c# - 将占位符文本添加到文本框

Question

我正在寻找一种将占位符文本添加到文本框的方法，就像使用 html5 中的文本框一样。

即如果文本框没有文本，则添加文本Enter some text here，当用户单击它时，占位符文本消失并允许用户输入自己的文本，如果文本框失去焦点并且仍然没有文本，则占位符是添加回文本框。

score 105 · Accepted Answer

那不就是这样吗：

Textbox myTxtbx = new Textbox();
myTxtbx.Text = "Enter text here...";

myTxtbx.GotFocus += GotFocus.EventHandle(RemoveText);
myTxtbx.LostFocus += LostFocus.EventHandle(AddText);

public void RemoveText(object sender, EventArgs e)
{
    if (myTxtbx.Text == "Enter text here...") 
    {
     myTxtbx.Text = "";
    }
}

public void AddText(object sender, EventArgs e)
{
    if (string.IsNullOrWhiteSpace(myTxtbx.Text))
        myTxtbx.Text = "Enter text here...";
}

那只是伪代码，但概念就在那里。

score 103 · Accepted Answer

您可以使用它，它对我有用，并且是非常简单的解决方案。

    <Style x:Key="placeHolder" TargetType="{x:Type TextBox}" BasedOn="{StaticResource {x:Type TextBox}}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type TextBox}">
                    <Grid>
                        <TextBox Text="{Binding Path=Text,
                                                RelativeSource={RelativeSource TemplatedParent}, 
                                                Mode=TwoWay,
                                                UpdateSourceTrigger=PropertyChanged}"
                                 x:Name="textSource" 
                                 Background="Transparent" 
                                 Panel.ZIndex="2" />
                        <TextBox Text="{TemplateBinding Tag}" Background="{TemplateBinding Background}" Panel.ZIndex="1">
                            <TextBox.Style>
                                <Style TargetType="{x:Type TextBox}">
                                    <Setter Property="Foreground" Value="Transparent"/>
                                    <Style.Triggers>
                                        <DataTrigger Binding="{Binding Path=Text, Source={x:Reference textSource}}" Value="">
                                            <Setter Property="Foreground" Value="LightGray"/>
                                        </DataTrigger>
                                    </Style.Triggers>
                                </Style>
                            </TextBox.Style>
                        </TextBox>
                    </Grid>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

用法：

<TextBox Style="{StaticResource placeHolder}" Tag="Name of customer" Width="150" Height="24"/>

‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎‎

score 54 · Accepted Answer

除了处理焦点进入和焦点离开事件来设置和删除占位符文本之外，还可以使用 Windows SendMessage 函数将 EM_SETCUEBANNER消息发送到我们的文本框来为我们完成工作。

这可以通过两个简单的步骤来完成。首先，我们需要公开 WindowsSendMessage功能。

private 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);

然后只需使用我们的文本框的句柄、EM_SETCUEBANNER 的值和我们要设置的文本来调用该方法。

SendMessage(textBox1.Handle, EM_SETCUEBANNER, 0, "Username");
SendMessage(textBox2.Handle, EM_SETCUEBANNER, 0, "Password");

参考：为文本框设置占位符文本（提示文本）

score 26 · Accepted Answer

将此类添加到您的项目并构建您的解决方案。单击 Visual Studio 上的工具箱，您将看到一个名为 PlaceholderTextBox 的新文本框组件。删除表单设计上的当前文本框并替换为 PlaceHolderTextBox。

PlaceHolderTextBox 有一个属性 PlaceHolderText。设置您想要的任何文本并度过美好的一天:)

public class PlaceHolderTextBox : TextBox
{

    bool isPlaceHolder = true;
    string _placeHolderText;
    public string PlaceHolderText
    {
        get { return _placeHolderText; }
        set
        {
            _placeHolderText = value;
            setPlaceholder();
        }
    }

    public new string Text
    {
        get => isPlaceHolder ? string.Empty : base.Text;
        set => base.Text = value;
    }

