c# - 线程基础

Question

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Threading;


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

        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        public void countToLots()
        {
            for (int i = 0; i < 10000000; i++)
            {
                textBox1.Text = "Counting to 10000000, value is " + i + Environment.NewLine;
            }
        }

        public void countToZero()
        {
            for (int i = 10000000; i > 0; i--)
            {
                textBox2.Text = "Counting to 0, value is " + i + Environment.NewLine;
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Thread countUp = new Thread(new ThreadStart(countToLots));
            Thread countDown = new Thread(new ThreadStart(countToZero));
            countUp.Start();
            countDown.Start();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            textBox3.Text = "Bobby bob bob " + Environment.NewLine;
        }
    }
}

我真的需要尝试掌握这个窍门——我只是不明白为什么我会收到错误消息背后的理论。有人可以帮帮我吗？

Cross-thread operation not valid: Control 'textBox1' accessed from a thread other than the thread it was created on.

Answer 1

UI 控件具有“线程亲和性”；他们不想除UI线程之外的任何东西；其中包括读写属性。对 .Text 的分配应从 UI 线程完成，方法是使用 Invoke 或 BackgroundWorker。

例如:

public void countToLots()
{
    for (int i = 0; i < 10000000; i++)
    {
        // running on bg thread
        textBox1.Invoke((MethodInvoker) delegate {
            // running on UI thread
            textBox1.Text = "Counting to 10000000, value is "
                      + i + Environment.NewLine;
        });
        // running on bg thread again
    }
}

但是注意这种线程切换是有开销的。您不应该在每次迭代时都回调 - 您应该(例如)每 [n] 次迭代更新 UI - 在上面，例如每 10000 次。