通过嵌套方法使用 TPL 时无法更新 UI 个元素
Unable to update UI elements when using TPL through nested methods
我正在尝试使用 TPL 从多种方法更新 UI 元素。当执行第一个方法时，元素会更新，但是当调用嵌套在第一个方法中的子方法时，我得到一个 InvalidOperationException-当前的 SynchronizationContext 不能用作 TaskScheduler。我什至尝试将代码转换为 async - await 模式但没有成功。
编辑 1：无法重现 InvalidOperationException。我现在收到此错误 - 当前的 SynchronizationContext 不能用作 TaskScheduler。
编辑 2：重现了 InvalidOperationException。这是由于当前的 SynchronizationContext 可能未用作 TaskScheduler 引起的。堆栈跟踪如下：
at
System.Threading.Tasks.SynchronizationContextTaskScheduler..ctor()
at
System.Threading.Tasks.TaskScheduler.FromCurrentSynchronizationContext()
at IntegratedTracker.IntegratedTracker.ProgressReporter..ctor() in
at IntegratedTracker.IntegratedTracker.UploadToDb() in
at System.Threading.Tasks.Task.InnerInvoke() at
System.Threading.Tasks.Task.Execute()
此外，我注意到如果我在 button_click 事件中调用 UpdateValuesInDb 方法，更新会流向 UI。
我的代码连同我所做的研究一起在下面提交，这些研究在代码的注释中。
private void btnUploadToDb_Click(object sender, EventArgs e)
{
UploadToDb();
}
private static void UploadToDb()
{
Task.Factory.StartNew(()=>
{
for (int i = 0; i <= maxRecords - 1; i++)
{
// Code for inserting into Db.
// Update progress to progressbar and label on UI form.
// Borrowed from Stephen Cleary's article
// http://blog.stephencleary.com/2010/06/reporting-progress-from-tasks.html
progressReporter.ReportProgress(() => {
// Can this be done in a better way than enclosing in a
// ReportProgress before entering the for loop?
progressbar.maximum=maxRecords;
label.text="Uploading " + i;
progressbar.value=i;
});
}
progressReporter.ReportProgress(() => {
label.Text = "Updating values in DB, please wait...";
});
// When this call is made the subsequent updates to the main form
// were not successful due to 'InvalidOperationException'.
UpdateValuesInDb();
});
}
private void UpdateValuesInDb();
{
// Code for updating the values.
// The below method should be called in sequence and labels updated in the same sequence.
// Report progress to UI for values of type 1.
// label.text="Moving values of type 1..."; // This has not been implemented because of cross thread exceptions
// This is what I'd like to achieve.
MoveValuesToNewDbDeleteFromSourceDb(values); // This call has to complete first
// Report progress to UI for values of type 2.
// label.text="Moving values of type 2..."; // This has not been implemented because of cross thread exceptions
// This is what I'd like to achieve.
MoveValuesToNewDbDeleteFromSourceDb(values); // This call has to complete second.
// Report progress to UI for values of type 3.
label.text="Moving values of type 3..."; // This has not been implemented because of cross thread exceptions
// This is what I'd like to achieve.
MoveValuesToNewDbDeleteFromSourceDb(values); // This call has to complete third.
// Report progress to UI for values of type 4.
// label.text="Moving values of type 4..."; // This has not been implemented because of cross thread exceptions
// This is what I'd like to achieve.
MoveValuesToNewDbDeleteFromSourceDb(values); // This call is the final.
}
private void MoveValuesToNewDbDeleteFromSourceDb(string values)
{
var progressReporter = new ProgressReporter();
Task.Factory.StartNew(() => {
for (int i = 0; i <= dt.Rows.Count - 1; i++)
{
// Tried using Stephen Cleary's code here but it fails with
progressReporter.ReportProgress(() =>
{
progressBar.Maximum = maxRecords - 1;
Label.Text = "Uploading " + i;
progressBar.Value = i;
});
// Need to update label and progress in for loop as mentioned above.
}
});
}
我什至尝试将现有代码转换为使用 async-await 方法，但它在编译期间失败，表明它不可等待。
这是我尝试更改的内容：
private async void btnUploadToDb_Click(object sender, EventArgs e)
{
await UploadToDb(); // Got the error Type System.Threading.Tasks.Task is not awaitable.
}
private async Task UploadToDb()
{
// Codes is same as the previous one, I've just used the async
// modifier, though I do not know what to await here.
// Tried to assign await as follows:
await Task.Factory.StartNew(() => {
for (int i = 0; i <= dt.Rows.Count - 1; i++)
{
// Need to update label and progress bar here.
}
});
// The above results in a compile error:
// 'Type System.Threading.Tasks.Task is not awaitable'.
