Multi-color DropDownList using C# - 顏色挑選器
參考: Multi-color DropDownList using C# By Fuad Bin Omar
之前在做案子的時候，我也有利用 DropDownList 抓取 System.Drawing.KnownColor 列舉型態，並配合 Enum.GetNames(typeof(KnownColor)) 抓取系統顏色清單，做成顏色挑選器供使用者挑選。但是卻沒有參考連結中，Fuad Bin Omar 寫得那麼完善，而且我當時也沒有考慮系統環境顏色必須忽略，例如【Active Border】。
幸好，今日在 MSDN 技術社群討論區 也有提到類似的問題，讓我搜尋到 Fuad Bin Omar 也有寫出這樣的顏色挑選器。剛剛，把 Fuad Bin Omar 的顏色挑選氣作一些調整，主要顯示顏色的部分加入 CSS，讓深色系的顏色用白色的文字來呈現顏色名稱；淺色系則使用黑色文字。比較如下：(右圖是修改後)
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MultiColorDDlist.aspx 程式碼，如下：
1: <%@ Page Language="C#" AutoEventWireup="true" CodeFile="MultiColorDDlist.aspx.cs"
2: Inherits="MultiColorDDlist" %>
3:
4: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
5: "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
6: <html xmlns="http://www.w3.org/1999/xhtml">
7: <head runat="server">
8: <title>Untitled Page</title>
9: </head>
10: <body>
11: <form id="form1" runat="server">
12: <div style="margin-left: 50px; margin-top: 50px;">
13: <table>
14: <tr>
15: <td>
16: <asp:DropDownList ID="ddlMultiColor"
17: OnSelectedIndexChanged="ddlMultiColor_OnSelectedIndexChanged"
18: runat="server" AutoPostBack="true">
19: </asp:DropDownList>
20: </td>
21: <td>
22: <div id="msgColor" runat="server">
23: </div>
24: </td>
25: </tr>
26: </table>
27: </div>
28: </form>
29: </body>
30: </html>
MultiColorDDlist.aspx.cs 程式碼，如下：
1: using System;
2: using System.Collections.Generic;
3: using System.Drawing;
4: using System.Reflection;
5: using System.Web.UI;
6:
7: public partial class MultiColorDDlist : Page
8: {
9: protected void Page_Load(object sender, EventArgs e)
10: {
11: if (!IsPostBack)
12: {
13: populateDdlMultiColor();
14: colorManipulation();
15: }
16: }
17:
18: protected void ddlMultiColor_OnSelectedIndexChanged(object sender, EventArgs e)
19: {
20: Color backColor = Color.FromName(ddlMultiColor.SelectedItem.Text);
21: ddlMultiColor.BackColor = backColor;
22: colorManipulation();
23: ddlMultiColor.Items.FindByValue(ddlMultiColor.SelectedValue).Selected = true;
24: string strStyle = string.Format("background:{0};width:30px;height:25px;",
25: ddlMultiColor.SelectedItem.Value);
26: msgColor.Attributes.Add("style", strStyle);
27: }
28:
29: private void colorManipulation()
30: {
31: for (int row = 0; row < ddlMultiColor.Items.Count - 1; row++)
32: {
33: Color backColor = Color.FromName(ddlMultiColor.Items[row].Value);
34: double grayValue = 0.299*backColor.R + 0.587*backColor.G + 0.114*backColor.B;
35: string strTextColor = (grayValue < 127.5) ? "white" : "black";
36: string strStyle = string.Format("background-color:{0}; color: {1};",
37: ddlMultiColor.Items[row].Value, strTextColor);
38:
39: ddlMultiColor.Items[row].Attributes.Add("style", strStyle);
40: }
41: ddlMultiColor.BackColor = Color.FromName(ddlMultiColor.SelectedItem.Text);
42: }
43:
44: private static List<string> finalColorList()
45: {
46: string[] allColors = Enum.GetNames(typeof (KnownColor));
47: string[] systemEnvironmentColors = new string[(typeof (SystemColors)).GetProperties().Length];
48:
49: int index = 0;
50: foreach (PropertyInfo member in (typeof (SystemColors)).GetProperties())
51: {
52: systemEnvironmentColors[index++] = member.Name;
53: }
54:
55: List<string> finalColorList = new List<string>();
56: foreach (string color in allColors)
57: {
58: if (Array.IndexOf(systemEnvironmentColors, color) < 0)
59: {
60: finalColorList.Add(color);
61: }
62: }
63:
64: return finalColorList;
65: }
66:
67: private void populateDdlMultiColor()
68: {
69: ddlMultiColor.DataSource = finalColorList();
70: ddlMultiColor.DataBind();
71: }
72: }