    //when the control loses focus, the placeholder is shown
    private void setPlaceholder()
    {
        if (string.IsNullOrEmpty(base.Text))
        {
            base.Text = PlaceHolderText;
            this.ForeColor = Color.Gray;
            this.Font = new Font(this.Font, FontStyle.Italic);
            isPlaceHolder = true;
        }
    }

    //when the control is focused, the placeholder is removed
    private void removePlaceHolder()
    {

        if (isPlaceHolder)
        {
            base.Text = "";
            this.ForeColor = System.Drawing.SystemColors.WindowText;
            this.Font = new Font(this.Font, FontStyle.Regular);
            isPlaceHolder = false;
        }
    }
    public PlaceHolderTextBox()
    {
        GotFocus += removePlaceHolder;
        LostFocus += setPlaceholder;
    }

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

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

score 22 · Accepted Answer

这不是我的代码，但我经常使用它，而且效果很好……仅限 XAML

<TextBox x:Name="Textbox" Height="23" Margin="0,17,18.8,0" TextWrapping="Wrap" Text="" VerticalAlignment="Top" HorizontalAlignment="Right" ></TextBox>

<TextBlock x:Name="Placeholder" IsHitTestVisible="False" TextWrapping="Wrap" Text="Placeholder Text" VerticalAlignment="Top" Margin="0,20,298.8,0" Foreground="DarkGray" HorizontalAlignment="Right" Width="214">
  <TextBlock.Style>
    <Style TargetType="{x:Type TextBlock}">
      <Setter Property="Visibility" Value="Collapsed"/>
      <Style.Triggers>
        <DataTrigger Binding="{Binding Text, ElementName=Textbox}" Value="">
          <Setter Property="Visibility" Value="Visible"/>
        </DataTrigger>
      </Style.Triggers>
    </Style>
  </TextBlock.Style>
</TextBlock>

score 10 · Accepted Answer

救援的附加属性：

public static class TextboxExtensions
{
    public static readonly DependencyProperty PlaceholderProperty = 
        DependencyProperty.RegisterAttached(
            "Placeholder", 
            typeof(string), 
            typeof(TextboxExtensions), 
            new PropertyMetadata(default(string), propertyChangedCallback: PlaceholderChanged)
            );

    private static void PlaceholderChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs args)
    {
        var tb = dependencyObject as TextBox;

        if (tb == null)
            return;

        tb.LostFocus -= OnLostFocus;
        tb.GotFocus -= OnGotFocus;

        if (args.NewValue != null)
        {
            tb.GotFocus += OnGotFocus;
            tb.LostFocus += OnLostFocus;
        }

        SetPlaceholder(dependencyObject, args.NewValue as string);

        if (!tb.IsFocused)
            ShowPlaceholder(tb);
    }

    private static void OnLostFocus(object sender, RoutedEventArgs routedEventArgs)
    {
        ShowPlaceholder(sender as TextBox);
    }

    private static void OnGotFocus(object sender, RoutedEventArgs routedEventArgs)
    {
        HidePlaceholder(sender as TextBox);
    }

    [AttachedPropertyBrowsableForType(typeof(TextBox))]
    public static void SetPlaceholder(DependencyObject element, string value)
    {
        element.SetValue(PlaceholderProperty, value);
    }

    [AttachedPropertyBrowsableForType(typeof(TextBox))]
    public static string GetPlaceholder(DependencyObject element)
    {
        return (string)element.GetValue(PlaceholderProperty);
    }

    private static void ShowPlaceholder(TextBox textBox)
    {
        if (string.IsNullOrWhiteSpace(textBox.Text))
        {
            textBox.Text = GetPlaceholder(textBox);
        }
    }

    private static void HidePlaceholder(TextBox textBox)
    {
        string placeholderText = GetPlaceholder(textBox);

        if (textBox.Text == placeholderText)
            textBox.Text = string.Empty;
    }
}

用法：

<TextBox Text="hi" local:TextboxExtensions.Placeholder="Hello there"></TextBox>

score 7 · Accepted Answer

虽然使用EM_SETCUEBANNER消息可能是最简单的，但我不喜欢的一件事是当控件获得焦点时占位符文本会消失。当我填写表格时，这是我的一个小烦恼。我必须单击它才能记住该字段的用途。