}
我什至搜索了有关 TPL、初学者 TPL 等的教程，但是 none 这对解决我的问题很有帮助。
此外，我想知道我们是否需要处理创建的任务，或者这些任务是否像 using 块一样自动处理。如果在任务完成前遇到异常，是否需要处理任务？
我是 TPL 的新手，我正在为这些概念苦苦挣扎，因此非常感谢您的帮助。
忘了说，我正在使用 VS2010、.Net 4.0，这是用于 Windows Forms 应用程序。
您不想在 MoveValuesToNewDbDeleteFromSourceDb 方法中开始新任务，因为：
The below method should be called in sequence and labels updated in the same sequence.
为什么不将该方法更改为如下所示：
private void MoveValuesToNewDbDeleteFromSourceDb(string valuesType, string values)
{
progressReporter.ReportProgress(() => {
label.text = string.Format("Moving values of type {0}...", valuesType);
});
for (int i = 0; i <= dt.Rows.Count - 1; i++)
{
// Do your move values thing.
// Report progress
progressReporter.ReportProgress(() => {
// ...
});
}
}
并这样称呼它：
private void UpdateValuesInDb();
{
// Code for updating the values.
// The below method should be called in sequence
// and labels updated in the same sequence.
// for type "1" .. "4".
MoveValuesToNewDbDeleteFromSourceDb("1", values);
MoveValuesToNewDbDeleteFromSourceDb("2", values);
MoveValuesToNewDbDeleteFromSourceDb("3", values);
MoveValuesToNewDbDeleteFromSourceDb("4", values);
}
注：如博文所述，ProgressReporter为"deprecated":
Update, 2012-02-16: The information in this post is old. See the new post Reporting Progress from Async Tasks for a better solution.
第二个注意事项：我假设您的 progressReporter 实例是一个成员变量，它是在您的 UI 线程 上创建的 。如果不是这种情况，这就解释了您遇到问题的原因：将其设为成员变量，在创建表单时构造它。
最后，您可以使用更简单的实现来满足您的需求。
public class ProgressReporter
{
private readonly SynchronizationContext _syncContext = SynchronizationContext.Current;
public void ReportProgress(Action progressAction)
{
_syncContext.Post(new SendOrPostCallback(unused => progressAction()), null);
}
}
如果您的应用程序 运行 在 STAThreadApartment 中，那么它可能会发生。
尝试使用 ConfigureAwait(false) 调用您的任务以防止使用默认的 SyncThreadContext。
虽然它可能会改变异步的行为。但如果我的假设是正确的，这可能会解决问题。
Update: You're on .Net 4.0 so ConfigureAwait is out of context.
问题可能是当您从嵌套方法创建任务时，您的 Synchrnoization 上下文可能会设置回 null。您可以从父方法获取当前同步上下文，并为所有嵌套方法使用相同的上下文。
我已经更新了你的代码：
private static void UploadToDb()
{
var currentSyncContext = TaskScheduler.FromCurrentSynchronizationContext();
Task.Factory.StartNew(()=>
{
for (int i = 0; i <= maxRecords - 1; i++)
{
progressReporter.ReportProgress(() => {
progressbar.maximum=maxRecords;
label.text="Uploading " + i;
progressbar.value=i;
});
}
progressReporter.ReportProgress(() => {
label.Text = "Updating values in DB, please wait...";
});
// When this call is made the subsequent updates to the main form
// were not successful due to 'InvalidOperationException'.
UpdateValuesInDb(currentSyncContext);
});
}
private void UpdateValuesInDb(SynchronizationContext context);
{
MoveValuesToNewDbDeleteFromSourceDb(values, context);
MoveValuesToNewDbDeleteFromSourceDb(values, context);
label.text="Moving values of type 3...";
MoveValuesToNewDbDeleteFromSourceDb(values, context);
MoveValuesToNewDbDeleteFromSourceDb(values, context); // This call is the final.
}
private void MoveValuesToNewDbDeleteFromSourceDb(string values, SynchronizationContext context)
{
var progressReporter = new ProgressReporter();
Task.Factory.StartNew(() => {
for (int i = 0; i <= dt.Rows.Count - 1; i++)
{
// Tried using Stephen Cleary's code here but it fails with
progressReporter.ReportProgress(() =>
{
progressBar.Maximum = maxRecords - 1;
Label.Text = "Uploading " + i;
progressBar.Value = i;
});
// Need to update label and progress in for loop as mentioned above.
}
}, context);
}
ProgressReporter 必须在 UI 线程上创建。因此，您需要将行 var progressReporter = new ProgressReporter(); 从 MoveValuesToNewDbDeleteFromSourceDb 的顶部移动到 UploadToDb 的顶部。
并且强烈考虑升级您的Visual Studio版本。使用 async/await 和 IProgress<T> 而不是 ProgressReporter.
