在用户将文本输入TextBox 之前显示“Type here to ...”是当今众所周知的可用性功能。如何在 C# 中实现这一功能？
我的想法是覆盖OnTextChanged，但是处理文本从“在此处输入”的变化的逻辑有点棘手......
在初始化时显示“在此处输入”并在第一次输入时将其删除很容易，但我想在每次输入的文本变为空时显示消息。
【问题讨论】：
对我有用的东西：
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;
}
};
其中bool waterMarkActive 是类成员变量，textBox 是TextBox。不过这可能应该被封装:) 这种方法可能存在一些问题，但我目前不知道有任何问题。
我最近发现 Windows 支持文本框中的水印；它们被称为提示横幅（参见here）。很容易实现：
// 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.");
其中textBox 是TextBox 的一个实例，0x1501 是Windows 消息EM_SETCUEBANNER 的代码，wParam 可以是TRUE（非零）或FALSE（零)，lParam 是您要显示的水印。 wParam 指示何时应显示提示横幅；如果设置为TRUE，那么即使控件有焦点也会显示提示横幅。
【讨论】：
您正在寻找的是带有“水印”的文本框。
有一个 C# here 的示例实现，全部归功于 Wael Alghool。
他的代码的相关部分是：
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();
}
}
}
}
【讨论】：
根据@Pooven 的回答（谢谢！），我创建了这个类。对我有用。
/// <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();
}
}
【讨论】：
[DllImport("user32.dll", CharSet = CharSet.Auto)]
private static extern Int32 SendMessage(IntPtr hWnd, int msg, int wParam, [MarshalAs(UnmanagedType.LPWStr)]string lParam);
const int EM_SETCUEBANNER = 0x1501;
public Form1()
{
InitializeComponent();
SendMessage(textBox1.Handle, EM_SETCUEBANNER, 1, "Username");
SendMessage(textBox2.Handle, EM_SETCUEBANNER, 1, "Password");
}
【讨论】：
我这个学期刚开始学习 C#，所以我不是专家，但这对我有用： （这是使用windows窗体）
private void Form1_Load(object sender, EventArgs e)
{
textBox1.SelectionStart = 0; //This keeps the text
textBox1.SelectionLength = 0; //from being highlighted
textBox1.ForeColor = Color.Gray;
}
private void textBox_MouseMove(object sender, MouseEventArgs e)
{
Cursor.Current = Cursors.IBeam; //Without this the mouse pointer shows busy
}
private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
if (textBox1.Text.Equals("Type here...") == true)
{
textBox1.Text = "";
textBox1.ForeColor = Color.Black;
}
}
private void textBox1_KeyUp(object sender, KeyEventArgs e)
{
if (textBox1.Text.Equals(null) == true || textBox1.Text.Equals("") == true)
{
textBox1.Text = "Type here...";
textBox1.ForeColor = Color.Gray;
}
}
【讨论】：
产生与 HTML 水印相似的输出
这是我的文本框“水印”或“预览”文本的代码 - 效果很好！使用 Windows 窗体应用程序。
注意：这个例子有 3 个文本框，每个文本框都有下面的方法分别用于“鼠标离开”事件和“鼠标进入”事件。
private void textBoxFav_Leave(object sender, EventArgs e) {
TextBox textbox = (TextBox)sender;
if (String.IsNullOrWhiteSpace(textbox.Text)) {
textbox.ForeColor = Color.Gray;
if (textbox.Name == "textBoxFavFood") {
textbox.Text = "Favorite Food";
}
else if (textbox.Name == "textBoxFavDrink") {
textbox.Text = "Favorite Drink";
}
else if (textbox.Name == "textBoxFavDesert") {
textbox.Text = "Favorite Desert";
}
}
else {
textbox.ForeColor = Color.Black;
}
}
private void textBoxFav_Enter(object sender, EventArgs e) {
TextBox textbox = (TextBox)sender;
if (textbox.Text == "Favorite Food" || textbox.Text == "Favorite Drink" || textbox.Text == "Favorite Desert") {
textbox.Text = "";
textbox.ForeColor = Color.Black;
}
}
【讨论】：
处理失去焦点事件，如果属性 Text 为空，则使用默认字符串填充它。
【讨论】：
如果这是 ASP.NET（而不是 winforms），您可以这样做：