因此，这是 WinForms 的另一种解决方案。它覆盖Label在控件的顶部，仅当用户开始键入时它才会消失。

这当然不是防弹的。它接受 any Control，但我只用TextBox. 它可能需要修改才能与某些控件一起使用。如果您需要在特定情况下对其进行一些修改，该方法将返回Label控件，但这可能永远不需要。

像这样使用它：

SetPlaceholder(txtSearch, "Type what you're searching for");

这是方法：

/// <summary>
/// Sets placeholder text on a control (may not work for some controls)
/// </summary>
/// <param name="control">The control to set the placeholder on</param>
/// <param name="text">The text to display as the placeholder</param>
/// <returns>The newly-created placeholder Label</returns>
public static Label SetPlaceholder(Control control, string text) {
    var placeholder = new Label {
        Text = text,
        Font = control.Font,
        ForeColor = Color.Gray,
        BackColor = Color.Transparent,
        Cursor = Cursors.IBeam,
        Margin = Padding.Empty,

        //get rid of the left margin that all labels have
        FlatStyle = FlatStyle.System,
        AutoSize = false,

        //Leave 1px on the left so we can see the blinking cursor
        Size = new Size(control.Size.Width - 1, control.Size.Height),
        Location = new Point(control.Location.X + 1, control.Location.Y)
    };

    //when clicking on the label, pass focus to the control
    placeholder.Click += (sender, args) => { control.Focus(); };

    //disappear when the user starts typing
    control.TextChanged += (sender, args) => {
        placeholder.Visible = string.IsNullOrEmpty(control.Text);
    };

    //stay the same size/location as the control
    EventHandler updateSize = (sender, args) => {
        placeholder.Location = new Point(control.Location.X + 1, control.Location.Y);
        placeholder.Size = new Size(control.Size.Width - 1, control.Size.Height);
    };

    control.SizeChanged += updateSize;
    control.LocationChanged += updateSize;

    control.Parent.Controls.Add(placeholder);
    placeholder.BringToFront();

    return placeholder;
}

score 5 · Accepted Answer

基于 ExceptionLimeCat 的回答，改进：

Color farbe;
string ph = "Placeholder-Text";

private void Form1_Load(object sender, EventArgs e)
{
    farbe = myTxtbx.ForeColor;
    myTxtbx.GotFocus += RemoveText;
    myTxtbx.LostFocus += AddText;
    myTxtbx.Text = ph;
}


public void RemoveText(object sender, EventArgs e)
{
    myTxtbx.ForeColor = farbe;
    if (myTxtbx.Text == ph)
        myTxtbx.Text = "";
}

public void AddText(object sender, EventArgs e)
{
    if (String.IsNullOrWhiteSpace(myTxtbx.Text))
    {
        myTxtbx.ForeColor = Color.Gray;
        myTxtbx.Text = ph;
    }
}

score 3 · Accepted Answer

这意味着您有一个按钮，可让您执行操作，例如登录或其他操作。在执行操作之前，请检查文本框是否已填写。如果没有，它将替换文本

 private void button_Click(object sender, EventArgs e)
 {
     string textBoxText = textBox.Text;

     if (String.IsNullOrWhiteSpace(textBoxText))
     {
         textBox.Text = "Fill in the textbox";
     }
 }

 private void textBox_Enter(object sender, EventArgs e)
 {
     TextBox currentTextbox = sender as TextBox;
     if (currentTextbox.Text == "Fill in the textbox")
     {
         currentTextbox.Text = "";
     }
 }

