C# StorageFolder.OpenStreamForWriteAsync方法代碼示例

    public async Task Init(string appname) {
      var devices = Windows.Storage.KnownFolders.RemovableDevices;
      var sdCards = await devices.GetFoldersAsync();
      if (sdCards.Count == 0) return;
      _SDCard = sdCards[0];
      string foldername = string.Format("{0}_Log", appname);
      _LogFolder = await _SDCard.CreateFolderAsync(foldername, CreationCollisionOption.OpenIfExists);

      _FileName = string.Format("{0:yyyy-MM-dd}.txt", DateTime.Now);
      _Stream = await _LogFolder.OpenStreamForWriteAsync(_FileName, CreationCollisionOption.OpenIfExists);

    }

        async Task GenerateIcon(AppInfo appInfo, IconInfo iconInfo, StorageFolder folder)
        {
            // Draw the icon image into a command list.
            var commandList = new CanvasCommandList(device);

            using (var ds = commandList.CreateDrawingSession())
            {
                appInfo.DrawIconImage(ds, iconInfo);
            }

            ICanvasImage iconImage = commandList;

            // Rasterize into a rendertarget.
            var renderTarget = new CanvasRenderTarget(device, iconInfo.Width, iconInfo.Height, 96);

            using (var ds = renderTarget.CreateDrawingSession())
            {
                // Initialize with the appropriate background color.
                ds.Clear(iconInfo.TransparentBackground ? Colors.Transparent : appInfo.BackgroundColor);

                // Work out where to position the icon image.
                var imageBounds = iconImage.GetBounds(ds);

                imageBounds.Height *= 1 + iconInfo.BottomPadding;

                float scaleUpTheSmallerIcons = Math.Max(1, 1 + (60f - iconInfo.Width) / 50f);

                float imageScale = appInfo.ImageScale * scaleUpTheSmallerIcons;

                var transform = Matrix3x2.CreateTranslation((float)-imageBounds.X, (float)-imageBounds.Y) *
                                Utils.GetDisplayTransform(renderTarget.Size.ToVector2(), new Vector2((float)imageBounds.Width, (float)imageBounds.Height)) *
                                Matrix3x2.CreateScale(imageScale, renderTarget.Size.ToVector2() / 2);

                if (iconInfo.Monochrome)
                {
                    // Optionally convert to monochrome.
                    iconImage = new DiscreteTransferEffect
                    {
                        Source = new Transform2DEffect
                        {
                            Source = new LuminanceToAlphaEffect { Source = iconImage },
                            TransformMatrix = transform
                        },

                        RedTable   = new float[] { 1 },
                        GreenTable = new float[] { 1 },
                        BlueTable  = new float[] { 1 },
                        AlphaTable = new float[] { 0, 1 }
                    };
                }
                else
                {
                    ds.Transform = transform;

                    // Optional shadow effect.
                    if (appInfo.AddShadow)
                    {
                        var shadow = new ShadowEffect
                        {
                            Source = iconImage,
                            BlurAmount = 12,
                        };

                        ds.DrawImage(shadow);
                    }
                }

                // draw the main icon image.
                ds.DrawImage(iconImage);
            }

            // Save to a file.
            using (var stream = await folder.OpenStreamForWriteAsync(iconInfo.Filename, CreationCollisionOption.ReplaceExisting))
            {
                await renderTarget.SaveAsync(stream.AsRandomAccessStream(), CanvasBitmapFileFormat.Png);
            }
        }