Generate document pages preview
GroupDocs.Signature provides PreviewOptions class to specify different options to manage document pages preview generation process.
Here are the steps to generate document preview with GroupDocs.Signature:
- Create new instance of Signature class and pass source document path as a constructor parameter.
- Instantiate the PreviewOptions object with:
- delegate for each page stream creation (see event handler CreatePageStream);
- image preview format - PNG / JPG / BMP,
- page numbers to process;
- custom size of preview images (if needed).Stream that were created by CreatePageStream delegate will be disposed automatically once after generation of preview image. If you need to implement custom image preview stream disposing you have to pass additional argument ReleaseStream to clean up resources.
- Call GeneratePreviewmethod of Signature class instance and pass PreviewOptions to it.
CreatePageStream delegate implementation
GroupDocs.Signature expects CreatePageStream delegate to obtain each page stream for image preview generation process
private static Stream CreatePageStream(int pageNumber)
{
string imageFilePath = Path.Combine("GeneratePreviewFolder", "image-" + pageNumber.ToString() + ".jpg");
var folder = Path.GetDirectoryName(imageFilePath);
if(!Directory.Exists(folder))
{
Directory.CreateDirectory(folder);
}
return new System.IO.FileStream(imageFilePath, FileMode.Create);
}
ReleasePageStream delegate implementation
private static void ReleasePageStream(int pageNumber, Stream pageStream)
{
pageStream.Dispose();
string imageFilePath = Path.Combine("GeneratePreviewFolder", "image-" + pageNumber.ToString() + ".jpg");
Console.WriteLine("Image file {0} is ready for preview", imageFilePath);
}
Generate document preview from file on local disk
public static void GetPreview()
{
using (Signature signature = new Signature("sample.pdf"))
{
// create preview options object
PreviewOptions previewOption = new PreviewOptions(GeneratePreview.CreatePageStream)
{
PreviewFormat = PreviewOptions.PreviewFormats.JPEG,
};
// generate preview
signature.GeneratePreview(previewOption);
}
}
private static Stream CreatePageStream(int pageNumber)
{
string imageFilePath = Path.Combine("GeneratePreviewFolder", "image-" + pageNumber.ToString() + ".jpg");
var folder = Path.GetDirectoryName(imageFilePath);
if(!Directory.Exists(folder))
{
Directory.CreateDirectory(folder);
}
return new System.IO.FileStream(imageFilePath, FileMode.Create);
}
Generate document preview from stream with custom stream releasing delegate
public static void GetPreview()
{
using (var stream = File.OpenRead("sample.pdf"))
{
using (Signature signature = new Signature("sample.pdf"))
{
// create preview options object
PreviewOptions previewOption = new PreviewOptions(GeneratePreview.CreatePageStream)
{
PreviewFormat = PreviewOptions.PreviewFormats.JPEG,
};
// generate preview
signature.GeneratePreview(previewOption);
}
}
}
private static Stream CreatePageStream(int pageNumber)
{
string imageFilePath = Path.Combine("GeneratePreviewFolder", "image-" + pageNumber.ToString() + ".jpg");
var folder = Path.GetDirectoryName(imageFilePath);
if(!Directory.Exists(folder))
{
Directory.CreateDirectory(folder);
}
return new System.IO.FileStream(imageFilePath, FileMode.Create);
}
private static void ReleasePageStream(int pageNumber, Stream pageStream)
{
pageStream.Dispose();
string imageFilePath = Path.Combine("GeneratePreviewFolder", "image-" + pageNumber.ToString() + ".jpg");
Console.WriteLine("Image file {0} is ready for preview", imageFilePath);
}
Advanced Usage Topics
To learn more about document eSign features, please refer to the advanced usage section.
More resources
GitHub Examples
You may easily run the code above and see the feature in action in our GitHub examples:
- GroupDocs.Signature for .NET examples, plugins, and showcase
- GroupDocs.Signature for Java examples, plugins, and showcase
- Document Signature for .NET MVC UI Example
- Document Signature for .NET App WebForms UI Example
- Document Signature for Java App Dropwizard UI Example
- Document Signature for Java Spring UI Example
Free Online App
Along with full-featured .NET library we provide simple, but powerful free Apps.
You are welcome to eSign PDF, Word, Excel, PowerPoint documents with free to use online GroupDocs Signature App.