WinForm/Silverlight多线程编程中如何更新UI控件的值
单线程的winfom程序中，设置一个控件的值是很easy的事情，直接 this.TextBox1.value = "Hello World!";就搞定了，但是如果在一个新线程中这么做，比如:
{
Thread t = new Thread(new ParameterizedThreadStart(SetTextBoxValue));
//当然也可以用匿名委托写成Thread t = new Thread(SetTextBoxValue);
t.Start("Hello World");
}
void SetTextBoxValue(object obj)
{
this.textBox1.Text = obj.ToString();
}
运行时，会报出一个无情的错误：
线程间操作无效: 从不是创建控件“textBox1”的线程访问它。
究其原因，winform中的UI控件不是线程安全的，如果可以随意在任何线程中改变其值，你创建一个线程，我创建一个线程，大家都来抢着更改"TextBox1"的值，没有任何秩序的话，天下大乱...
解决办法:
1.掩耳盗铃法（Control.CheckForIllegalCrossThreadCalls = false;）--仅Winform有效
using System.Threading;
using System.Windows.Forms;
namespace ThreadTest
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
Control.CheckForIllegalCrossThreadCalls = false;//这一行是关键
}
private void btnSet_Click(object sender, EventArgs e)
{
Thread t = new Thread(new ParameterizedThreadStart(SetTextBoxValue));
t.Start("Hello World");
}
void SetTextBoxValue(object obj)
{
this.textBox1.Text = obj.ToString();
}
}
}
设置Control.CheckForIllegalCrossThreadCalls为false,相当于不检测线程之间的冲突，允许各路线程随便乱搞，当然最终TextBox1的值到底是啥难以预料，只有天知道，不过这也是最省力的办法
2.利用委托调用--最常见的办法（仅WinForm有效）
using System.Threading;
using System.Windows.Forms;
namespace ThreadTest
{
public partial class Form1 : Form
{
delegate void D(object obj);
public Form1()
{
InitializeComponent();
}
private void btnSet_Click(object sender, EventArgs e)
{
Thread t = new Thread(new ParameterizedThreadStart(SetTextBoxValue));
t.Start("Hello World");
}
void SetTextBoxValue(object obj)
{
if (textBox1.InvokeRequired)
{
D d = new D(DelegateSetValue);
textBox1.Invoke(d,obj);
}
else
{
this.textBox1.Text = obj.ToString();
}
}
void DelegateSetValue(object obj)
{
this.textBox1.Text = obj.ToString();
}
}
}
3.利用SynchronizationContext上下文 -- 最神秘的方法(Winform/Silverlight能用)
之所以说它神秘，是因为msdn官方对它的解释据说也是不清不楚
using System.Threading;
using System.Windows.Forms;
namespace ThreadTest
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void btnSet_Click(object sender, EventArgs e)
{
Thread t = new Thread(new ParameterizedThreadStart(Run));
MyPram _p = new MyPram() { context = SynchronizationContext.Current, parm = "Hello World" };
t.Start(_p);
}
void Run(object obj)
{
MyPram p = obj as MyPram;
p.context.Post(SetTextValue, p.parm);
}
void SetTextValue(object obj)
{
this.textBox1.Text = obj.ToString();
}
}
public class MyPram
{
public SynchronizationContext context { set; get; }
public object parm { set; get; }
}
}
4.利用BackgroundWorker --最偷懒的办法(Winform/Silverlight通用)
BackgroundWorker会在主线程之外，另开一个后台线程，我们可以把一些处理放在后台线程中处理，完成之后，后台线程会把结果传递给主线程，同时结束自己。
using System.ComponentModel;
using System.Windows.Forms;
namespace ThreadTest
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void btnSet_Click(object sender, EventArgs e)
{
//MessageBox.Show(Thread.CurrentThread.ManagedThreadId.ToString());
using (BackgroundWorker bw = new BackgroundWorker())
{
bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
bw.DoWork += new DoWorkEventHandler(bw_DoWork);
bw.RunWorkerAsync("Hello World");
}
}
void bw_DoWork(object sender, DoWorkEventArgs e)
{
//MessageBox.Show(Thread.CurrentThread.ManagedThreadId.ToString());
e.Result = e.Argument;//这里只是简单的把参数当做结果返回，当然您也可以在这里做复杂的处理后，再返回自己想要的结果(这里的操作是在另一个线程上完成的)
}
void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
//这时后台线程已经完成，并返回了主线程，所以可以直接使用UI控件了
this.textBox1.Text = e.Result.ToString();
//MessageBox.Show(Thread.CurrentThread.ManagedThreadId.ToString());
}
}
}
5.Dispatcher.BeginInvoke--Silverlight的独门秘籍
代码
using System.Threading;
using System.Windows.Controls;
using System.Windows.Input;
namespace ThreadTest
{
public partial class MainPage : UserControl
{
public MainPage()
{
InitializeComponent();
}
private void LayoutRoot_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
Thread t = new Thread(SetTextValue);
t.Start("Hello World");
}
void SetTextValue(object text)
{
this.Dispatcher.BeginInvoke(() => { this.txt.Text = text.ToString(); });
}
}
}
using System.Windows.Controls;
using System.Windows.Input;
namespace ThreadTest
{
public partial class MainPage : UserControl
{
public MainPage()
{
InitializeComponent();
}
private void LayoutRoot_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
Thread t = new Thread(SetTextValue);
t.Start("Hello World");
}
void SetTextValue(object text)
{
this.Dispatcher.BeginInvoke(() => { this.txt.Text = text.ToString(); });
}
}
}