背景： 很多小伙伴经常在群里问线程的问题，平时我经常转一些视频教程这些人不看，我就自己写个总结吧
不过还是要注意的是，切换本来就不能太频繁，要一口气改。
UI线程切换的核心思路是
1，这行代码会直接修改UI的，必须放在UI线程，掌握这条你可以自己把winform的线程检查关掉，将Control类的静态属性CheckForIllegalCrossThreadCalls设为false，必须心里有数才能做此操作
2，wpf也是如此，但是无法关闭线程检查，但是wpf的viewmodel就不需要UI线程，更新更方便，因为是内部通知的。
一，开启一个新的任务
var param = ; //net4.5以后
Task.Run(() =>
{
DoSomthing(param);
}); Task.Run(async () =>
{
await DoSomthingAsync(param);
}); //net 4.0 Task.Factory.StartNew(delegate ()
{
DoSomthing(param);
}); //3.5
Thread t = new Thread((ThreadStart)delegate ()
{
DoSomthing(param);
});
t.Start();
//net 3.5 加线程池
ThreadPool.QueueUserWorkItem((WaitCallback)delegate (Object obj)
{
DoSomthing(param);
});
后面都用Task为例
二， 回到UI线程
//winform
Task.Run(() =>
{
//类似sendMessage 等待发送结束
this.Invoke((Action)delegate ()
{
DoSomthing(param);
});
//类似postmessage 发了就跑
this.BeginInvoke((Action)delegate ()
{
DoSomthing(param);
});
}); //wpf
Task.Run(async () =>
{
this.Dispatcher.Invoke(delegate ()
{
DoSomthing(param);
}); //使用异步等待任务结束
await this.Dispatcher.BeginInvoke((Action)delegate ()
{
DoSomthing(param);
});
//使用抛弃返回值的方式，直接过 不等待
_ = this.Dispatcher.BeginInvoke((Action)delegate ()
{
DoSomthing(param);
});
});
await Task.Run(async () =>
{
DoSomething();
}
//回到调用线程
三， 高级方法
1 使用 SynchronizationContext
//在UI线程时记录下上下文
var syncContext = SynchronizationContext.Current;
Task.Run(() =>
{
//使用UI线程
syncContext.Post(o =>
{
DoSomthing(param);
}, null);
});
2 await一个SynchronizationContext
//在UI线程时记录下上下文
var syncContext = SynchronizationContext.Current;
Task.Run(() =>
{
//回到UI线程
await syncContext;
DoSomthing(param);//在UI线程中
});
那么如何await一个SynchronizationContext呢？
//写个Awaiter类
public sealed class SynchronizationContextAwaiter : INotifyCompletion
{
private readonly SynchronizationContext _context;
public SynchronizationContextAwaiter(SynchronizationContext context) =>
_context = context ?? throw new ArgumentNullException("context"); public bool IsCompleted => SynchronizationContext.Current == _context;
public void OnCompleted(Action action) => _context.Post(x => action(), null);
public void GetResult() { }
} //接下去使用awaiter类，写个扩展方法
public static SynchronizationContextAwaiter GetAwaiter(this SynchronizationContext context)
{
return new SynchronizationContextAwaiter(context);
}
四，将三的内容整合到一个类中
需要在UI线程初始化：
UIThreadContext.Init();
using Ruifei.Common.UIThread;
using System;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Threading; public static class UIThreadContext
{
public static SynchronizationContext Context;
public static Thread UIThread => uiThread;
static Thread uiThread = null;
public static void SendUIThread(Action action)
{
if (Context != null)
Context.Send(x => action(), null);
else
action();
} public static void SendUIThreadIfRequired(Action action)
{
Thread crt = Thread.CurrentThread;
if (uiThread != crt)
SendUIThread(action);
else
action();
} public static void PostUIThread(Action action)
{
if (Context != null)
Context.Post(x => action(), null);
else
action();
} public static void PostUIThread(Func<Task> action)
{
if (Context != null)
Context.Post(x => action(), null);
else
action();
} public static void PostUIThreadIfRequired(Action action)
{
if (IsInUIThread())
action();
else
PostUIThread(action);
} public static void PostUIThreadIfRequired(Func<Task> action)
{
if (IsInUIThread())
action();
else
PostUIThread(action);
} public static bool IsInUIThread()
{
return uiThread == Thread.CurrentThread;
} static Dispatcher dispatcher = (Application.Current != null && Application.Current.Dispatcher != null) ? Application.Current.Dispatcher : Dispatcher.CurrentDispatcher;
public async static void InvokeOnUIThread(Func<Task> action)
{
if (dispatcher == null || dispatcher.CheckAccess())
await action();
else
await dispatcher.BeginInvoke(action);
} public static void InvokeOnUIThread(Action action)
{
if (dispatcher == null || dispatcher.CheckAccess())
action();
else
dispatcher.BeginInvoke(action);
} public static void Init()
{
Context = SynchronizationContext.Current;
uiThread = Thread.CurrentThread;
} public static SynchronizationContextAwaiter GetAwaiter(this SynchronizationContext context)
{
return new SynchronizationContextAwaiter(context);
} /// <summary>
/// 切换到UI线程
/// </summary>
/// <returns></returns>
public static SynchronizationContext SwitchToUIThread()
{
return UIThreadContext.Context;
} /// <summary>
/// WithoutContext
/// </summary>
/// <returns></returns>
public static WaitForSwitchToNewTask SwitchToNewTask()
{
return new WaitForSwitchToNewTask(false);
}
} namespace Ruifei.Common.UIThread
{
public class WaitForSwitchToNewTask
{
bool withContext = false;
public WaitForSwitchToNewTask(bool _with)
{
withContext = _with;
}
public ConfiguredTaskAwaitable.ConfiguredTaskAwaiter GetAwaiter()
{
return Task.Run(() => { }).ConfigureAwait(withContext).GetAwaiter();
}
} public sealed class SynchronizationContextAwaiter : INotifyCompletion
{
private readonly SynchronizationContext _context;
public SynchronizationContextAwaiter(SynchronizationContext context) =>
_context = context ?? throw new ArgumentNullException("context"); public bool IsCompleted => SynchronizationContext.Current == _context;
public void OnCompleted(Action action)
{
if (_context == null)
{
action();
}
else
{
_context.Send(x => action(), null);
}
} public void GetResult() { }
}
}
