调用线程无法访问此对象,因为另一个线程拥有它

Question

我的代码如下

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);
    }
}

objUDMCountryStandards.Country = txtSearchCountry.Text.Trim() != string.Empty ? txtSearchCountry.Text : null;获取网格数据的步骤会引发异常

调用线程无法访问此对象,因为另一个线程拥有它.

这有什么不对？

Answer 1

这是人们入门的常见问题.每当您从主线程以外的线程更新UI元素时,您需要使用:

this.Dispatcher.Invoke(() =>
{
    ...// your code here.
});

您还可以使用control.Dispatcher.CheckAccess()检查当前线程是否拥有该控件.如果它拥有它,您的代码看起来很正常.否则,请使用上述模式.

Answer 2

另一个很好的用途Dispatcher.Invoke是在执行其他任务的函数中立即更新UI:

// Force WPF to render UI changes immediately with this magic line of code...
Dispatcher.Invoke(new Action(() => { }), DispatcherPriority.ContextIdle);

我用它将按钮文本更新为" Processing ... "并在发出WebClient请求时禁用它.

Answer 3

要增加2美分,即使您通过代码调用,也会发生异常System.Windows.Threading.Dispatcher.CurrentDispatcher.Invoke().
问题的关键是,你必须调用Invoke()的Dispatcher的的,你要访问的控制,在某些情况下可能不一样System.Windows.Threading.Dispatcher.CurrentDispatcher.所以相反,你应该使用YourControl.Dispatcher.Invoke()安全.在我意识到这一点之前,我正在敲打我的头几个小时.

Answer 4

如果有人试图BitmapSource在WPF和线程中使用并且有相同的消息:ImageSource在传递Freeze()一个线程参数之前先调用方法.

Answer 5

这发生在我身上,因为我试图access UI组成another thread insted of UI thread

像这样

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);
}

要解决这个问题,请将任何ui调用包含在Candide上面提到的答案中

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 );
}

Answer 6

由于某种原因,Candide的答案没有建立.不过,这很有帮助,因为它让我找到了这个,它完美地工作:

System.Windows.Threading.Dispatcher.CurrentDispatcher.Invoke((Action)(() =>
    {
       //your code here...
    }));

Answer 7

您需要更新到UI,所以使用

Dispatcher.BeginInvoke(new Action(() => {GetGridData(null, 0)})); 

Answer 8

这对我有用。

new Thread(() =>
        {

        Thread.CurrentThread.IsBackground = false;
        Application.Current.Dispatcher.BeginInvoke(DispatcherPriority.Background, (SendOrPostCallback)delegate {

          //Your Code here.

        }, null);
        }).Start();

Answer 9

我还发现System.Windows.Threading.Dispatcher.CurrentDispatcher.Invoke()并不总是目标控制的调度程序，正如 dotNet 在他的回答中所写的那样。我无法访问控件自己的调度程序，因此我使用了它Application.Current.Dispatcher，它解决了问题。

Answer 10

正如这里提到的，Dispatcher.Invoke可能会冻结 UI。应Dispatcher.BeginInvoke改为使用。

这是一个方便的扩展类，用于简化检查和调用调度程序调用。

示例用法：（从 WPF 窗口调用）

this Dispatcher.InvokeIfRequired(new Action(() =>
{
    logTextbox.AppendText(message);
    logTextbox.ScrollToEnd();
}));

扩展类：

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();
        }
    }
}