相关疑难解决方法(0)

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 …

为什么我不能在以下代码中创建CroppedBitmap？我有一个例外:

调用线程无法访问此对象,因为另一个线程拥有它.

如果我将代码更改为

CroppedBitmap cb = new CroppedBitmap(new WriteableBitmap(bf), new Int32Rect(1, 1, 5, 5));

异常消失了吗？为什么？

代码1,例外情况cb.Freeze():

public MainWindow()
{
    InitializeComponent();

    ThreadPool.QueueUserWorkItem((o) =>
        {
            //load a large image file
            var bf = BitmapFrame.Create(
                new Uri("D:\\1172735642.jpg"),
                BitmapCreateOptions.None,
                BitmapCacheOption.None);
            bf.Freeze();
            Dispatcher.BeginInvoke(
                new Action(() =>
                    {
                        CroppedBitmap cb = new CroppedBitmap(bf, new Int32Rect(1,1,5,5));
                        cb.Freeze();
                        //set Image's source to cb....
                    }), 
                    DispatcherPriority.ApplicationIdle);
         }
    );
}

代码2,有效:

    ThreadPool.QueueUserWorkItem((o) =>
    {
        var bf = BitmapFrame.Create(
                new Uri("D:\\1172740755.jpg"),
                BitmapCreateOptions.None,
                //BitmapCreateOptions.DelayCreation,
                BitmapCacheOption.None);
        bf.Freeze();
        var wb = new …