这有点俗气，但是检查文本以获取您提供的值是我能做的最好的 atm，而不擅长 c# 以获得更好的解决方案。

score 3 · Accepted Answer

您可以获取默认值Template，通过覆盖 a 对其进行修改TextBlock，并使用 aStyle添加以正确状态隐藏和显示它的触发器。

score 3 · Accepted Answer

我知道这是一个旧线程，但 .NET Core 和 .NET 5.0 已经实现了该TextBox.PlaceholderText属性。

https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.textbox.placeholdertext?view=net-5.0

score 2 · Accepted Answer

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;

namespace App_name
{
   public class CustomTextBox : TextBox
    {
        private string Text_ = "";
        public CustomTextBox() : base()
        {}

        public string setHint
        {
            get { return Text_; }
            set { Text_ = value; }
        }
        protected override void OnGotFocus(RoutedEventArgs e)
        {
            base.OnGotFocus(e);
            if (Text_.Equals(this.Text))
                this.Clear();
        }
        protected override void OnLostFocus(RoutedEventArgs e)
        {
            base.OnLostFocus(e);
            if (String.IsNullOrWhiteSpace(this.Text))
                this.Text = Text_;
        }
    }
}
>    xmlns:local="clr-namespace:app_name"
>  <local:CustomTextBox
>                 x:Name="id_number_txt"
>                 Width="240px"
>                 Height="auto"/>

score 2 · Accepted Answer

这是 texbox 的扩展方法。只需以编程方式添加占位符文本：

myTextBox.AddPlaceholderText("Hello World!");

扩展方法：

public static void AddPlaceholderText(this TextBox textBox, string placeholderText)
        {
            if (string.IsNullOrWhiteSpace(textBox.Text))
                textBox.Text = placeholderText;
            textBox.SetResourceReference(Control.ForegroundProperty,
                textBox.Text != placeholderText
                    ? "SystemControlForegroundBaseHighBrush"
                    : "SystemControlForegroundBaseMediumBrush");
            var ignoreSelectionChanged = false;
            textBox.SelectionChanged += (sender, args) =>
            {
                if (ignoreSelectionChanged) { ignoreSelectionChanged = false; return; }
                if (textBox.Text != placeholderText) return;
                ignoreSelectionChanged = true;
                textBox.Select(0, 0);
            };
            var lastText = textBox.Text;
            var ignoreTextChanged = false;
            textBox.TextChanged += (sender, args) =>
            {
                if (ignoreTextChanged) { ignoreTextChanged = false; return; }
                if (string.IsNullOrWhiteSpace(textBox.Text))
                {
                    ignoreTextChanged = true;
                    textBox.Text = placeholderText;
                    textBox.Select(0, 0);
                }
                else if (lastText == placeholderText)
                {
                    ignoreTextChanged = true;
                    textBox.Text = textBox.Text.Substring(0, 1);
                    textBox.Select(1, 0);
                }

                textBox.SetResourceReference(Control.ForegroundProperty,
                    textBox.Text != placeholderText
                        ? "SystemControlForegroundBaseHighBrush"
                        : "SystemControlForegroundBaseMediumBrush");
                lastText = textBox.Text;
            };
        }

快乐编码，BierDav

score 2 · Accepted Answer

在这里，我提出了受@Kemal Karadag 启发的解决方案。

我注意到这里发布的每个解决方案都依赖于焦点，

虽然我希望我的占位符是 Google Chrome 中标准 HTML 占位符的精确克隆。

当框聚焦时，而不是隐藏/显示占位符，

我根据框的文本长度隐藏/显示占位符：

如果框为空，则显示占位符，如果您在框中键入，则占位符消失。

由于它继承自标准文本框，因此您可以在工具箱中找到它！

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

public class PlaceHolderTextBox : TextBox
{
    private bool isPlaceHolder = true;
    private string placeHolderText;

    public string PlaceHolderText
    {
        get { return placeHolderText; }
        set
        {
            placeHolderText = value;
            SetPlaceholder();
        }
    }

    public PlaceHolderTextBox()
    {
        TextChanged += OnTextChanged;
    }

    private void SetPlaceholder()
    {
        if (!isPlaceHolder)
        {
            this.Text = placeHolderText;
            this.ForeColor = Color.Gray;
            isPlaceHolder = true;
        }
    }