如果您使用的是 jQuery，请将其添加到准备好的文档中（或者您初始化页面）：
var $textbox = $("textbox selector"); // assumes you select a single text box
if ($textbox.val() == "") {
$textbox.val("Type here to...");
$textbox.one('focus', function() {
$(this).attr('value', '');
});
}
如果要选择多个文本框，则需要进行一些小的重构（将 if 语句放在元素上的 each 内）。
【讨论】：
在 C# 的最后一个版本中，TextBox 具有属性 PlaceholderText，它可以正常工作。所以你只需要设置“Type here...”作为这个属性的值。
【讨论】：
根据 Ahmed Soliman Flasha 的回答，使用以下课程：
public class TextBoxHint : TextBox
{
string _hint;
[Localizable(true)]
public string Hint
{
get { return _hint; }
set { _hint = value; OnHintChanged(); }
}
protected virtual void OnHintChanged()
{
SendMessage(this.Handle, EM_SETCUEBANNER, 1, _hint);
}
const int EM_SETCUEBANNER = 0x1501;
[DllImport("user32.dll", CharSet = CharSet.Auto)]
private static extern Int32 SendMessage(IntPtr hWnd, int msg, int wParam, [MarshalAs(UnmanagedType.LPWStr)]string lParam);
}
【讨论】：
您可以将字符串“Type here”绘制到文本框背景直到它为空
【讨论】：
如果这是针对 ASP.NET 的，那么您可以尝试TextBoxWatermark。
如果这是用于 Windows 窗体，则已在 SO 中回答 here。
【讨论】：
为什么要使用 OnTextChanged？ 我建议在 TextBox 获得焦点时删除文本“在此处输入”。 当控件失去焦点并且没有输入文本时，您可以再次显示文本。
同样的结果，不需要复杂的逻辑。
【讨论】：
如果您想避免控件调整大小问题和数据绑定问题并使代码更简单（好吧，这是有问题的），您可以只使用标签并切换它的可见性。那么
private void FilterComboBox_GotFocus(object sender, EventArgs e)
{
FilterWatermarkLabel.Visible = false;
}
private void FilterComboBox_LostFocus(object sender, EventArgs e)
{
if (!FilterWatermarkLabel.Visible && string.IsNullOrEmpty(FilterComboBox.Text))
{
FilterWatermarkLabel.Visible = true;
}
}
这里有另一种处理图像并避免数据绑定问题的方法 https://msdn.microsoft.com/en-us/library/bb613590(v=vs.100).aspx
【讨论】：
基于@Joel 的回答。我修复了他的课程（感谢基础！）
/// <summary>
/// A textbox that supports a watermak hint.
/// Based on: https://stackoverflow.com/a/15232752
/// </summary>
public class WatermarkTextBox : TextBox
{
/// <summary>
/// The text that will be presented as the watermak hint
/// </summary>
private string _watermarkText;
/// <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;
/// <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 = _watermarkActive;
this.Text = _watermarkText;
}
protected override void OnCreateControl()
{
base.OnCreateControl();
if (this.WatermarkActive)
CheckWatermark();
}
protected override void OnGotFocus(EventArgs e)
{
base.OnGotFocus(e);
CheckWatermark();
}
protected override void OnLostFocus(EventArgs e)
{
base.OnLostFocus(e);
CheckWatermark();
}
public void CheckWatermark()
{
if ((this.WatermarkActive) && String.IsNullOrWhiteSpace(this.Text))
{
ForeColor = Color.Gray;
this.Text = _watermarkText;
}
else if ((this.WatermarkActive) && (!String.IsNullOrWhiteSpace(this.Text)))
{
if (this.Text == _watermarkText)
this.Text = "";
ForeColor = Color.Black;
}
else
ForeColor = Color.Black;
}
}
【讨论】：
在用户将文本输入文本框之前显示“在此处键入...”是当今众所周知的可用性功能。如何在 C# 中实现这一功能？
将 textbox.text 设置为“Type here to ...”
创建一个事件，比如 box_click()
-->把这段代码放到你的方法中
private void box_Click(object sender, EventArgs e)
{
Textbox b = (Textbox)sender;
b.Text = null;
}
现在将此方法分配给文本框的“Enter”事件（可能是一个或多个）
【讨论】：