdateCue();

                    OnCueTextChanged(EventArgs.Empty);

                }

            }

        }

        ///

        /// Occurs when the property value changes.

        ///

        public event EventHandler CueTextChanged;

        [EditorBrowsable(EditorBrowsableState.Advanced)]

        protected virtual void OnCueTextChanged(EventArgs e)

        {

            EventHandler handler = CueTextChanged;

            if (handler != null)

            {

                handler(this, e);

            }

        }

        #endregion CueText

        #region Overrides

        protected override void OnHandleCreated(EventArgs e)

        {

            UpdateCue();

            base.OnHandleCreated(e);

        }

        #endregion Overrides

        private void UpdateCue()

        {

            // If the handle isn't yet created,

            // this will be called when it is created

            if (this.IsHandleCreated)

            {

                SendMessage(new HandleRef(this, this.Handle), CB_SETCUEBANNER, IntPtr.Zero, _cueText);

            }

        }

    }

}

CueToolStripTextBox.cs

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Text;

using System.Windows.Forms;

using System.Runtime.InteropServices;

namespace Lerch.Samples

{

    public class CueToolStripTextBox : ToolStripTextBox

    {

        public CueToolStripTextBox()

            : base()

        {

            if (this.Control != null)

            {

                this.Control.HandleCreated += new EventHandler(OnControlHandleCreated);

            }

        }

        public CueToolStripTextBox(string name)

            : base(name)

        {

            if (this.Control != null)

            {

                this.Control.HandleCreated += new EventHandler(OnControlHandleCreated);

            }

        }

        protected override void Dispose(bool disposing)

        {

            if (disposing)

            {

                if (this.Control != null)

                {

                    this.Control.HandleCreated -= new EventHandler(OnControlHandleCreated);

                }

            }

            base.Dispose(disposing);

        }

        void OnControlHandleCreated(object sender, EventArgs e)

        {

            UpdateCue();

        }

        #region PInvoke Helpers

        private static uint ECM_FIRST = 0x1500;

        private static uint EM_SETCUEBANNER = ECM_FIRST + 1;

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]

        private static extern IntPtr SendMessage(HandleRef hWnd, uint Msg, IntPtr wParam, String lParam);

        #endregion PInvoke Helpers

        #region CueText

        private string _cueText = String.Empty;

        ///

        /// Gets or sets the text the will display as a cue to the user.

        ///

        [Description("The text value to be displayed as a cue to the user.")]

        [Category("Appearance")]

        [DefaultValue("")]

        [Localizable(true)]

        public string CueText

        {

            get { return _cueText; }

            set

            {

                if (value == null)

                {

                    value = String.Empty;

                }

                if (!_cueText.Equals(value, StringComparison.CurrentCulture))

                {

                    _cueText = value;

                    UpdateCue();

                    OnCueTextChanged(EventArgs.Empty);

                }

            }

        }

        ///

        /// Occurs when the property value changes.

        ///

        public event EventHandler CueTextChanged;

        [EditorBrowsable(EditorBrowsableState.Advanced)]

        protected virtual void OnCueTextChanged(EventArgs e)

        {

            EventHandler handler = CueTextChanged;

            if (handler != null)

            {

                handler(this, e);

            }

        }

        #endregion CueText

        #region ShowCueTextOnFocus

        private bool _showCueTextWithFocus = false;

        ///

        /// Gets or sets a value indicating whether the will display the

        /// even when the control has focus.

        ///

        [Description("Indicates whether the CueText will be displayed even when the control has focus.")]

        [Category("Appearance")]

        [DefaultValue(false)]

        [Localizable(true)]

        public bool ShowCueTextWithFocus

        {

            get { return _showCueTextWithFocus; }

            set

            {

                if (_showCueTextWithFocus != value)

                {

                    _showCueTextWithFocus = value;

                    UpdateCue();

                    OnShowCueTextWithFocusChanged(EventArgs.Empty);

                }

            }

        }

        ///

        /// Occurs when the property value changes.

        ///

        public event EventHandler ShowCueTextWithFocusChanged;

        [EditorBrowsable(EditorBrowsableState.Advanced)]

        protected virtual void OnShowCueTextWithFocusChanged(EventArgs e)

        {

            EventHandler handler = ShowCueTextWithFocusChanged;

            if (handler != null)

            {

                handler(this, e);

            }

        }

        #endregion ShowCueTextOnFocus

        private void UpdateCue()

        {

            // If the handle isn't yet created,

            // this will be called when it is created

            if ((this.Control != null) && (this.Control.IsHandleCreated))

            {

                SendMessage(new HandleRef(this.Control, this.Control.Handle), EM_SETCUEBANNER, (_showCueTextWithFocus) ? new IntPtr(1) : IntPtr.Zero, _cueText);

            }

        }

    }

}