    private void RemovePlaceHolder()
    {
        if (isPlaceHolder)
        {
            this.Text = this.Text[0].ToString(); // Remove placeHolder text, but keep the character we just entered
            this.Select(1, 0); // Place the caret after the character we just entered
            this.ForeColor = System.Drawing.SystemColors.WindowText;
            isPlaceHolder = false;
        }
    }

    private void OnTextChanged(object sender, EventArgs e)
    {
        if (this.Text.Length == 0)
        {
            SetPlaceholder();
        }
        else
        {
            RemovePlaceHolder();
        }
    }
}

score 1 · Accepted Answer

我想出了一种对我有用的方法，但这只是因为我愿意使用文本框名称作为占位符。见下文。

public TextBox employee = new TextBox();

private void InitializeHomeComponent()
{
    //
    //employee
    //
    this.employee.Name = "Caller Name";
    this.employee.Text = "Caller Name";
    this.employee.BackColor = System.Drawing.SystemColors.InactiveBorder;
    this.employee.Location = new System.Drawing.Point(5, 160);
    this.employee.Size = new System.Drawing.Size(190, 30);
    this.employee.TabStop = false;
    this.Controls.Add(employee);
    // I loop through all of my textboxes giving them the same function
    foreach (Control C in this.Controls)
    {
        if (C.GetType() == typeof(System.Windows.Forms.TextBox))
        {
            C.GotFocus += g_GotFocus;
            C.LostFocus += g_LostFocus;
        }
     }
 }

    private void g_GotFocus(object sender, EventArgs e)
    {
        var tbox = sender as TextBox;
        tbox.Text = "";
    }

    private void g_LostFocus(object sender, EventArgs e)
    {
        var tbox = sender as TextBox;
        if (tbox.Text == "")
        {
            tbox.Text = tbox.Name;
        }
    }

score 0 · Accepted Answer

试试下面的代码：

<TextBox x:Name="InvoiceDate" Text="" Width="300"  TextAlignment="Left" Height="30" Grid.Row="0" Grid.Column="3" Grid.ColumnSpan="2" />
                    <TextBlock IsHitTestVisible="False" Text="Men att läsa" Width="300"  TextAlignment="Left" Height="30" Grid.Row="0" Grid.Column="3" Grid.ColumnSpan="2" Padding="5, 5, 5, 5"  Foreground="LightGray">
                        <TextBlock.Style>
                            <Style TargetType="{x:Type TextBlock}">
                                <Setter Property="Visibility" Value="Collapsed"/>
                                <Style.Triggers>
                                    <DataTrigger Binding="{Binding Text, ElementName=InvoiceDate}" Value="">
                                        <Setter Property="Visibility" Value="Visible"/>
                                    </DataTrigger>
                                    <DataTrigger Binding="{Binding ElementName=InvoiceDate, Path=IsFocused}" Value="True">
                                        <Setter Property="Visibility" Value="Collapsed"/>
                                    </DataTrigger>

                                </Style.Triggers>
                            </Style>
                        </TextBlock.Style>
                    </TextBlock>

score 0 · Accepted Answer

您也可以在单击鼠标时执行此操作，假设您的占位符文本是“User_Name”

 private void textBox1_MouseClick(object sender, MouseEventArgs e)
 {
     if(textBox1.Text == "User_Name")
          textBox1.Text = "";
 }

score 0 · Accepted Answer

你也可以这样试试。。

调用函数

TextboxPlaceHolder(this.textBox1, "YourPlaceHolder");

写这个函数

private void TextboxPlaceHolder(Control control, string PlaceHolderText)
{
        control.Text = PlaceHolderText;
        control.GotFocus += delegate (object sender, EventArgs args)
        {
            if (cusmode == false)
            {
                control.Text = control.Text == PlaceHolderText ? string.Empty : control.Text;
                //IF Focus TextBox forecolor Black
                control.ForeColor = Color.Black;
            }
        };

        control.LostFocus += delegate (object sender, EventArgs args)
        {
            if (string.IsNullOrWhiteSpace(control.Text) == true)
            {
                control.Text = PlaceHolderText;
                //If not focus TextBox forecolor to gray
                control.ForeColor = Color.Gray;
            }

