问题
My code is as below
public CountryStandards()
{
InitializeComponent();
try
{
FillPageControls();
}
catch (Exception ex)
{
MessageBox.Show(ex.Message, \"Country Standards\", MessageBoxButton.OK, MessageBoxImage.Error);
}
}
/// <summary>
/// Fills the page controls.
/// </summary>
private void FillPageControls()
{
popUpProgressBar.IsOpen = true;
lblProgress.Content = \"Loading. Please wait...\";
progress.IsIndeterminate = true;
worker = new BackgroundWorker();
worker.DoWork += new System.ComponentModel.DoWorkEventHandler(worker_DoWork);
worker.ProgressChanged += new System.ComponentModel.ProgressChangedEventHandler(worker_ProgressChanged);
worker.WorkerReportsProgress = true;
worker.WorkerSupportsCancellation = true;
worker.RunWorkerCompleted += new System.ComponentModel.RunWorkerCompletedEventHandler(worker_RunWorkerCompleted);
worker.RunWorkerAsync();
}
private void worker_DoWork(object sender, System.ComponentModel.DoWorkEventArgs e)
{
GetGridData(null, 0); // filling grid
}
private void worker_ProgressChanged(object sender, System.ComponentModel.ProgressChangedEventArgs e)
{
progress.Value = e.ProgressPercentage;
}
private void worker_RunWorkerCompleted(object sender, System.ComponentModel.RunWorkerCompletedEventArgs e)
{
worker = null;
popUpProgressBar.IsOpen = false;
//filling Region dropdown
Standards.UDMCountryStandards objUDMCountryStandards = new Standards.UDMCountryStandards();
objUDMCountryStandards.Operation = \"SELECT_REGION\";
DataSet dsRegionStandards = objStandardsBusinessLayer.GetCountryStandards(objUDMCountryStandards);
if (!StandardsDefault.IsNullOrEmptyDataTable(dsRegionStandards, 0))
StandardsDefault.FillComboBox(cmbRegion, dsRegionStandards.Tables[0], \"Region\", \"RegionId\");
//filling Currency dropdown
objUDMCountryStandards = new Standards.UDMCountryStandards();
objUDMCountryStandards.Operation = \"SELECT_CURRENCY\";
DataSet dsCurrencyStandards = objStandardsBusinessLayer.GetCountryStandards(objUDMCountryStandards);
if (!StandardsDefault.IsNullOrEmptyDataTable(dsCurrencyStandards, 0))
StandardsDefault.FillComboBox(cmbCurrency, dsCurrencyStandards.Tables[0], \"CurrencyName\", \"CurrencyId\");
if (Users.UserRole != \"Admin\")
btnSave.IsEnabled = false;
}
/// <summary>
/// Gets the grid data.
/// </summary>
/// <param name=\"sender\">The sender.</param>
/// <param name=\"pageIndex\">Index of the page.( used in case of paging) </pamam>
private void GetGridData(object sender, int pageIndex)
{
Standards.UDMCountryStandards objUDMCountryStandards = new Standards.UDMCountryStandards();
objUDMCountryStandards.Operation = \"SELECT\";
objUDMCountryStandards.Country = txtSearchCountry.Text.Trim() != string.Empty ? txtSearchCountry.Text : null;
DataSet dsCountryStandards = objStandardsBusinessLayer.GetCountryStandards(objUDMCountryStandards);
if (!StandardsDefault.IsNullOrEmptyDataTable(dsCountryStandards, 0) && (chkbxMarketsSearch.IsChecked == true || chkbxBudgetsSearch.IsChecked == true || chkbxProgramsSearch.IsChecked == true))
{
DataTable objDataTable = StandardsDefault.FilterDatatableForModules(dsCountryStandards.Tables[0], \"Country\", chkbxMarketsSearch, chkbxBudgetsSearch, chkbxProgramsSearch);
dgCountryList.ItemsSource = objDataTable.DefaultView;
}
else
{
MessageBox.Show(\"No Records Found\", \"Country Standards\", MessageBoxButton.OK, MessageBoxImage.Information);
btnClear_Click(null, null);
}
}
The step objUDMCountryStandards.Country = txtSearchCountry.Text.Trim() != string.Empty ? txtSearchCountry.Text : null; in get grid data throws exception
The calling thread cannot access this object because a different thread owns it.
What\'s wrong here?
回答1:
This is a common problem with people getting started. Whenever you update your UI elements from a thread other than the main thread, you need to use:
this.Dispatcher.Invoke(() =>
{
...// your code here.
});
You can also use control.Dispatcher.CheckAccess() to check whether the current thread owns the control. If it does own it, your code looks as normal. Otherwise, use above pattern.
回答2:
Another good use for Dispatcher.Invoke is for immediately updating the UI in a function that performs other tasks:
// Force WPF to render UI changes immediately with this magic line of code...
Dispatcher.Invoke(new Action(() => { }), DispatcherPriority.ContextIdle);
I use this to update button text to "Processing..." and disable it while making WebClient requests.
回答3:
To add my 2 cents, the exception can occur even if you call your code through System.Windows.Threading.Dispatcher.CurrentDispatcher.Invoke().
