String[] vins = listBox1.SelectedItem.ToString().Split(" ".ToCharArray());//分离出版本和下载地址

S t r i n g v d p = A p p l i c a t i o n . S t a r t u p P a t h + " \ \ . m i n e c r a f t \ \ v e r s i o n s \ \ " + v i n s [ 0 ] ; //处理下 载 目 标 路 径，别忘了删掉空格

if (!Directory.Exists(vdp))//如果无文件夹
{
Directory.CreateDirectory(vdp);//创建
}
wc.DownloadFile(vins[1], vdp + "\\" + vins[0] + ".json");//处理并下载目标文件
while (!File.Exists(vdp + "\\" + vins[0] + ".json"))//等待下载完成
{
System.Threading.Thread.Sleep(10);//休眠
}
String rtxt = File.ReadAllText(vdp + "\\" + vins[0] + ".json").Replace(" ", "").Replace("\n", "").Replace("\r", "").Replace("\t", "");//读取数据
int a = rtxt.IndexOf("downloads");//读取主jar文件下载地址部分
int b = rtxt.IndexOf("client", a);//读取主jar文件下载地址部分
int c = rtxt.IndexOf("url", b) + "url".Length + 3;//读取主jar文件下载地址部分
List<String> cu = new List<string>();//声明下载列表
cu.Add(rtxt.Substring(c, rtxt.IndexOf("\"", c) - c) + ":::" + vdp + "\\" + vins[0] + ".jar");//加入下载项
new ShowDownload().DownloadBL(cu, "restart");//执行下载并要求重启启动器

然后我们双击“获取纯净版列表”按钮，在button4_click()中键入代码：
if (File.Exists(Application.StartupPath + "\\tmp.json"))//如果临时文件存在
{
File.Delete(Application.StartupPath + "\\tmp.json");//删掉
}
wc.DownloadFile("https://launchermeta.mojang.com/mc/game/version_manifest.json", Application.StartupPath + "\\tmp.json");//下载版本列表文件
String rtxt = File.ReadAllText(Application.StartupPath + "\\tmp.json").Replace("\n", "").Replace(" ", "");//读取版本列表
File.Delete(Application.StartupPath + "\\tmp.json");//删除临时文件
int tmp = rtxt.IndexOf("versions") + "versions".Length + 3;//读取objects数组数据
String versions_S = rtxt.Substring(tmp, rtxt.LastIndexOf("]", rtxt.Length - 1) - tmp);//同上
String[] versions = versions_S.Replace("},{", "$").Split("$".ToCharArray());//分割数组
String tmu = "";//声明并初始化tmu
listBox1.Items.Clear();//清空列表
foreach (String vi in versions)
{//为每个项循环
tmp = vi.IndexOf("id") + "id".Length + 3;//读取id
tmu = vi.Substring(tmp, vi.IndexOf("\"", tmp) - tmp);//同上
tmp = vi.IndexOf("url") + "url".Length + 3;//读取url
String tmua = vi.Substring(tmp, vi.IndexOf("\"", tmp) - tmp);//同上
listBox1.Items.Add(tmu + " " + tmua);//添加项
}

转到ShowDownload.cs，将NextDownload方法改为
private void NextDownload(object sender, AsyncCompletedEventArgs e)
{//下载任务队列执行方法
String[] uat;//声明公共数组uat
if (pointer != 0)//如果不是刚开始
{
uat = targetURL[pointer - 1].Replace(":::", "|").Split("|".ToCharArray());//处理下载地址和目标文件路径
if (new FileInfo(uat[1]).Length == 0)//检查上一个下载的文件
{//如果下载出错
File.Delete(uat[1]);//删掉有问题的文件
}
}
if (pointer == targetURL.Count)//如果下载完成
{
if (reCall == "restart")//如果要重启
{
System.Diagnostics.Process.Start(Application.ExecutablePath);//运行
Application.Exit();//退出
return;//返回
}
if (reCall != "")//如果调用不为空
{
String[] ra = reCall.Replace(",%,%,", "\"").Split("\"".ToCharArray());//处理参数
new Launcher().Launch(ra[0], ra[1], ra[2], ra[3], 0, true);//重新调用Launch方法并传参
}
this.Close();//关闭窗体
return;//退出方法执行
}
listBox1.SelectedIndex = pointer;//选中正在下载的项，以告诉用户
uat = targetURL[pointer].Replace(":::", "|").Split("|".ToCharArray());//处理下载地址和目标文件路径
String s = uat[1].Replace(Path.GetFileName(uat[1]), "");//获得文件所在文件夹路径
if (!Directory.Exists(s))//如果文件夹不存在
{
Directory.CreateDirectory(s);//创建文件夹（在C#里面可能是多余的，但是在其他编程语言中要这么做）
}
wc.DownloadFileAsync(new Uri(uat[0]), uat[1]);//下载指定的文件
pointer = pointer + 1;//指针后退
int per = pointer * 100 / targetURL.Count;//计算下载完成的百分比
progressBar1.Step = per - progressBar1.Value;//设置进度条的单次前进值
progressBar1.PerformStep();//进度条前进
progperc.Text = per + "%";//显示最新的进度百分比（已取整）
}