        };
}

score 0 · Accepted Answer

    public void Initialize()
    {
        SetPlaceHolder(loginTextBox, " Логин ");
        SetPlaceHolder(passwordTextBox, " Пароль ");
    }

    public void SetPlaceHolder(Control control, string PlaceHolderText)
    {
        control.Text = PlaceHolderText;
        control.GotFocus += delegate(object sender, EventArgs args) {
            if (control.Text == PlaceHolderText)
            {
                control.Text = "";
            }
        };
        control.LostFocus += delegate(object sender, EventArgs args){
            if (control.Text.Length == 0)
            {
                control.Text = PlaceHolderText;
            }
        };
    }

score 0 · Accepted Answer

有更好的解决方案，但最简单的解决方案在这里：将文本框文本设置为所需的字符串，然后创建一个删除文本的函数，让该函数在文本框焦点输入事件上触发

score 0 · Accepted Answer

我写了一个可重用的自定义控件，也许它可以帮助需要在他的项目中实现多个占位符文本框的人。
这是带有实例实现示例的自定义类，您可以通过将此代码粘贴到使用 VS 的新 winforms 项目中轻松测试：

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();
            }
        }
    }
}

score 0 · Accepted Answer

让我们用 PlcaeHoldText 和 PlaceHoldBackround 扩展 TextBox。我从我的项目中删除了一些代码。

告别网格或画布！

<TextBox x:Class="VcpkgGui.View.PlaceHoldedTextBox"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:local="clr-namespace:VcpkgGui.View"
             mc:Ignorable="d"
             Name="placeHoldTextBox"
             TextAlignment="Left"
         >
    <TextBox.Resources>
        <local:FrameworkWidthConverter x:Key="getElemWidth"/>
        <local:FrameworkHeightConverter x:Key="getElemHeight"/>
        <VisualBrush x:Key="PlaceHoldTextBrush" TileMode="None" Stretch="None" AlignmentX="Left" AlignmentY="Center" Opacity="1">
            <VisualBrush.Visual>
                <Border Background="{Binding ElementName=placeHoldTextBox, Path=PlaceHoldBackground}"
                        BorderThickness="0"
                        Margin="0,0,0,0"
                        Width="{Binding Mode=OneWay, ElementName=placeHoldTextBox, Converter={StaticResource getElemWidth}}"
                        Height="{Binding Mode=OneWay, ElementName=placeHoldTextBox, Converter={StaticResource getElemHeight}}"
                        >
                    <Label Content="{Binding ElementName=placeHoldTextBox, Path=PlaceHoldText}"
                           Background="Transparent"
                           Foreground="#88000000"
                           HorizontalAlignment="Stretch"
                           VerticalAlignment="Stretch"
                           HorizontalContentAlignment="Left"
                           VerticalContentAlignment="Center"
                           ClipToBounds="True"
                           Padding="0,0,0,0"
                           FontSize="14"
                           FontStyle="Normal"
                           Opacity="1"/>
                </Border>
            </VisualBrush.Visual>
        </VisualBrush>
    </TextBox.Resources>
    <TextBox.Style>
        <Style TargetType="TextBox">
            <Style.Triggers>
                <Trigger Property="Text" Value="{x:Null}">
                    <Setter Property="Background"  Value="{StaticResource PlaceHoldTextBrush}"/>
                </Trigger>
                <Trigger Property="Text" Value="">
                    <Setter Property="Background"  Value="{StaticResource PlaceHoldTextBrush}"/>
                </Trigger>
            </Style.Triggers>
        </Style>
    </TextBox.Style>
</TextBox>

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace VcpkgGui.View
{
    /// <summary>
    /// PlaceHoldedTextBox.xaml 的交互逻辑
    /// </summary>
    public partial class PlaceHoldedTextBox : TextBox
    {

        public string PlaceHoldText
        {
            get { return (string)GetValue(PlaceHoldTextProperty); }
            set { SetValue(PlaceHoldTextProperty, value); }
        }

