Question

有人能指出我对基本Windows窗体TextBox的良好实现，它最初会显示水印文本，当光标进入时会消失吗？我想我可以通过创造性地使用Enter和Leave事件来创建我自己的东西，但我确信在某个地方有一个完全可用的实现。我看到了WPF实现，如果有必要，我可以嵌套它，但原生的WinForms TextBox派生会更好。

到目前为止，我有这个;尚未尝试过，但有没有人看到任何明显的问题？

public class WatermarkTextBox:TextBox
{
    public string WatermarkText { get; set; }

    public Color WatermarkColor { get; set; }

    private Color TextColor { get; set; }

    private bool isInTransition;

    public WatermarkTextBox()
    {
        WatermarkColor = SystemColors.GrayText;
    }

    private bool HasText { get { return Text.IsNotNullOrBlankOr(WatermarkText); }}

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

        if (HasText) return;

        isInTransition = true;
        ForeColor = TextColor;
        Text = String.Empty;
        isInTransition = false;
    }

    protected override void OnForeColorChanged(EventArgs e)
    {
        base.OnForeColorChanged(e);
        if (!isInTransition) //the change came from outside
            TextColor = ForeColor;
    }

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

        if (HasText) return;

        isInTransition = true;
        ForeColor = WatermarkColor;
        Text = WatermarkText.EmptyIfNull();
        isInTransition = false;
    }
}

编辑：上面的内容最终会起到一些作用，但CueProvider工作得更好。这是我的最终实施：

public class WatermarkTextBox:TextBox
{
    private string watermarkText;
    public string WatermarkText
    {
        get { return watermarkText; }
        set
        {
            watermarkText = value;
            if (watermarkText.IsNullOrBlank())
                CueProvider.ClearCue(this);
            else
                CueProvider.SetCue(this, watermarkText);
        }
    }
}

我可以完全集成CueProvider功能，但这种方法很有效。

Answer 1

官方用语是“cue banner”。这是另一种方法，只需继承TextBox即可完成工作。在项目中添加一个新类并粘贴下面显示的代码。编译。从工具箱顶部删除新控件并设置Cue属性。

您可以在设计器中预览Cue值，并将其本地化为表单的Language属性。非常小的降压，很好地证明了Winforms的好部分。

using System;
using System.ComponentModel;
using System.Windows.Forms;
using System.Runtime.InteropServices;

class CueTextBox : TextBox {
    [Localizable(true)]
    public string Cue {
        get { return mCue; }
        set { mCue = value; updateCue(); }
    }

    private void updateCue() {
        if (this.IsHandleCreated && mCue != null) {
            SendMessage(this.Handle, 0x1501, (IntPtr)1, mCue);
        }
    }
    protected override void OnHandleCreated(EventArgs e) {
        base.OnHandleCreated(e);
        updateCue();
    }
    private string mCue;

    // PInvoke
    [DllImport("user32.dll", CharSet = CharSet.Unicode)]
    private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wp, string lp);
}

Answer 2

我已经更新了@Hans Passant上面给出的答案来引入常量，使其与pinvoke.net定义保持一致，并让代码通过FxCop验证。

class CueTextBox : TextBox
{
    private static class NativeMethods
    {
        private const uint ECM_FIRST = 0x1500;
        internal const uint EM_SETCUEBANNER = ECM_FIRST + 1;

        [DllImport("user32.dll", CharSet = CharSet.Unicode)]
        public static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, string lParam);
    }

    private string _cue;

    public string Cue
    {
        get
        {
            return _cue;
        }
        set
        {
            _cue = value;
            UpdateCue();
        }
    }

    private void UpdateCue()
    {
        if (IsHandleCreated && _cue != null)
        {
            NativeMethods.SendMessage(Handle, NativeMethods.EM_SETCUEBANNER, (IntPtr)1, _cue);
        }
    }

    protected override void OnHandleCreated(EventArgs e)
    {
        base.OnHandleCreated(e);
        UpdateCue();
    }
}

编辑：更新PInvoke调用以设置CharSet属性，以确保安全方面的错误。有关详细信息，请参阅SendMessage上的pinvoke.net页面。

Answer 3

[DllImport("user32.dll", CharSet = CharSet.Unicode)]
private static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, string lParam);

消息常量：

private const uint EM_SETCUEBANNER = 0x1501;
private const uint CB_SETCUEBANNER = 0x1703;    // minimum supported client Windows Vista, minimum supported server Windows Server 2008

而imho实现它的最佳方式是作为一种扩展方法因此，对于TextBox控件，语法为：

MyTextBox.CueBanner(false, "Password");