要容易得多
我正在尝试使用 TPL 从多种方法更新 UI 元素。当执行第一个方法时，元素会更新，但是当调用嵌套在第一个方法中的子方法时，我得到一个 InvalidOperationException-当前的 SynchronizationContext 不能用作 TaskScheduler。我什至尝试将代码转换为 async - await 模式但没有成功。
编辑 1：无法重现 InvalidOperationException。我现在收到此错误 - 当前的 SynchronizationContext 不能用作 TaskScheduler。
编辑 2：重现了 InvalidOperationException。这是由于当前的 SynchronizationContext 可能未用作 TaskScheduler 引起的。堆栈跟踪如下：
at System.Threading.Tasks.SynchronizationContextTaskScheduler..ctor()
at System.Threading.Tasks.TaskScheduler.FromCurrentSynchronizationContext() at IntegratedTracker.IntegratedTracker.ProgressReporter..ctor() in
at IntegratedTracker.IntegratedTracker.UploadToDb() in
at System.Threading.Tasks.Task.InnerInvoke() at System.Threading.Tasks.Task.Execute()
此外，我注意到如果我在 button_click 事件中调用 UpdateValuesInDb 方法，更新会流向 UI。
我的代码连同我所做的研究一起在下面提交，这些研究在代码的注释中。
private void btnUploadToDb_Click(object sender, EventArgs e)
{
UploadToDb();
}
private static void UploadToDb()
{
Task.Factory.StartNew(()=>
{
for (int i = 0; i <= maxRecords - 1; i++)
{
// Code for inserting into Db.
// Update progress to progressbar and label on UI form.
// Borrowed from Stephen Cleary's article
// http://blog.stephencleary.com/2010/06/reporting-progress-from-tasks.html
progressReporter.ReportProgress(() => {
// Can this be done in a better way than enclosing in a
// ReportProgress before entering the for loop?
progressbar.maximum=maxRecords;
label.text="Uploading " + i;
progressbar.value=i;
});
}
progressReporter.ReportProgress(() => {
label.Text = "Updating values in DB, please wait...";
});
// When this call is made the subsequent updates to the main form
// were not successful due to 'InvalidOperationException'.
UpdateValuesInDb();
});
}
private void UpdateValuesInDb();
{
// Code for updating the values.
// The below method should be called in sequence and labels updated in the same sequence.
// Report progress to UI for values of type 1.
// label.text="Moving values of type 1..."; // This has not been implemented because of cross thread exceptions
// This is what I'd like to achieve.
MoveValuesToNewDbDeleteFromSourceDb(values); // This call has to complete first
// Report progress to UI for values of type 2.
// label.text="Moving values of type 2..."; // This has not been implemented because of cross thread exceptions
// This is what I'd like to achieve.
MoveValuesToNewDbDeleteFromSourceDb(values); // This call has to complete second.
// Report progress to UI for values of type 3.
label.text="Moving values of type 3..."; // This has not been implemented because of cross thread exceptions
// This is what I'd like to achieve.
MoveValuesToNewDbDeleteFromSourceDb(values); // This call has to complete third.
// Report progress to UI for values of type 4.
// label.text="Moving values of type 4..."; // This has not been implemented because of cross thread exceptions
// This is what I'd like to achieve.
MoveValuesToNewDbDeleteFromSourceDb(values); // This call is the final.
}
private void MoveValuesToNewDbDeleteFromSourceDb(string values)
{
var progressReporter = new ProgressReporter();
Task.Factory.StartNew(() => {
for (int i = 0; i <= dt.Rows.Count - 1; i++)
{
// Tried using Stephen Cleary's code here but it fails with
progressReporter.ReportProgress(() =>
{
progressBar.Maximum = maxRecords - 1;
Label.Text = "Uploading " + i;
progressBar.Value = i;
});
// Need to update label and progress in for loop as mentioned above.
}
});
}
我什至尝试将现有代码转换为使用 async-await 方法，但它在编译期间失败，表明它不可等待。 这是我尝试更改的内容：
private async void btnUploadToDb_Click(object sender, EventArgs e)
{
await UploadToDb(); // Got the error Type System.Threading.Tasks.Task is not awaitable.
}
private async Task UploadToDb()
{
// Codes is same as the previous one, I've just used the async
// modifier, though I do not know what to await here.
// Tried to assign await as follows:
await Task.Factory.StartNew(() => {
for (int i = 0; i <= dt.Rows.Count - 1; i++)
{
// Need to update label and progress bar here.
}
});
// The above results in a compile error:
// 'Type System.Threading.Tasks.Task is not awaitable'.
