Question

我正在为Win 8.1（WinRT）做一个Windows应用商店应用。该应用程序的其中一个页面是地址簿。在某些情况下，应用会收到推送通知。其中一个可能是某个联系人有一个新的图片。当应用程序处理推送通知（不是推送通知的后台任务，工作正常）时，它会从推送通知中指定的链接下载新图像，并触发应该使用新图像更新UI的事件。图像存储在LocalFolder（ApplicationData.Current.LocalFolder）中。触发事件后，UI会更新，但现在没有相应联系人的任何图片。重新启动应用程序后，将显示图片。当应用程序运行时，我还打开了Windows资源管理器以查看文件是否已下载。一个奇怪的事情是，在应用程序重新启动（或停止）之前，新图片没有缩略图。我真的无法弄清楚为什么我需要重新启动应用程序才能显示图片。图像非常小，约为40-60KB。通过重置绑定到引发PropertyChanged的属性的ItemsSource来实现更新。可以看出ItemsSource已设置，因为短暂闪烁，但现在已更新的项目没有图片。

以下是执行下载的代码：

public async Task GetContactImage(String[] pushContent)
    {
        var folder = ApplicationData.Current.LocalFolder;
        var contactImagesfolder = await folder.CreateFolderAsync("ContactImages", CreationCollisionOption.OpenIfExists);

        HttpClient httpClient = new HttpClient();
        // Increase the max buffer size for the response so we don't get an exception with so many web sites
        httpClient.MaxResponseContentBufferSize = 256000;
        HttpResponseMessage response = await httpClient.GetAsync(pushContent[2]);

        StorageFile picture = await contactImagesfolder.CreateFileAsync(pushContent[2].Split('/').Last(), CreationCollisionOption.ReplaceExisting);
        IRandomAccessStream pictureStream = await picture.OpenAsync(FileAccessMode.ReadWrite);
        DataWriter writer = new DataWriter(pictureStream.GetOutputStreamAt(0));
        writer.WriteBytes(await response.Content.ReadAsByteArrayAsync());
        await writer.StoreAsync();
        writer.DetachStream();
        await pictureStream.FlushAsync();

        pictureStream.Dispose();
        writer.Dispose();

        Dal.Instance.UpdateContactImage(pushContent[1], pushContent[2]);
    }

相应的XAML，它是ListView（duh）的DataTemplate：

<Image Height="128" Width="128" Source="{Binding Converter={StaticResource contactImageConverter}}" />

我用来设置Source属性的转换器：

public object Convert(object value, Type targetType, object parameter, string language)
    {
        var contact = value as Contact;
        String imagePath = "ms-appx:///Assets/UnknownMan.png";
        if (contact != null)
        {
            if (contact.Image != null && contact.Image != "" && contact.Image != "Unknow_man.png")
            {
                imagePath = "ms-appdata:///local/ContactImages/" + contact.Image.Split('/').Last();                    
            }
        }

        return imagePath;
    }

非常感谢你的帮助！

Answer 1

事实证明，将文件保存到文件系统的方法创建了某种句柄，这样就不允许应用加载图像。我所做的是改变保存文件的方法。

StorageFolder folder = ApplicationData.Current.LocalFolder;
StorageFolder contactImagesfolder = await folder.CreateFolderAsync("ContactImages", CreationCollisionOption.OpenIfExists);
StorageFile picture = await contactImagesfolder.CreateFileAsync(imageURL.Split('/').Last(), CreationCollisionOption.FailIfExists);

HttpClient httpClient = new HttpClient();
// Increase the max buffer size for the response so we don't get an exception with so many web sites
httpClient.MaxResponseContentBufferSize = 256000;
HttpResponseMessage response = await httpClient.GetAsync(imageURL);

var responseByteArray = await response.Content.ReadAsByteArrayAsync();
await FileIO.WriteBytesAsync(picture, responseByteArray);

Dal.Instance.UpdateContactImage(contactID, imageURL);

下载后未加载WinRT Image XAML

1 个答案: