為什么從類庫項目添加dll文件時出現錯誤：錯誤Provider1上的錯誤？

Question

我使用此網站作為在這種情況下的textBox中創建自定義控件的示例：

自訂控制

在類庫項目中，我構建了項目，並且擁有dll文件。 然后在我的Windows Forms項目中，在Take框上，當我選擇dll文件時我確實選擇了項目，我看到它已添加到dll文件列表中，但我看不到它附近的這個紫色標志：

這是添加dll文件時Windows窗體項目的屏幕截圖。

加載后的dll左側為：ExtdTextBox，但靠近它的左側沒有此紫色符號。

然后，在form1設計器中，拖動后會看到文本框。

在底部的解決方案資源管理器的右側，您會看到我得到的錯誤：

errorProviler1上的錯誤

這是我添加到“類庫”項目中的類：

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
    }
}

類庫項目就像在網站示例中一樣，我在c＃> Windows> Windows窗體控件庫下創建了新項目

.net 4.5，因為我的Windows窗體項目我也想將dll添加到.net 4.5

Answer 1

這不是錯誤； 它是由ErrorProvider組件提供的名為Error的屬性。 該組件使您可以將錯誤消息與任何控件相關聯。