Sam隨堂筆記

public partial class uTextBox : TextBox

{

    private string _tipText = string.Empty; //提示訊息

    public string TipText

    {

        get { return _tipText; }

        set { _tipText = value; Invalidate(); }

    }

    private Color _tipColor = SystemColors.Highlight; //訊息顏色

    public Color TipColor

    {

        get { return _tipColor; }

        set { _tipColor = value; Invalidate(); }

    }

    private Font _tipFont = DefaultFont; //訊息字型

    public Font TipFont

    {

        get { return _tipFont; }

        set { _tipFont = value; Invalidate(); }

    }

}

const int WM_PAINT = 0xF; //繪製的訊息

protected override void WndProc(ref Message m)

{

    base.WndProc(ref m);

    if (m.Msg == WM_PAINT && !string.IsNullOrEmpty(_tipText) && Text.Length == 0 && Enabled && !ReadOnly && !Focused) //判斷TextBox的狀態決定要不要顯示提示訊息

    {

        TextFormatFlags formatFlags = TextFormatFlags.Default; //使用原始設定的對齊方式來顯示提示訊息

        switch (TextAlign)

        {

            case HorizontalAlignment.Center:

                formatFlags = TextFormatFlags.HorizontalCenter;

                break;

            case HorizontalAlignment.Left:

                formatFlags = TextFormatFlags.Left;

                break;

            case HorizontalAlignment.Right:

                formatFlags = TextFormatFlags.Right;

                break;

        }

        TextRenderer.DrawText(Graphics.FromHwnd(Handle), _tipText, _tipFont, ClientRectangle, _tipColor, BackColor, formatFlags); //畫出提示訊息

    }

}