public partial class WaterTextBox : TextBox{private readonly Label lblwaterText = new Label();public WaterTextBox(){InitializeComponent();lblwaterText.BorderStyle = BorderStyle.None;lblwaterText.Enabled = false;lblwaterText.BackColor = Color.White;lblwaterText.AutoSize = false;lblwaterText.Top = 1;lblwaterText.Left = 0;Controls.Add(lblwaterText);}[Category("扩展属性"), Description("显示的提示信息")]public string WaterText{get { return lblwaterText.Text; }set { lblwaterText.Text = value; }}public override string Text{set{if (value != string.Empty)lblwaterText.Visible = false;elselblwaterText.Visible = true;base.Text = value;}get { return base.Text; }}protected override void OnSizeChanged(EventArgs e){if (Multiline && (ScrollBars == ScrollBars.Vertical || ScrollBars == ScrollBars.Both))lblwaterText.Width = Width - 20;elselblwaterText.Width = Width;lblwaterText.Height = Height - 2;base.OnSizeChanged(e);}protected override void OnEnter(EventArgs e){lblwaterText.Visible = false;base.OnEnter(e);}protected override void OnLeave(EventArgs e){if (base.Text == string.Empty)lblwaterText.Visible = true;base.OnLeave(e);}}

public partial class WaterTextBox1 : TextBox{private String strEmptyValue = String.Empty;public WaterTextBox1(){InitializeComponent();processDefaultValue();}public String EmptyValue //记录空值的表现{get { return strEmptyValue; }set{if (base.Text == strEmptyValue)base.Text = value.Trim();strEmptyValue = value.Trim();processDefaultValue();}}public override string Text //覆盖Text属性{get { return base.Text.Trim() == strEmptyValue.Trim() ? String.Empty : base.Text.Trim(); }set{base.Text = value;processDefaultValue();}}protected override void OnVisibleChanged(EventArgs e){base.OnVisibleChanged(e);processDefaultValue();}protected override void OnMouseClick(MouseEventArgs e){base.OnMouseClick(e);if (base.Text == strEmptyValue){SelectAll();}}protected override void OnValidating(CancelEventArgs e) //覆盖TextBox验证处理{processDefaultValue();base.OnValidating(e);}private void processDefaultValue() //处理表现空值的方法{base.Text = base.Text.Trim().Length <= 0 ? strEmptyValue : base.Text.Trim();}}