WP 8.1从http请求绑定图像 [英] WP 8.1 Binding image from a http request

问题描述

我有一个包含从HTTP GET请求DATAS和图像的ListView项。我可以在ListView中显示所有的数据，除了照片。用于获取图像我必须做出一个单独的HTTP GET请求。我可以用这个code显示图像：

I have a ListView item which contains datas and images from a http GET request. I can display all of data in the ListView, except the picture. For getting the image I have to make a separate http GET request. I can display an image with this code:

private async void DisplayPicture()
{
    var ims = new InMemoryRandomAccessStream();
    var dataWriter = new DataWriter(ims);
    dataWriter.WriteBytes(App.answer.picture);
    await dataWriter.StoreAsync();
    ims.Seek(0);
    BitmapImage bitmap = new BitmapImage();
    bitmap.CreateOptions = BitmapCreateOptions.IgnoreImageCache;
    bitmap.SetSource(ims);
}

但是，如果我想在ListView使用绑定与该不起作用。
这里是code是我的尝试：

But this doesn't work if I would like to use in a ListView with Binding. Here is the code what I tried:

public class BinaryToImageSourceConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, string language)
    {
        if (value != null && value is byte[])
        {
            var bytes = value as byte[];
            var ims = new InMemoryRandomAccessStream();
            var dataWriter = new DataWriter(ims);
            dataWriter.WriteBytes(bytes);
            //await dataWriter.StoreAsync();
            ims.Seek(0);
            BitmapImage bitmap = new BitmapImage();
            bitmap.SetSource(ims);
            //var ims = new MemoryStream(bytes);
            //var image = new BitmapImage();
            //image.SetSource(stream);
            //stream.Close();
            return bitmap;
        }
        return null;
    }
    public object ConvertBack(object value, Type targetType, object parameter, string language)
    {
        throw new NotImplementedException();
    }
}

主要的问题是，我得到了来自服务器的byte []（字节阵列）的形象，只有上面的code可以在WP8.1显示。所以，我必须使用 dataWriter.StoreAsync（）方法，但如果我使用它，我必须使用异步 ，它必须是无效的。但void返回值不为我好，由于具有约束力。

The main problem is that I get the image in byte[] (bytearray) from the server, and only the above code can display it on WP8.1. So I have to use the dataWriter.StoreAsync() method, but if I use it, I have to use async, which must be void. But the void return value is not good for me due to the binding.

您可以看到原来的code是我的注释去掉，但我不能使用它，因为输入值image.SetSource（）必须是一个RandomAccessStream。所以，我没有任何想法，我怎么能解决这个问题。

You can see the original code what I uncommented, but I cannot use it, because the input value for image.SetSource() must be a RandomAccessStream. So I don't have any idea how I can solve this problem.

推荐答案

如果你想绑定和使用异步方法，那么一个使工作方式是设置的的DataContext 的到的任务的并绑定到其的结果的。 Stepen克利里写道有关一个很好的文章。你还会发现在 href=\"http://stackoverflow.com/a/15007717/2681948\">他的回答。

If you want to make binding and use asynchronous method, then one way to make it work is to set DataContext to Task and bind to its Result. Stepen Cleary wrote a nice article about that. You will also find some useful information in his answer here.

这是这个问题的答案我已经建立一个样品，我想你可以修改，以满足您的需求基础。写的转换的将返回的 TaskCompletionNotifier 的（见上斯蒂芬的回答）：

Basing on that answer I've build a sample, which I think you can modify to fulfill your needs. Write a Converter which will return TaskCompletionNotifier (see Stephen's answer above):

public class WebPathToImage : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, string language)
    {
        if (value == null) return null;
        // the below class you will find in Stephen's answer mentioned above
        return new TaskCompletionNotifier<BitmapImage>(GetImage((String)value));
    }

    public object ConvertBack(object value, Type targetType, object parameter, string language)
    { throw new NotImplementedException(); }

    private async Task<BitmapImage> GetImage(string path)
    {
        HttpClient webCLient = new HttpClient();
        var responseStream = await webCLient.GetStreamAsync(path);
        var memoryStream = new MemoryStream();
        await responseStream.CopyToAsync(memoryStream);
        memoryStream.Position = 0;
        var bitmap = new BitmapImage();
        await bitmap.SetSourceAsync(memoryStream.AsRandomAccessStream());
        return bitmap;
    }
}

，那么你可以定义在XAML绑定：

then you can define binding in XAML:

<Image DataContext="{Binding ImageFromWeb, Converter={StaticResource WebPathToImage}}" Stretch="Uniform" 
       Source="{Binding Result}" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Grid.Row="2"/>

当你设置好一切应该工作 ImageFromWeb ：

Everything should work when you set ImageFromWeb:

ImageFromWeb = @"http://www.onereason.org/wp-content/uploads/2012/02/universe-300x198.jpg";

这篇关于WP 8.1从http请求绑定图像的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！