无效的跨线程访问

Question

当我尝试在我的cam_CaptureImageAvailable方法中使用BitMapImage时，出现了无效的跨线程访问错误，我尝试使用Dispatcher解决，但它给了我一个无法访问关闭的Stream错误，出现了System.ObjectDisposedException未处理异常。

// Informs when full resolution picture has been taken, saves to local media library and isolated storage.
    void cam_CaptureImageAvailable(object sender, Microsoft.Devices.ContentReadyEventArgs e)
    {

        string fileName = folderName+"\\MyImage" + savedCounter + ".jpg";

        try
        {   // Write message to the UI thread.
            Deployment.Current.Dispatcher.BeginInvoke(delegate()
            {
                txtDebug.Text = "Captured image available, saving picture ," + fileName;
            });

            // Save picture to the library camera roll.
            //library.SavePictureToCameraRoll(fileName, e.ImageStream);


            // Write message to the UI thread.
            Deployment.Current.Dispatcher.BeginInvoke(delegate()
            {
                //txtDebug.Text = "Picture has been saved.";

            });

            // Set the position of the stream back to start
            e.ImageStream.Seek(0, SeekOrigin.Begin);


            // Save picture as JPEG to isolated storage.
            using (IsolatedStorageFile isStore = IsolatedStorageFile.GetUserStoreForApplication())
            {
                using (IsolatedStorageFileStream targetStream = isStore.OpenFile(fileName, FileMode.Create, FileAccess.Write))
                {

                    // Initialize the buffer for 4KB disk pages.
                    byte[] readBuffer = new byte[4096];
                    int bytesRead = -1;

                    // Copy the image to isolated storage. 
                    while ((bytesRead = e.ImageStream.Read(readBuffer, 0, readBuffer.Length)) > 0)
                    {
                        targetStream.Write(readBuffer, 0, bytesRead);

                    }

                }

                var bitmapImage = new BitmapImage(); 
                bitmapImage.SetSource(e.ImageStream); 
                WriteableBitmap wb = new WriteableBitmap(bitmapImage);
                IsolatedStorageFile myStore = IsolatedStorageFile.GetUserStoreForApplication(); 
                using (IsolatedStorageFileStream myFileStream = myStore.CreateFile(fileName)) 
                { 
                    wb.SaveJpeg(myFileStream, 10, 10, 0, 70); 
                }

            }





        }
        finally
        {
            // Close image stream
            e.ImageStream.Close();
        }

    }

Tried this as well

Deployment.Current.Dispatcher.BeginInvoke(delegate()
                {
                    var bitmapImage = new BitmapImage();
                    bitmapImage.SetSource(e.ImageStream);
                    WriteableBitmap wb = new WriteableBitmap(bitmapImage);
                    IsolatedStorageFile myStore = IsolatedStorageFile.GetUserStoreForApplication();
                    using (IsolatedStorageFileStream myFileStream = myStore.CreateFile(fileName))
                    {
                        wb.SaveJpeg(myFileStream, 10, 10, 0, 70);//compressing image
                    }
                });

有人能帮我吗？非常感激，谢谢。

- M_K

Answer 1

你需要在UI线程上创建BitmapImage和WriteableBitmap，因为它们是DependencyObject。

你之所以会得到ObjectDisposedException错误是因为当调度程序处理你的请求时，图像的流已经关闭了。

你尝试将该代码移动到你的调度程序调用中了吗？

 e.ImageStream.Close();

调度程序的代码不会立即执行，而是在以后的某个时间点执行，但您已经关闭了流。

如果这种方法不起作用，您可以通过在“CaptureImageAvailable”中将流读入内存，然后将该“MemoryStream”作为源传递给您的“BitmapImage”，来解决问题。

- thumbmunkeys

---

嗨，pivotnig，我正在使用内存流并且它可以工作，但是每次我拍照时只能得到第一张图片，这是我正在使用的代码 e.ImageStream.Seek(0, SeekOrigin.Begin);e.ImageStream.CopyTo(ms); 并且在调度程序中我有 var bitmapImage = new BitmapImage();bitmapImage.SetSource(ms);WriteableBitmap wb = new WriteableBitmap(bitmapImage); 谢谢您的帮助。 - M_K

每次拍照时我只能得到第一张图片。 - M_K

没问题，我把Memory Stream作为全局变量了 :) - M_K