效果图：

当然，您也可以用bmclapi来完成。

进阶八：Forge版的下载。

您可以访问一下http://files.minecraftforge.net/，这里有所有Forge版本下载。

但是我们编写的是应用程序，它不能这么显示。

我们可以通过读取http://files.minecraftforge.net/maven/net/minecraftforge/forge/json来获取版本列表。

内容如下：
{
"adfocus": "271228",
"artifact": "forge",
"branches": {
"1.10.0": [
1981,
1982,
1983,
1984,
1986,
1989,
1991,
1992,
1993,
1994,
1995,
1996,
1997,
1999,
2000,
2001,
2002,
2003,
2004,
2005,
2006,
2007
],
"1.7.10": [
1300,
1307,
1340,
1342,
1343,
1346,
1347,
1351,
1352,
1355,
1356,
1358,
1360,
1362,
1363,
1364,
1365,
1366,
1367,
1368,
1369,
1370,
1372,
1373,
1374,
1376,
1377,
1378,
1379,
1380,
1381,
1382,
1383,
1384,
1385,
1387,
1388,
1399,
1400,
1403,
1406,
1407,
1408,
1420,
1422,
1424,
1428,
1445,
1447,
1448,
1451,
1452,
1456,
1469,
1470,
1472,
1481,
1490,
1492,
1517,
1539,
1540,
1541,
1557,
1558,
1564,
1566,
1614
],
（省略）
},
"name": "Minecraft Forge",
"number": {
（省略）
"2014": {
"branch": null,
"build": 2014,
"files": [
[
"zip",
"mdk",
"6204d951e8095c73c4148371f41c997b"
],
[
"txt",
"changelog",
"0bdda6e0cf112423fb35622c0aad4214"
],
[
"jar",
"universal",
"4126bfa051ef8d17cb858e1aae64de2a"
],
[
"jar",
"userdev",
"0b4d97e0d5605b709bdf40b4a4d88cb9"
],
[
"exe",
"installer-win",
"79b51c42661e9a505324f662bd41890f"
],
[
"jar",
"installer",
"87a2a5534b74c6f762a305a5abd2e840"
]
],
"mcversion": "1.10.2",
"modified": 1468437497.0,
"version": "12.18.1.2014"
}
},
"promos": {
"1.10-latest": 2000,
"1.10.2-latest": 2014,
"1.10.2-recommended": 2011,
"1.5.2-latest": 738,
"1.5.2-recommended": 737,
"1.6.1-latest": 775,
"1.6.2-latest": 871,
"1.6.2-recommended": 871,
"1.6.3-latest": 878,
"1.6.4-latest": 1345,
"1.6.4-recommended": 1345,
"1.7.10-latest": 1614,
"1.7.10-latest-1.7.10": 1343,
"1.7.10-recommended": 1558,
"1.7.2-latest": 1147,
"1.7.2-recommended": 1121,
"1.8-latest": 1577,
"1.8-recommended": 1563,
"1.8.8-latest": 1655,
"1.8.9-latest": 1902,
"1.8.9-recommended": 1722,
"1.9-recommended": 1887,
"1.9.4-recommended": 1976,
"latest": 2014,
"latest-1.7.10": 1343,
"recommended": 2011
},
"webpath": "http://files.minecraftforge.net/maven/net/minecraftforge/forge/"
}

"1812": {
"branch": "1.9",
"build": 1812,
"files": [
[
"zip",
"mdk",
"1a0546cd564a78135f62fc0e7265e204"
],
[
"txt",
"changelog",
"6afcf2b41dd937813a979f27b5666064"
],
[
"jar",
"universal",
"2a8490dc8e84f7e7a9846aac08c7a196"
],
[
"jar",
"userdev",
"5e4f07d8f0b56843245edfa2dbed6dbf"
],
[
"exe",
"installer-win",
"d02954efb88c7b292d04320f538637d8"
],
[
"jar",
"installer",
"344d63f0585087c1a129537328abc821"
]
],
"mcversion": "1.9",
"modified": 1459221310.0,
"version": "12.16.0.1812"
},

您看到这些内容，也许会认为只要读取纯净版的所有数字，如1.10.2的2014，然后读取"2014":{}中version的内容就行了。

这也是Forge团队希望我们做的。