来自代码：

public static void CueBanner(this TextBox textbox, bool showcuewhenfocus, string cuetext)
{
    uint BOOL = 0;
    if (showcuewhenfocus == true) { BOOL = 1; }

    SendMessage(textbox.Handle, EM_SETCUEBANNER, (IntPtr)BOOL, cuetext); ;
}

Answer 4

您可以通过在不同的控件Paint事件中绘制水印，将水印添加到效果很好的文本框（无论是否有多行）。例如：

    Private Sub Panel1_Paint(sender As Object, e As PaintEventArgs) Handles Panel1.Paint
        If TextBox1.Text = "" Then
            TextBox1.CreateGraphics.DrawString("Enter Text Here", Me.Font, New SolidBrush(Color.LightGray), 0, 0)
        End If
    End Sub

-OO-

Answer 5

我为项目编写了可重用的自定义控件类。
也许它可以帮助需要在其项目中实现多个占位符文本框的人。这是C＃和vb.net版本：

C＃：

namespace reusebleplaceholdertextbox
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            // implementation
            CustomPlaceHolderTextbox myCustomTxt = new CustomPlaceHolderTextbox(
                "Please Write Text Here...", Color.Gray, new Font("ARIAL", 11, FontStyle.Italic)
                , Color.Black, new Font("ARIAL", 11, FontStyle.Regular)
                );

            myCustomTxt.Multiline = true;
            myCustomTxt.Size = new Size(200, 50);
            myCustomTxt.Location = new Point(10, 10);
            this.Controls.Add(myCustomTxt);
        }
    }

    class CustomPlaceHolderTextbox : System.Windows.Forms.TextBox
    {
        public string PlaceholderText { get; private set; }
        public Color PlaceholderForeColor { get; private set; }
        public Font PlaceholderFont { get; private set; }

        public Color TextForeColor { get; private set; }
        public Font TextFont { get; private set; }

        public CustomPlaceHolderTextbox(string placeholdertext, Color placeholderforecolor,
            Font placeholderfont, Color textforecolor, Font textfont)
        {
            this.PlaceholderText = placeholdertext;
            this.PlaceholderFont = placeholderfont;
            this.PlaceholderForeColor = placeholderforecolor;
            this.PlaceholderFont = placeholderfont;
            this.TextForeColor = textforecolor;
            this.TextFont = textfont;
            if (!string.IsNullOrEmpty(this.PlaceholderText))
            {
                SetPlaceHolder(true);
                this.Update();
            }
        }

        private void SetPlaceHolder(bool addEvents)
        {
            if (addEvents)
            {  
                this.LostFocus += txt_lostfocus;
                this.Click += txt_click;
            }

            this.Text = PlaceholderText;
            this.ForeColor = PlaceholderForeColor;
            this.Font = PlaceholderFont;
        }

        private void txt_click(object sender, EventArgs e)
        {
            // IsNotFirstClickOnThis:
            // if there is no other control in the form
            // we will have a problem after the first load
            // because we dont other focusable control to move the focus to
            // and we dont want to remove the place holder
            // only on first time the place holder will be removed by click event
            RemovePlaceHolder();
            this.GotFocus += txt_focus;
            // no need for this event listener now
            this.Click -= txt_click;
        }

        private void RemovePlaceHolder()
        {
            this.Text = "";
            this.ForeColor = TextForeColor;
            this.Font = TextFont;
        }
        private void txt_lostfocus(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(this.Text))
            {
                // set placeholder again
                SetPlaceHolder(false);
            }
        }

        private void txt_focus(object sender, EventArgs e)
        {
            if (this.Text == PlaceholderText)
            {
                // IsNotFirstClickOnThis:
                // if there is no other control in the form
                // we will have a problem after the first load
                // because we dont other focusable control to move the focus to
                // and we dont want to remove the place holder
                RemovePlaceHolder();
            }
        }
    }
}

VB.NET：

Namespace CustomControls

    Public Class PlaceHolderTextBox
        Inherits System.Windows.Forms.TextBox

        Public Property PlaceholderText As String
        Public Property PlaceholderForeColor As Color
        Public Property PlaceholderFont As Font
        Public Property TextForeColor As Color
        Public Property TextFont As Font

        Public Sub New(ByVal placeholdertext As String, ByVal placeholderforecolor As Color, ByVal placeholderfont As Font, ByVal txtboxbackcolor As Color, ByVal textforecolor As Color, ByVal textfont As Font)
            Me.PlaceholderText = placeholdertext
            Me.PlaceholderFont = placeholderfont
            Me.PlaceholderForeColor = placeholderforecolor
            Me.PlaceholderFont = placeholderfont
            Me.TextForeColor = textforecolor
            Me.TextFont = textfont
            Me.BackColor = txtboxbackcolor
            If Not String.IsNullOrEmpty(Me.PlaceholderText) Then
                SetPlaceHolder(True)
                Me.Update()
            End If
        End Sub