        // Using a DependencyProperty as the backing store for PlaceHolderText.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty PlaceHoldTextProperty =
            DependencyProperty.Register("PlaceHoldText", typeof(string), typeof(PlaceHoldedTextBox), new PropertyMetadata(string.Empty));



        public Brush PlaceHoldBackground
        {
            get { return (Brush)GetValue(PlaceHoldBackgroundProperty); }
            set { SetValue(PlaceHoldBackgroundProperty, value); }
        }

        public static readonly DependencyProperty PlaceHoldBackgroundProperty =
            DependencyProperty.Register(nameof(PlaceHoldBackground), typeof(Brush), typeof(PlaceHoldedTextBox), new PropertyMetadata(Brushes.White));

        public PlaceHoldedTextBox() :base()
        {
            InitializeComponent();
        }
    }

    [ValueConversion(typeof(FrameworkElement), typeof(double))]
    internal class FrameworkWidthConverter : System.Windows.Data.IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if(value is FrameworkElement elem)
                return double.IsNaN(elem.Width) ? elem.ActualWidth : elem.Width;
            else
                return DependencyProperty.UnsetValue;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return DependencyProperty.UnsetValue;
        }
    }

    [ValueConversion(typeof(FrameworkElement), typeof(double))]
    internal class FrameworkHeightConverter : System.Windows.Data.IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (value is FrameworkElement elem)
                return double.IsNaN(elem.Height) ? elem.ActualHeight : elem.Height;
            else
                return DependencyProperty.UnsetValue;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return DependencyProperty.UnsetValue;
        }
    }

}

score 0 · Accepted Answer

我没有使用 TextBox 的 .Text 属性，而是用占位符覆盖了一个 TextBlock。我无法使用 .Text 属性，因为它已绑定到事件。

XAML：

<Canvas Name="placeHolderCanvas">
    <TextBox  AcceptsReturn="True" Name="txtAddress" Height="50" Width="{Binding ActualWidth, ElementName=placeHolderCanvas}"
              Tag="Please enter your address"/>
</Canvas>

VB.NET

Public Shared Sub InitPlaceholder(canvas As Canvas)
    Dim txt As TextBox = canvas.Children.OfType(Of TextBox).First()
    Dim placeHolderLabel = New TextBlock() With {.Text = txt.Tag,
                                                 .Foreground = New SolidColorBrush(Color.FromRgb(&H77, &H77, &H77)),
                                                 .IsHitTestVisible = False}
    Canvas.SetLeft(placeHolderLabel, 3)
    Canvas.SetTop(placeHolderLabel, 1)
    canvas.Children.Add(placeHolderLabel)
    AddHandler txt.TextChanged, Sub() placeHolderLabel.Visibility = If(txt.Text = "", Visibility.Visible, Visibility.Hidden)
End Sub

结果：

score -1 · Accepted Answer

-1

txtUsuario.Attributes.Add("placeholder", "Texto");

于 2015-08-28T14:04:45.283 回答

score -1 · Accepted Answer

WindowsForms TextBox 控件的非常有效的解决方案。（不确定 XAML）。

这也适用于多行模式。

可能它可以扩展到其他控件，例如 ComboBox 控件（未选中）

score -2 · Accepted Answer

奇迹般有效。

public class WTextBox : TextBox
{
    private string _placeholder;


    [Category("Appearance")]
    public string Placeholder
    {
        get { return _placeholder; }
        set
        {
            _placeholder = value ?? string.Empty;
            Invalidate();
        }
    }

    public WTextBox()
    {
        _placeholder = string.Empty;
    }

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

        if (m.Msg != 0xF || Focused || !string.IsNullOrEmpty(Text) || string.IsNullOrWhiteSpace(_placeholder))
        {
            return;
        }

        using (var g = CreateGraphics())
        {
            TextRenderer.DrawText(g, _placeholder, Font, ClientRectangle, SystemColors.GrayText, BackColor, TextFormatFlags.Left);
        }
    }
}

c# - 将占位符文本添加到文本框

26 回答 26

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