The point is that you have to call Invoke() of the Dispatcher of the control that you're trying to access, which in some cases may not be the same as System.Windows.Threading.Dispatcher.CurrentDispatcher. So instead you should use YourControl.Dispatcher.Invoke() to be safe. I was banging my head for a couple of hours before I realized this.
Update
For future readers, it looks like this has changed in the newer versions of .NET (4.0 and above). Now you no longer have to worry about the correct dispatcher when updating UI-backing properties in your VM. WPF engine will marshal cross-thread calls on the correct UI thread. See more details here. Thanks to @aaronburro for the info and link. You may also want to read our conversation below in comments.
回答4:
If you encounter this problem and UI Controls were created on a separate worker thread when working with BitmapSource or ImageSource in WPF, call Freeze() method first before passing the BitmapSource or ImageSource as a parameter to any method. Using Application.Current.Dispatcher.Invoke() does not work in such instances
回答5:
this happened with me because I tried to access UI component in another thread insted of UI thread
like this
private void button_Click(object sender, RoutedEventArgs e)
{
new Thread(SyncProcces).Start();
}
private void SyncProcces()
{
string val1 = null, val2 = null;
//here is the problem
val1 = textBox1.Text;//access UI in another thread
val2 = textBox2.Text;//access UI in another thread
localStore = new LocalStore(val1);
remoteStore = new RemoteStore(val2);
}
to solve this problem, wrap any ui call inside what Candide mentioned above in his answer
private void SyncProcces()
{
string val1 = null, val2 = null;
this.Dispatcher.Invoke((Action)(() =>
{//this refer to form in WPF application
val1 = textBox.Text;
val2 = textBox_Copy.Text;
}));
localStore = new LocalStore(val1);
remoteStore = new RemoteStore(val2 );
}
回答6:
For some reason Candide's answer didn't build. It was helpful, though, as it led me to find this, which worked perfectly:
System.Windows.Threading.Dispatcher.CurrentDispatcher.Invoke((Action)(() =>
{
//your code here...
}));
回答7:
You need to Update in to the UI, So use
Dispatcher.BeginInvoke(new Action(() => {GetGridData(null, 0)}));
回答8:
I also found that System.Windows.Threading.Dispatcher.CurrentDispatcher.Invoke() is not always dispatcher of target control, just as dotNet wrote in his answer. I didn't had access to control's own dispatcher, so I used Application.Current.Dispatcher and it solved the problem.
回答9:
The problem is that you are calling GetGridData from a background thread. This method accesses several WPF controls which are bound to the main thread. Any attempt to access them from a background thread will lead to this error.
In order to get back to the correct thread you should use SynchronizationContext.Current.Post. However in this particular case it seems like the majority of the work you are doing is UI based. Hence you would be creating a background thread just to go immediately back to the UI thread and do some work. You need to refactor your code a bit so that it can do the expensive work on the background thread and then post the new data to the UI thread afterwards
回答10:
As mentioned here, Dispatcher.Invoke could freeze the UI. Should use Dispatcher.BeginInvoke instead.
Here is a handy extension class to simplify the checking and calling dispatcher invocation.
Sample usage: (call from WPF window)
this Dispatcher.InvokeIfRequired(new Action(() =>
{
logTextbox.AppendText(message);
logTextbox.ScrollToEnd();
}));
Extension class:
using System;
using System.Windows.Threading;
namespace WpfUtility
{
public static class DispatcherExtension
{
public static void InvokeIfRequired(this Dispatcher dispatcher, Action action)
{
if (dispatcher == null)
{
return;
}
if (!dispatcher.CheckAccess())
{
dispatcher.BeginInvoke(action, DispatcherPriority.ContextIdle);
return;
}
action();
}
}
}
回答11:
This works for me.
new Thread(() =>
{
Thread.CurrentThread.IsBackground = false;
Application.Current.Dispatcher.BeginInvoke(DispatcherPriority.Background, (SendOrPostCallback)delegate {
//Your Code here.
}, null);
}).Start();
回答12:
Also, another solution is ensuring your controls are created in UI thread, not by a background worker thread for example.
回答13:
I kept getting the error when I added cascading comboboxes to my WPF application, and resolved the error by using this API:
using System.Windows.Data;
private readonly object _lock = new object();
private CustomObservableCollection<string> _myUiBoundProperty;
public CustomObservableCollection<string> MyUiBoundProperty
{
get { return _myUiBoundProperty; }
set
{
if (value == _myUiBoundProperty) return;
_myUiBoundProperty = value;
NotifyPropertyChanged(nameof(MyUiBoundProperty));
}
}
public MyViewModelCtor(INavigationService navigationService)
{
// Other code...
BindingOperations.EnableCollectionSynchronization(AvailableDefectSubCategories, _lock );
}
For details, please see https://msdn.microsoft.com/query/dev14.query?appId=Dev14IDEF1&l=EN-US&k=k(System.Windows.Data.BindingOperations.EnableCollectionSynchronization);k(TargetFrameworkMoniker-.NETFramework,Version%3Dv4.7);k(DevLang-csharp)&rd=true
来源：https://stackoverflow.com/questions/9732709/the-calling-thread-cannot-access-this-object-because-a-different-thread-owns-it