How to capture screen programatically in windows p

问题:

Any Idea how to capture screen in SDK 8.1 windows phone from code? For windows phone 7.5 i have seen the code and tried to use, but it failed. :(

回答1:

You can use a RenderTargetBitmap and pass it a FrameworkElement that represents the page and then render a bitmap from that.

private async Task<RenderTargetBitmap> CreateBitmapFromElement(FrameworkElement uielement)
{
    try
    {
        var renderTargetBitmap = new RenderTargetBitmap();
        await renderTargetBitmap.RenderAsync(uielement);

        return renderTargetBitmap;
    }
    catch (Exception ex)
    {
        System.Diagnostics.Debug.WriteLine(ex);
    }

    return null;
}

try something like:

private async void ButtonBase_OnClick(object sender, RoutedEventArgs e)
{
    this.imagePreview.Source = await CreateBitmapFromElement(this);
}

where the XAML on your page is:

<Grid x:Name="controlsGrid">
    <Button Click="ButtonBase_OnClick">take screenshot</Button>
    <Image x:Name="imagePreview"
           Height="200" VerticalAlignment="Bottom"
           Stretch="UniformToFill" />
</Grid>

回答2:

To save the rendered image as an image file, we have to send it to a stream, encode it to the file type we want.

This is a method we can use for that (It takes in a UI element, a stream and a Guid):

//Creates RenderTargetBitmap from UI Element 
 async Task<RenderTargetBitmap> CaptureToStreamAsync(FrameworkElement uielement, IRandomAccessStream stream, Guid encoderId)
  {
      try
      {
          var renderTargetBitmap = new RenderTargetBitmap();
          await renderTargetBitmap.RenderAsync(uielement);
          var pixels = await renderTargetBitmap.GetPixelsAsync();
          var logicalDpi = DisplayInformation.GetForCurrentView().LogicalDpi;
          var encoder = await BitmapEncoder.CreateAsync(encoderId, stream);
          encoder.SetPixelData(
              BitmapPixelFormat.Bgra8,
              BitmapAlphaMode.Ignore,
              (uint)renderTargetBitmap.PixelWidth,
              (uint)renderTargetBitmap.PixelHeight,
              logicalDpi,
              logicalDpi,
              pixels.ToArray());

          await encoder.FlushAsync();
          return renderTargetBitmap;        
  }

We can then use the FileSavePicker class on Windows Phone 8.1 to decide the filetype, name and saving location.

void CreateFileSavePicker()
    {
        //Create the picker object
        FileSavePicker savePicker = new FileSavePicker();

        // Dropdown of file types the user can save the file as   
        savePicker.FileTypeChoices.Add
            (
            "Image", new List<string>() { ".jpg" });
        // Default file name if the user does not type one in or select // a file to replace
        savePicker.SuggestedFileName = "Screenshot";
        savePicker.SuggestedStartLocation = PickerLocationId.PicturesLibrary; 

        //// Open the picker for the user to pick a file
        savePicker.ContinuationData["Operation"] = "SomeDataOrOther";
        savePicker.PickSaveFileAndContinue();

    }

When the user has picked the file location, it comes back to ContinueFileSavePicker.

public async void      ContinueFileSavePicker(Windows.ApplicationModel.Activation.FileSavePickerContinu ationEventArgs args)
 {
        StorageFile file = args.File;
        if (file != null)
{
            // Prevent updates to the remote version of the file until we finish making changes and call CompleteUpdatesAsync.
            CachedFileManager.DeferUpdates(file);

            Guid encoderId = BitmapEncoder.JpegEncoderId;

            try
            {
                using (var stream = await file.OpenAsync(FileAccessMode.ReadWrite))
                {
                    await CaptureToStreamAsync(LayoutRoot, stream, encoderId);

                }
            }
            catch (Exception ex)
            {
                DisplayMessage(ex.Message);
            }
}
}

More details here.