}
我什至搜索了有关 TPL、初学者 TPL 等的教程，但是 none 这对解决我的问题很有帮助。
此外，我想知道我们是否需要处理创建的任务，或者这些任务是否像 using 块一样自动处理。如果在任务完成前遇到异常，是否需要处理任务？
我是 TPL 的新手，我正在为这些概念苦苦挣扎，因此非常感谢您的帮助。
忘了说，我正在使用 VS2010、.Net 4.0，这是用于 Windows Forms 应用程序。
您不想在 MoveValuesToNewDbDeleteFromSourceDb 方法中开始新任务，因为：
The below method should be called in sequence and labels updated in the same sequence.
为什么不将该方法更改为如下所示：
private void MoveValuesToNewDbDeleteFromSourceDb(string valuesType, string values)
{
progressReporter.ReportProgress(() => {
label.text = string.Format("Moving values of type {0}...", valuesType);
});
for (int i = 0; i <= dt.Rows.Count - 1; i++)
{
// Do your move values thing.
// Report progress
progressReporter.ReportProgress(() => {
// ...
});
}
}
并这样称呼它：
private void UpdateValuesInDb();
{
// Code for updating the values.
// The below method should be called in sequence
// and labels updated in the same sequence.
// for type "1" .. "4".
MoveValuesToNewDbDeleteFromSourceDb("1", values);
MoveValuesToNewDbDeleteFromSourceDb("2", values);
MoveValuesToNewDbDeleteFromSourceDb("3", values);
MoveValuesToNewDbDeleteFromSourceDb("4", values);
}
注：如博文所述，ProgressReporter为"deprecated":
Update, 2012-02-16: The information in this post is old. See the new post Reporting Progress from Async Tasks for a better solution.
第二个注意事项：我假设您的 progressReporter 实例是一个成员变量，它是在您的 UI 线程 上创建的 。如果不是这种情况，这就解释了您遇到问题的原因：将其设为成员变量，在创建表单时构造它。
最后，您可以使用更简单的实现来满足您的需求。
public class ProgressReporter
{
private readonly SynchronizationContext _syncContext = SynchronizationContext.Current;
public void ReportProgress(Action progressAction)
{
_syncContext.Post(new SendOrPostCallback(unused => progressAction()), null);
}
}
如果您的应用程序 运行 在 STAThreadApartment 中，那么它可能会发生。
尝试使用 ConfigureAwait(false) 调用您的任务以防止使用默认的 SyncThreadContext。
虽然它可能会改变异步的行为。但如果我的假设是正确的，这可能会解决问题。
Update: You're on .Net 4.0 so ConfigureAwait is out of context.
问题可能是当您从嵌套方法创建任务时，您的 Synchrnoization 上下文可能会设置回 null。您可以从父方法获取当前同步上下文，并为所有嵌套方法使用相同的上下文。
我已经更新了你的代码：
private static void UploadToDb()
{
var currentSyncContext = TaskScheduler.FromCurrentSynchronizationContext();
Task.Factory.StartNew(()=>
{
for (int i = 0; i <= maxRecords - 1; i++)
{
progressReporter.ReportProgress(() => {
progressbar.maximum=maxRecords;
label.text="Uploading " + i;
progressbar.value=i;
});
}
progressReporter.ReportProgress(() => {
label.Text = "Updating values in DB, please wait...";
});
// When this call is made the subsequent updates to the main form
// were not successful due to 'InvalidOperationException'.
UpdateValuesInDb(currentSyncContext);
});
}
private void UpdateValuesInDb(SynchronizationContext context);
{
MoveValuesToNewDbDeleteFromSourceDb(values, context);
MoveValuesToNewDbDeleteFromSourceDb(values, context);
label.text="Moving values of type 3...";
MoveValuesToNewDbDeleteFromSourceDb(values, context);
MoveValuesToNewDbDeleteFromSourceDb(values, context); // This call is the final.
}
private void MoveValuesToNewDbDeleteFromSourceDb(string values, SynchronizationContext context)
{
var progressReporter = new ProgressReporter();
Task.Factory.StartNew(() => {
for (int i = 0; i <= dt.Rows.Count - 1; i++)
{
// Tried using Stephen Cleary's code here but it fails with
progressReporter.ReportProgress(() =>
{
progressBar.Maximum = maxRecords - 1;
Label.Text = "Uploading " + i;
progressBar.Value = i;
});
// Need to update label and progress in for loop as mentioned above.
}
}, context);
}
ProgressReporter 必须在 UI 线程上创建。因此，您需要将行 var progressReporter = new ProgressReporter(); 从 MoveValuesToNewDbDeleteFromSourceDb 的顶部移动到 UploadToDb 的顶部。
并且强烈考虑升级您的Visual Studio版本。使用 async/await 和 IProgress<T> 而不是 ProgressReporter.