(Metro学习三)图片uri保存到本地图片库

已知网络上图片的uri地址，如何将网络图片保存到本地呢？代码如下：

private async Task SaveImageFromUrl(string uri, string filename)
        {

            var rass = RandomAccessStreamReference.CreateFromUri(new Uri(uri));
            IRandomAccessStream inputStream = await rass.OpenReadAsync();
            Stream input = WindowsRuntimeStreamExtensions.AsStreamForRead(inputStream.GetInputStreamAt(0));
            try
            {
                //获取图片扩展名的Guid
                StorageFolder folder = KnownFolders.PicturesLibrary;
                StorageFile outputFile = await folder.CreateFileAsync(filename, CreationCollisionOption.ReplaceExisting);
                using (IRandomAccessStream outputStream = await outputFile.OpenAsync(FileAccessMode.ReadWrite))
                {
                    Stream output = WindowsRuntimeStreamExtensions.AsStreamForWrite(outputStream.GetOutputStreamAt(0));
                    await input.CopyToAsync(output);
                    output.Dispose();
                    input.Dispose();
                }
            }
            catch (Exception)
            {
            }
        }

根据图片uri保存到本地的函数，即以上为图片uri和图片名称的转换，另以下三种转换：

1、FileName转换为Stream，图片可为本地图片，也可为应用程序中图片

private async Task<Stream> ImageNameToStream(string filename)
        {
            try
            {
                ////本地图片库
                //StorageFolder folder = KnownFolders.PicturesLibrary;//本地图片库
                //StorageFile storagefile = await folder.GetFileAsync(filename);

                //应用程序Images文件夹图片
                Uri _baseUri = new Uri("ms-appx:///");
                Uri uri = new Uri(_baseUri, "../Images/" + filename);
                StorageFile storagefile = await StorageFile.GetFileFromApplicationUriAsync(uri);


                IRandomAccessStream irandom = await storagefile.OpenAsync(FileAccessMode.Read);
                Stream outPutstream = irandom.GetInputStreamAt(0).AsStreamForRead();
                return outPutstream;
            }
            catch (Exception ex)
            {
                return null;
            }
        }

2、Stream转换成文件，图片保存到本地

private async Task StreamToFileName(Stream inputstream, string filename)
        {
            try
            {
                StorageFolder folder = KnownFolders.PicturesLibrary;
                StorageFile outputFile = await folder.CreateFileAsync(filename, CreationCollisionOption.ReplaceExisting);
                using (IRandomAccessStream output = await outputFile.OpenAsync(FileAccessMode.ReadWrite))
                {
                    Stream outputstream = WindowsRuntimeStreamExtensions.AsStreamForWrite(output.GetOutputStreamAt(0));
                    await inputstream.CopyToAsync(outputstream);
                    outputstream.Dispose();
                    inputstream.Dispose();
                }
            }
            catch (Exception ex)
            {
            }
        }

3、图片Uri转换成流

private async Task<Stream> UriToStream(string uri)
        {
            var rass = RandomAccessStreamReference.CreateFromUri(new Uri(uri));
            IRandomAccessStream inputStream = await rass.OpenReadAsync();
            Stream input = WindowsRuntimeStreamExtensions.AsStreamForRead(inputStream.GetInputStreamAt(0));
            return input;
        }

若有其他流与Metro流之间的转换,参考http://www.cnblogs.com/jing870812/archive/2012/04/12/2444870.html