The calling thread cannot access this object because a different thread owns it

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?

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.

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.

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.

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

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 );
}