Try & Error

using System;
using System.Windows.Forms;
using System.Threading;

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

        private void btnQuery_Click(object sender, EventArgs e)
        {
            // 작업 쓰레드 시작
            Thread worker = new Thread(Run);
            worker.Start();
        }

        private void btnClear_Click(object sender, EventArgs e)
        {
            // UI 쓰레드에서 TextBox 갱신
            UpdateTextBox(string.Empty);
        }

        private void Run()
        { 
            // Long DB query
            Thread.Sleep(3000);
            string dbData = "Query Result";

            // 작업쓰레드에서 TextBox 갱신
            UpdateTextBox(dbData);
        }

        private void UpdateTextBox(string data)
        {
            // 호출한 쓰레드가 작업쓰레드인가?
            if (textBox1.InvokeRequired)
            {
                // 작업쓰레드인 경우
                textBox1.BeginInvoke(new Action(() => textBox1.Text = data));
            }
            else 
            {
                // UI 쓰레드인 경우
                textBox1.Text = data;
            }            
        }
    }
}

using System;
using System.Windows;
using System.Threading.Tasks;

namespace WpfApp
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            // 작업쓰레드 생성
            Task.Factory.StartNew(Run);            
        }

        private void Run()
        {
            // 해당 쓰레드가 UI쓰레드인가?
            if (textBox1.Dispatcher.CheckAccess())
            {
                //UI 쓰레드인 경우
                textBox1.Text = "Data";
            }
            else
            {
                // 작업쓰레드인 경우
                textBox1.Dispatcher.BeginInvoke(new Action(Run));
            }
        }
    }
}