~楓花雪岳~: [C#] 環境變數

星期五, 4月 12, 2024

[C#] 環境變數

要透過 C# 存取 Windows 環境變數，要了解下述函式

EnvironmentVariableTarget

環境變數範圍

Process：目前 Process
User：儲存在 HKEY_CURRENT_USER\Environment
Machine：儲存在 HKEY_CURRENT_USER\Environment

把環境變數存放在 Process 的話，該 Process 結束後環境變數也就消失囉

Environment.SetEnvironmentVariable

新增或修改

環境變數不存在：新增
環境變數存在：修改

刪除，值設定為下列三者都算是要刪除該環境變數

null (該範例使用)
String.Empty
U+0000

刪除時假如該環境變數不存在，不會拋錯誤

簡易範例

WinForms 簡易範例來對環境變數進行 CRUD

using System.Collections;

namespace EnvVarSample
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            dgvSearch.AutoGenerateColumns = false;
            cboSearch.DataSource = Enum.GetNames(typeof(EnvironmentVariableTarget));
            cboEnvironmentVariableTarget.DataSource = Enum.GetNames(typeof(EnvironmentVariableTarget));
        }

        private void cboSearch_SelectionChangeCommitted(object sender, EventArgs e)
        {
            var (_, _, target) = GetValue();

            var source = new List<Source>();
            IDictionary vars = Environment.GetEnvironmentVariables(target);
            foreach (DictionaryEntry entry in vars)
                source.Add(new Source() { EnvVar = entry.Key.ToString(), Value = entry.Value.ToString() });

            dgvSearch.DataSource = source;
        }

        private void btnAddOrModify_Click(object sender, EventArgs e)
        {
            var input = GetValue();
            Environment.SetEnvironmentVariable(input.EnvVar, input.Value, input.Target);
        }

        private void btnDelete_Click(object sender, EventArgs e)
        {
            var (EvnVar, _, target) = GetValue();
            Environment.SetEnvironmentVariable(EvnVar, null, target);
        }

        private (string EnvVar, string Value, EnvironmentVariableTarget Target) GetValue()
        {
            string item = cboEnvironmentVariableTarget.SelectedItem.ToString();
            if (Enum.TryParse(item, out EnvironmentVariableTarget target) == false)
                throw new NotSupportedException(nameof(item));

            return (
                txtEnvVar.Text.Trim(),
                txtValue.Text.Trim(),
                target);
        }

        private void dgvSearch_SelectionChanged(object sender, EventArgs e)
        {
            if (dgvSearch.CurrentRow == null)
                return;

            cboEnvironmentVariableTarget.SelectedIndex = cboEnvironmentVariableTarget.FindStringExact(cboSearch.SelectedItem.ToString());
            txtEnvVar.Text = dgvSearch.CurrentRow.Cells[ColEnvVar.Index].Value?.ToString();
            txtValue.Text = dgvSearch.CurrentRow.Cells[ColValue.Index].Value?.ToString();
        }

        private class Source
        {
            public string EnvVar { get; set; }

            public string Value { get; set; }
        }

    }
}

GetEnvironmentVariables() 和 SetEnvironmentVariable() 沒有指定 EnvironmentVariableTarget 的多載，其 EnvironmentVariableTarget 為 Process 喔