了解 Silverlight 调度程序 [英] Understanding the Silverlight Dispatcher
问题描述
我遇到了无效的跨线程访问问题,但经过一些研究,我设法使用 Dispatcher 修复了它.
I had a Invalid Cross Thread access issue, but a little research and I managed to fix it by using the Dispatcher.
现在在我的应用程序中,我有延迟加载的对象.我会使用 WCF 进行异步调用,并且像往常一样,我使用 Dispatcher 来更新我的对象 DataContext,但是它不适用于这种情况.但是,我确实在此处找到了解决方案.这是我不明白的地方.
Now in my app I have objects with lazy loading. I'd make an Async call using WCF and as usual I use the Dispatcher to update my objects DataContext, however it didn't work for this scenario. I did however find a solution here. Here's what I don't understand.
在我的 UserControl 中,我有代码可以在我的对象上调用 Toggle 方法.对这个方法的调用是在一个 Dispatcher 中,就像这样.
In my UserControl I have code to call an Toggle method on my object. The call to this method is within a Dispatcher like so.
Dispatcher.BeginInvoke( () => _CurrentPin.ToggleInfoPanel() );
正如我之前提到的,这不足以满足 Silverlight.我不得不在我的对象中进行另一个 Dispatcher 调用.我的对象不是 UIElement,而是一个处理自己所有加载/保存的简单类.
As I mentioned before this was not enough to satisfy Silverlight. I had to make another Dispatcher call within my object. My object is NOT a UIElement, but a simple class that handles all its own loading/saving.
所以问题是通过调用解决的
So the problem was fixed by calling
Deployment.Current.Dispatcher.BeginInvoke( () => dataContext.Detail = detail );
在我的课堂上.
为什么我必须两次调用 Dispatcher 才能实现此目的?一个高层的电话难道还不够吗?Deployment.Current.Dispatcher 和 UIElement 中的 Dispatcher 有区别吗?
Why did I have to call the Dispatcher twice to achieve this? Shouldn't a high-level call be enough? Is there a difference between the Deployment.Current.Dispatcher and the Dispatcher in a UIElement?
推荐答案
理想情况下,存储 Dispatcher
的单个实例,您可以在其他地方使用它,而无需对其进行线程检查.
Ideally, store a single instance of Dispatcher
that you can use elsewhere without having the thread check on it.
调用任何单例 .Current 实例实际上可能会导致调用跨线程访问检查.通过先存储它,您可以避免这种情况以实际获取共享实例.
Calling any singleton .Current instance may in fact cause a cross-thread access check to be invoked. By storing it first, you can avoid this to actually get the shared instance.
我使用SmartDispatcher",它在线程外调用时使用调度程序,否则仅调用.它解决了这类问题.
I use a "SmartDispatcher" that uses a dispatcher when called off-thread, and just invokes otherwise. It solves this sort of issue.
发布:http://www.jeff.wilcox.name/2010/04/propertychangedbase-crossthread/
代码:
// (c) Copyright Microsoft Corporation.
// This source is subject to the Microsoft Public License (Ms-PL).
// Please see http://go.microsoft.com/fwlink/?LinkID=131993 for details.
// All other rights reserved.
using System.ComponentModel;
namespace System.Windows.Threading
{
/// <summary>
/// A smart dispatcher system for routing actions to the user interface
/// thread.
/// </summary>
public static class SmartDispatcher
{
/// <summary>
/// A single Dispatcher instance to marshall actions to the user
/// interface thread.
/// </summary>
private static Dispatcher _instance;
/// <summary>
/// Backing field for a value indicating whether this is a design-time
/// environment.
/// </summary>
private static bool? _designer;
/// <summary>
/// Requires an instance and attempts to find a Dispatcher if one has
/// not yet been set.
/// </summary>
private static void RequireInstance()
{
if (_designer == null)
{
_designer = DesignerProperties.IsInDesignTool;
}
// Design-time is more of a no-op, won't be able to resolve the
// dispatcher if it isn't already set in these situations.
if (_designer == true)
{
return;
}
// Attempt to use the RootVisual of the plugin to retrieve a
// dispatcher instance. This call will only succeed if the current
// thread is the UI thread.
try
{
_instance = Application.Current.RootVisual.Dispatcher;
}
catch (Exception e)
{
throw new InvalidOperationException("The first time SmartDispatcher is used must be from a user interface thread. Consider having the application call Initialize, with or without an instance.", e);
}
if (_instance == null)
{
throw new InvalidOperationException("Unable to find a suitable Dispatcher instance.");
}
}
/// <summary>
/// Initializes the SmartDispatcher system, attempting to use the
/// RootVisual of the plugin to retrieve a Dispatcher instance.
/// </summary>
public static void Initialize()
{
if (_instance == null)
{
RequireInstance();
}
}
/// <summary>
/// Initializes the SmartDispatcher system with the dispatcher
/// instance.
/// </summary>
/// <param name="dispatcher">The dispatcher instance.</param>
public static void Initialize(Dispatcher dispatcher)
{
if (dispatcher == null)
{
throw new ArgumentNullException("dispatcher");
}
_instance = dispatcher;
if (_designer == null)
{
_designer = DesignerProperties.IsInDesignTool;
}
}
/// <summary>
///
/// </summary>
/// <returns></returns>
public static bool CheckAccess()
{
if (_instance == null)
{
RequireInstance();
}
return _instance.CheckAccess();
}
/// <summary>
/// Executes the specified delegate asynchronously on the user interface
/// thread. If the current thread is the user interface thread, the
/// dispatcher if not used and the operation happens immediately.
/// </summary>
/// <param name="a">A delegate to a method that takes no arguments and
/// does not return a value, which is either pushed onto the Dispatcher
/// event queue or immediately run, depending on the current thread.</param>
public static void BeginInvoke(Action a)
{
if (_instance == null)
{
RequireInstance();
}
// If the current thread is the user interface thread, skip the
// dispatcher and directly invoke the Action.
if (_instance.CheckAccess() || _designer == true)
{
a();
}
else
{
_instance.BeginInvoke(a);
}
}
}
}
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