c# - 在 WP8 中从 Web URL 加载图像

Question

我有一张指定网址的网页图片，可以在浏览器中浏览。

我试图从 web url 检索它，当程序转到 bitmapImage.SetSource(ms); 我得到一个异常“

ex = {System.Exception: The component cannot be found. (Exception from HRESULT: 0x88982F50)
   at MS.Internal.XcpImports.CheckHResult(UInt32 hr)
   at MS.Internal.XcpImports.BitmapSource_SetSource(BitmapSource bitmapSource, CValue& byteStream)
   at System.Wi...

"我确实在 stackoverflow 上搜索了其他问题……但对此没有帮助。谁能帮帮我？

byte数组确实有数据，运行时调试返回imageByteArray = {byte[1227]};我的选择是将字节数组转换为 BitmapImage 时发生异常。

在 httpclient 包装器类中:

public static async Task<Byte[]> GetWebImageByImageName(string ImageName)
        {
            //Uri imageServerUril = new Uri(ImageName);

          var requestMessage = new HttpRequestMessage(HttpMethod.Get, ImageName);
        var responseMessage = await client.SendAsync(requestMessage, HttpCompletionOption.ResponseHeadersRead);

        var responseData = await responseMessage.Content.ReadAsByteArrayAsync();
        return responseData;

        }

在 View 模型中:

private async void ReadArticleList(int pageNumber)
        {
                string webURL = "http://....."; // the web URL is no problem
              try
              {
                    byte[] imageByteArray = await CollectionHttpClient.GetWebImageByImageName(webURL);// 


                //Convert it to BitmapImage               
                    using (MemoryStream ms = new MemoryStream(imageByteArray))
                    {
                        BitmapImage bitmapImage = new BitmapImage();
                        bitmapImage.CreateOptions = BitmapCreateOptions.DelayCreation;
                        bitmapImage.SetSource(ms); // the exception got here 
                        item.BitImage = bitmapImage;
                    }



                IsLoading = false;


            }
            catch(Exception ex)
            {
                if (ex.HResult == -2146233088 && ex.Message.Equals("Response status code does not indicate success: 404 ()."))
                {
                    MessageBox.Show("The network is not set right. Internet cannot be accessed.");
                }
                else
                {
                    MessageBox.Show("sorry, no data.");
                }

                IsLoading = false;
            }

        }

* 用于详细信息 *

1. BitImage 是 BitmapImage 的实例；
2. item.BitImage: item 是 Article 的一个实例
3. 图片格式为JPEG

文章模型如下:

public class Article : INotifyPropertyChanged
    {
        private long _Id;
        public long ID
        {
            get { return _Id; }
            set
            {
                if (_Id != value)
                {
                    _Id = value;
                    NotifyPropertyChanged("ID");
                }
            }
        }


        private string _subject;
        public string Subject
        {
            get
            {
                return _subject;
            }
            set
            {
                if (_subject != value)
                {
                    _subject = value;
                    NotifyPropertyChanged("Subject");
                }
            }
        }

        private string _words;
        public string Words
        {
            get
            {
                return _words;
            }
            set
            {
                if (_words != value)
                {
                    _words = value;
                    NotifyPropertyChanged("Words");
                }
            }
        }

        private DateTime _publishDate;
        public DateTime PublishDate
        {
            get
            { return _publishDate; }
            set
            {
                if (_publishDate != value)
                {
                    _publishDate = value;
                    NotifyPropertyChanged("PublishDate");
                }
            }
        }

        public List<string> ImagePathList = new List<string>();

        public BitmapImage BitImage = new BitmapImage();

        private string _firstImage;
        public string FirstImage
        {
            get
            {
                return _firstImage;
            }
            set
            {
                if (_firstImage != value)
                {
                    _firstImage = value;
                    NotifyPropertyChanged();
                }
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
        {
            PropertyChangedEventHandler handler = PropertyChanged;
            if (null != handler)
            {
                handler(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }

Answer 1

如果您只想显示来自远程服务器的图像而不保存它，请执行以下操作:

imageControl1.Source = new BitmapImage(new Uri("http://delisle.saskatooncatholic.ca/sites/delisle.saskatooncatholic.ca/files/sample-1.jpg", UriKind.Absolute));

如果要将图像保存到 IsolatedStorage，可以执行以下操作:

WebClient webClientImg = new WebClient();
webClientImg.OpenReadCompleted += new OpenReadCompletedEventHandler(client_OpenReadCompleted);
webClientImg.OpenReadAsync(new Uri("http://delisle.saskatooncatholic.ca/sites/delisle.saskatooncatholic.ca/files/sample-1.jpg", UriKind.Absolute));

    void client_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
    {
        isSpaceAvailable = IsSpaceIsAvailable(e.Result.Length);
        if (isSpaceAvailable)
        {
            SaveToJpeg(e.Result);
        }
        else
        {
            MessageBox.Show("You are running low on storage space on your phone. Hence the image will be loaded from the internet and not saved on the phone.", "Warning", MessageBoxButton.OK);
        }
    }

检查IsolatedStorage空间是否可用的功能，否则将不会下载图像。

    private bool IsSpaceIsAvailable(long spaceReq)
    {
        using (var store = IsolatedStorageFile.GetUserStoreForApplication())
        {
            long spaceAvail = store.AvailableFreeSpace;
            if (spaceReq > spaceAvail)
            {
                return false;
            }
            return true;
        }
    }

如果空间可用，使用以下函数将图像保存到 IsolatedStorage:

    private void SaveToJpeg(Stream stream)
    {
        using (IsolatedStorageFile iso = IsolatedStorageFile.GetUserStoreForApplication())
        {
            using (IsolatedStorageFileStream isostream = iso.CreateFile("image1.jpg"))
            {
                BitmapImage bitmap = new BitmapImage();
                bitmap.SetSource(stream);
                WriteableBitmap wb = new WriteableBitmap(bitmap);
                // Encode WriteableBitmap object to a JPEG stream. 
                Extensions.SaveJpeg(wb, isostream, wb.PixelWidth, wb.PixelHeight, 0, 85);
                isostream.Close();

                LoadImageFromIsolatedStorage(); //Load recently saved image into the image control
            }
        }
    }

从 IsolatedStorage 加载图像到图像控件中:

    private void LoadImageFromIsolatedStorage()
    {
        byte[] data;

        try
        {
            using (IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication())
            {
                using (IsolatedStorageFileStream isfs = isf.OpenFile("image1.jpg", FileMode.Open, FileAccess.Read))
                {
                    data = new byte[isfs.Length];
                    isfs.Read(data, 0, data.Length);
                    isfs.Close();
                }
            }
            MemoryStream ms = new MemoryStream(data);
            BitmapImage bi = new BitmapImage();
            bi.SetSource(ms);
            imageControl1.Source = bi;
        }
        catch
        {
        }
    }

Image taken randomly from Google Search. Credits to the image lie to the owner.

希望这对您有所帮助。 :)