        Private Sub SetPlaceHolder(ByVal addEvents As Boolean)
            If addEvents Then
                AddHandler Me.LostFocus, AddressOf txt_lostfocus
                AddHandler Me.Click, AddressOf txt_click
            End If

            Me.Text = PlaceholderText
            Me.ForeColor = PlaceholderForeColor
            Me.Font = PlaceholderFont
        End Sub

        Private Sub txt_click(ByVal sender As Object, ByVal e As EventArgs)
            RemovePlaceHolder()
            AddHandler Me.GotFocus, AddressOf txt_focus
            RemoveHandler Me.Click, AddressOf txt_click
        End Sub

        Private Sub RemovePlaceHolder()
            Me.Text = ""
            Me.ForeColor = TextForeColor
            Me.Font = TextFont
        End Sub

        Private Sub txt_lostfocus(ByVal sender As Object, ByVal e As EventArgs)
            If String.IsNullOrEmpty(Me.Text) Then
                SetPlaceHolder(False)
            End If
        End Sub

        Private Sub txt_focus(ByVal sender As Object, ByVal e As EventArgs)
            If Me.Text = PlaceholderText Then
                RemovePlaceHolder()
            End If
        End Sub
    End Class

End Namespace

Answer 6

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

namespace PlaceHolderTextBoxCSharp
{
    public class CTextBox : TextBox
    {
        private Panel contenedor;
        protected string texto = "PlaceHolderText";
        protected Color colorTextoDefault = Color.Gray;
        public Color colorTexto = Color.Gray;
        protected Color colorTextoObligatorio = Color.Red;
        private Font fuente;
        private SolidBrush establecerColorTexto;
        private bool obligatoriedad = false;
        private bool colorConFoco = false;
        private int vuelta = 0;

        public CTextBox()
        {
            Inicializar();
        }

        private void Inicializar()
        {
            fuente = Font;
            CharacterCasing = CharacterCasing.Upper;
            contenedor = null;

            MuestraPlaceHolder();

            Leave += new EventHandler(PierdeFoco);
            TextChanged += new EventHandler(CambiaTexto);
        }

        private void EliminaPlaceHolder()
        {
            if (contenedor != null)
            {
                Controls.Remove(contenedor);
                contenedor = null;
            }
        }

        private void MuestraPlaceHolder()
        {
            if (contenedor == null && TextLength <= 0)
            {
                contenedor = new Panel();
                contenedor.Paint += new PaintEventHandler(contenedorPaint);
                contenedor.Invalidate();
                contenedor.Click += new EventHandler(contenedorClick);
                Controls.Add(contenedor);
            }
        }

        private void contenedorClick(object sender, EventArgs e)
        {
            Focus();
        }

        private void contenedorPaint(object sender, PaintEventArgs e)
        {
            contenedor.Location = new Point(2, 0);
            contenedor.Height = Height;
            contenedor.Width = Width;
            contenedor.Anchor = AnchorStyles.Left | AnchorStyles.Right;
            establecerColorTexto = new SolidBrush(colorTexto);
            Graphics g = e.Graphics;
            g.DrawString(texto, fuente, establecerColorTexto, new PointF(-1f, 1f));
        }

        private void PierdeFoco(object sender, EventArgs e)
        {
            if (TextLength > 0)
            {
                EliminaPlaceHolder();
            }
            else
            {
                if (obligatoriedad == true)
                {
                    colorTexto = colorTextoObligatorio;
                }
                else
                {
                    colorTexto = colorTextoDefault;
                }

                Invalidate();
            }
        }

        private void CambiaTexto(object sender, EventArgs e)
        {
            if (TextLength > 0)
            {
                EliminaPlaceHolder();
            }
            else
            {
                MuestraPlaceHolder();

                vuelta += 1;

                if (vuelta >= 1 && obligatoriedad == true)
                {
                    colorTexto = colorTextoObligatorio;
                }
            }
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);
            MuestraPlaceHolder();
        }

        protected override void OnInvalidated(InvalidateEventArgs e)
        {
            base.OnInvalidated(e);

            if (contenedor != null)
            {
                contenedor.Invalidate();
            }
        }

        [Category("Atributos PlaceHolder")]
        [Description("Establece el texto a mostrar.")]

        public string PlaceHolderText
        {
            get
            {
                return texto;
            }
            set
            {
                texto = value;
                Invalidate();
            }
        }

        [Category("Atributos PlaceHolder")]
        [Description("Establece el estilo de fuente del PlaceHolder.")]

