从另一个线程获取控件的属性

Question

我想从窗体中的BackgroundWorker获取控件的属性：

foreach (ListViewItem i in ListView.CheckedItems) { //error: Cross-thread operation not valid: Control 'ListView' accessed from a thread other than the thread it was created on.
    //do something with i
}

有谁能建议最简单和最容易的方法来做这件事吗？

Answer 1

让我再试一次...

1.)将ListView拖到窗体上

2.)将BackgroundWorker拖到窗体上

3.)创建一个遍历ListViewItem集合的方法

private void LoopThroughListItems()
{
    foreach (ListViewItem i in listView1.CheckedItems)
        DoSomething(); 

}

4.)添加代码以在BackgroundWorker的DoWork事件内调用LoopThroughListItems()

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
    LoopThroughListItems();
}

5.)在表单中，加载-在主线程上执行代码(可以工作)，然后在backgroundWorkder线程上执行代码(失败)

private void Form1_Load(object sender, EventArgs e)
{
    // Try it on the UI Thread - It works
    LoopThroughListItems();

    // Try it on a Background Thread - It fails
    backgroundWorker1.RunWorkerAsync();

}

6.)修改代码以使用IsInvokeRequired/Invoke

private void LoopThroughListItems()
{

    // InvokeRequired == True when executed by non-UI thread
    if (listView1.InvokeRequired)
    {
        // This will re-call LoopThroughListItems - on the UI Thread
        listView1.Invoke(new Action(LoopThroughListItems));
        return;
    }

    foreach (ListViewItem i in listView1.CheckedItems)
        DoSomething(); 
}

7.)再次运行应用程序-现在它可以在UI线程和非UI线程上运行。

这就解决了问题。检查IsInvokeRequired/Invoking是一种常见的模式，您会经常使用它(这就是为什么它包含在所有控件中)。如果你到处都在做这件事，你可以做一些聪明的事情，然后把它都包装起来--就像这里描述的那样：Automating the InvokeRequired code pattern

Answer 2

尝试如下所示：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void OnClick(object sender, EventArgs e)
        {
            backgroundWorker1.RunWorkerAsync();
        }

        private void OnDoWork(object sender, DoWorkEventArgs e)
        {
            foreach (ListViewItem i in GetItems(listView1))
            {
                DoSomething(i);
            }
        }

        private IEnumerable<ListViewItem> GetItems(ListView listView)
        {
            if (InvokeRequired)
            {
                var func = new Func<ListView, IEnumerable<ListViewItem>>(GetItems);
                return (IEnumerable<ListViewItem>)Invoke(func, new[] { listView });
            }
            // Create a defensive copy to avoid iterating outsite UI thread
            return listView.CheckedItems.OfType<ListViewItem>().ToList();
        }

        private void DoSomething(ListViewItem item)
        {
            if (InvokeRequired)
            {
                var action = new Action<ListViewItem>(DoSomething);
                Invoke(action, new[] { item });
                return;
            }
            // Do whatever you want with i
            item.Checked = false;
        }
    }
}

然而，你的问题真的很笼统。如果你分享更多的细节，也许会有一个更容易或更好的解决方案。