为什么从类库项目中添加dll文件时出现错误：错误提供者1错误？

Question

我使用此网站作为在此textBox中创建自定义控件的示例：

Custom Control

在类库项目中，我构建了项目，我有了dll文件。 然后在我的Windows窗体项目中，当我选择dll文件时，我确实选择了项目，我看到它被添加到dll文件列表中，但我没有看到它附近的紫色标志：

这是添加dll文件时Windows窗体项目的屏幕截图。

在加载它之后的dll左边调用：ExtdTextBox但是在它附近就没有这个紫色标志。

然后在form1设计器中，拖动它后会看到textBox。

在底部解决方案资源管理器的右侧，您会看到我得到的错误：

errorProviler1上的错误

这是我添加到我的类库项目的类：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.ComponentModel;
using System.Drawing;

namespace CustomControl
{
    public class ExtdTextBox : TextBox
    {
        #region Member Variables
        Color waterMarkColor = Color.Gray;
        Color forecolor;
        Font font;
        Font waterMarkFont;
        string waterMarkText = "Your Text Here";
        #endregion 
        #region Constructor
        public ExtdTextBox()
        {
            base.Text = this.waterMarkText;
            this.forecolor = this.ForeColor;
            this.ForeColor = this.waterMarkColor;
           this.font = this.Font;
            //event handlers
            this.TextChanged += new EventHandler(ExtdTextBox_TextChanged);
            this.KeyPress += new KeyPressEventHandler(ExtdTextBox_KeyPress);
            this.LostFocus += new EventHandler(ExtdTextBox_TextChanged);
        }
        #endregion
        #region Event Handler Methods
        void ExtdTextBox_TextChanged(object sender, EventArgs e)
        {
            if (!string.IsNullOrEmpty(this.Text))
            {
                this.ForeColor = this.forecolor;
                this.Font = this.font;
            }
            else
            {
                this.TextChanged -= new EventHandler(ExtdTextBox_TextChanged);
                base.Text = this.waterMarkText;
                this.TextChanged += new EventHandler(ExtdTextBox_TextChanged);
                this.ForeColor = this.waterMarkColor;
                this.Font = this.waterMarkFont;
            }
        }
       void ExtdTextBox_KeyPress(object sender, KeyPressEventArgs e)
        {
            string str = base.Text.Replace(this.waterMarkText, "");
            this.TextChanged -= new EventHandler(ExtdTextBox_TextChanged);
            this.Text = str;
            this.TextChanged += new EventHandler(ExtdTextBox_TextChanged);
        }
        #endregion
        #region User Defined Properties
        /// <summary>
        /// Property to set/get Watermark color at design/runtime
        /// </summary>
        [Browsable(true)]
        [Category("Extended Properties")]
       [Description("sets Watermark color")]
        [DisplayName("WaterMark Color")]
        public Color WaterMarkColor
        {
            get
            {
                return this.waterMarkColor;
            }
            set
            {
                this.waterMarkColor = value;
                base.OnTextChanged(new EventArgs());
            }
        }
        [Browsable(true)]
        [Category("Extended Properties")]
        [Description("sets TextBox text")]
        [DisplayName("Text")]
        /// <summary>
        /// Property to get Text at runtime(hides base Text property)
        /// </summary>
        public new string Text
        {
            get
            {
                //required for validation for Text property
                return base.Text.Replace(this.waterMarkText, string.Empty);
            }
            set
            {
                base.Text = value;
            }
        }
        [Browsable(true)]
        [Category("Extended Properties")]
        [Description("sets WaterMark font")]
        [DisplayName("WaterMark Font")]
        /// <summary>
        /// Property to get Text at runtime(hides base Text property)  
      /// </summary>
        public Font WaterMarkFont
        {
            get
            {
                //required for validation for Text property
                return this.waterMarkFont;
            }
            set
            {
                this.waterMarkFont = value;
                this.OnTextChanged(new EventArgs());
            }
        }
        /// <summary>
        ///  Property to set/get Watermark text at design/runtime
        /// </summary>
        [Browsable(true)]
        [Category("Extended Properties")]
        [Description("sets Watermark Text")]
        [DisplayName("WaterMark Text")]
        public string WaterMarkText
        {
            get
            {
                return this.waterMarkText;
            }
            set
            {
                this.waterMarkText = value;
                base.OnTextChanged(new EventArgs());
            }
        }
        #endregion
    }
}

类库项目就像我在c＃＆gt;下创建新项目的网站示例一样窗户＆gt; windows窗体控件库

.net 4.5，因为我的Windows窗体项目我想要添加dll也是.net 4.5

Answer 1

这不是错误;它是ErrorProvider组件提供的名为Error的属性。该组件允许您将错误消息与任何控件相关联。