        public Font PlaceHolderFont
        {
            get
            {
                return fuente;
            }
            set
            {
                fuente = value;
                Invalidate();
            }
        }

        [Category("Atributos PlaceHolder")]
        [Description("Indica si el campo es obligatorio.")]

        public bool PlaceHolderFieldRequired
        {
            get
            {
                return obligatoriedad;
            }
            set
            {
                obligatoriedad = value;
                Invalidate();
            }
        }
    }
}

Answer 7

在.NET Core上使用WinForms：

.NET Core中已大大简化了此操作。您可以通过修改TextBox的新PlaceholderText属性直接添加占位符文本。

public virtual string PlaceholderText { get; set; }

请注意，如果要获取彩色的占位符文本，可能仍需要编辑ForeColor。当“文本”字段为null或为空时，将显示“ PlaceholderText”字段。

Answer 8

使用.Net Core 3，在TextBox中引入了一个属性：PlaceHolderText

如果要在FrameWork应用程序中使用此代码，则可以从official open source code提取所需的代码部分，并将其放在TextBox后代中（请参阅license）。

这支持多行TextBox以及RTL文本。

public class PlaceHolderTextBox : TextBox
{
    private const int WM_KILLFOCUS = 0x0008;
    private const int WM_PAINT = 0x000F;

    private string _placeholderText;

    protected override void WndProc(ref Message m)
    {
        base.WndProc(ref m);

        if (this.ShouldRenderPlaceHolderText(m))
        {
            using Graphics g = this.CreateGraphics();
            this.DrawPlaceholderText(g);
        }
    }

    #region PlaceHolder

    /// <summary>
    ///  Gets or sets the text that is displayed when the control has no text and does not have the focus.
    /// </summary>
    /// <value>The text that is displayed when the control has no text and does not have the focus.</value>
    [Localizable(true), DefaultValue("")]
    public virtual string PlaceholderText
    {
        get => _placeholderText;
        set
        {
            if (value == null)
            {
                value = string.Empty;
            }

            if (_placeholderText != value)
            {
                _placeholderText = value;
                if (this.IsHandleCreated)
                {
                    this.Invalidate();
                }
            }
        }
    }

    //-------------------------------------------------------------------------------------------------

    /// <summary>
    ///  Draws the <see cref="PlaceholderText"/> in the client area of the <see cref="TextBox"/> using the default font and color.
    /// </summary>
    private void DrawPlaceholderText(Graphics graphics)
    {
        TextFormatFlags flags = TextFormatFlags.NoPadding | TextFormatFlags.Top |
                                TextFormatFlags.EndEllipsis;
        Rectangle rectangle = this.ClientRectangle;

        if (this.RightToLeft == RightToLeft.Yes)
        {
            flags |= TextFormatFlags.RightToLeft;
            switch (this.TextAlign)
            {
                case HorizontalAlignment.Center:
                    flags |= TextFormatFlags.HorizontalCenter;
                    rectangle.Offset(0, 1);
                    break;
                case HorizontalAlignment.Left:
                    flags |= TextFormatFlags.Right;
                    rectangle.Offset(1, 1);
                    break;
                case HorizontalAlignment.Right:
                    flags |= TextFormatFlags.Left;
                    rectangle.Offset(0, 1);
                    break;
            }
        }
        else
        {
            flags &= ~TextFormatFlags.RightToLeft;
            switch (this.TextAlign)
            {
                case HorizontalAlignment.Center:
                    flags |= TextFormatFlags.HorizontalCenter;
                    rectangle.Offset(0, 1);
                    break;
                case HorizontalAlignment.Left:
                    flags |= TextFormatFlags.Left;
                    rectangle.Offset(1, 1);
                    break;
                case HorizontalAlignment.Right:
                    flags |= TextFormatFlags.Right;
                    rectangle.Offset(0, 1);
                    break;
            }
        }

        TextRenderer.DrawText(graphics, this.PlaceholderText, this.Font, rectangle, SystemColors.GrayText, this.BackColor, flags);
    }
    
    private bool ShouldRenderPlaceHolderText(in Message m) =>
        !string.IsNullOrEmpty(this.PlaceholderText) &&
        (m.Msg == WM_PAINT || m.Msg == WM_KILLFOCUS) &&
        !this.GetStyle(ControlStyles.UserPaint) &&
        !this.Focused && this.TextLength == 0;

    #endregion
}

Answer 9

Private Sub randomSubName() Handles txtWatermark.Click
   txtWatermark.text = ""
End Sub

制作文本框的默认文本，无论你想要什么水印，我都假设在这个例子中你命名文本框txtWatermark

嘿，我是新人。很抱歉，如果我非常搞砸了帖子......我也不知道这是否有效......

WinForms中的水印TextBox

9 个答案: