WP7 - 如何检查图像是否已加载

我正在尝试将一些数据绑定到 wp7 列表框（使用自定义项模板），其中包括每个条目的缩略图。问题是 - 我遇到了一个问题 - 当链接的图像重定向到 404 页面时 - 结果我得到一个空图像，坦率地说 - 我不知道如何检查加载的数据是否是正确的图像或不......这是我现在使用的代码：

<ListBox.ItemTemplate>
                    <DataTemplate>
                        <StackPanel Orientation="Horizontal">
                            <Grid Height="62"
                                  Width="62">
                                <Image Stretch="UniformToFill"
                                       HorizontalAlignment="Center"
                                       VerticalAlignment="Center">
                                    <Image.Source>
                                        <BitmapImage UriSource="{Binding MiniImage}"
                                                     CreateOptions="DelayCreation, BackgroundCreation" />
                                    </Image.Source>
                                </Image>
                            </Grid>
                            <StackPanel HorizontalAlignment="Center"
                                        VerticalAlignment="Center">
                                <TextBlock Text="{Binding Title}"
                                           Margin="12,4,0,0"
                                           FontSize="26"
                                           FontFamily="Segoe WP Bold" />
                                <TextBlock Text="{Binding PubDate}"
                                           Margin="12,0,0,9"
                                           FontSize="16"
                                           FontStyle="Italic"
                                           Padding="5,0,0,0"
                                           FontFamily="Segoe WP"
                                           Opacity="0.5" />
                            </StackPanel>
                        </StackPanel>
                    </DataTemplate>
                </ListBox.ItemTemplate>

下面是背后的代码：

foreach (var item in RssFeedItems)
        {
            var inputString = item.Description;
            var tempImageList = new List<string>();
            var inputStringBuilt = new StringBuilder(item.Description);
            var temp = 1;
            while (temp > 0)
            {
                var img = inputString.IndexOf("<img", StringComparison.Ordinal);
                var src = inputString.IndexOf("src", img, StringComparison.Ordinal);
                var quot = inputString.IndexOf('"', src + 5);
                var len = quot - (src + 5);
                var sub = len > 0 ? inputString.Substring(src + 5, len) : null;
                tempImageList.Add(sub);
                var closingBracket = inputString.IndexOf(">", src, StringComparison.Ordinal);
                inputStringBuilt.Clear();
                inputStringBuilt.Append(inputString);
                inputStringBuilt.Remove(img, closingBracket - img);
                inputString = inputStringBuilt.ToString();
                temp = inputString.IndexOf("<img", StringComparison.Ordinal);
            }
            item.MiniImage = tempImageList[0] ?? "ApplicationIcon.png";
            var f = tempImageList.IndexOf(null) - 1;
            while (f >= 0)
            {
                PostImages.Add(tempImageList[f]);
                f--;
            }
            tempImageList.Clear();
            FirstListBox.Items.Add(item);
        }

有什么想法吗？