LoadAsync(String,Int32,Object) Method

C#
Visual Basic
WinRT C#
Java
Objective-C
WinRT JavaScript
C++

public RasterImage LoadAsync( 
   string fileName,
   int pageNumber,
   object userState
)

'Declaration

Public Overloads Function LoadAsync( _
   ByVal fileName As String, _
   ByVal pageNumber As Integer, _
   ByVal userState As Object _
) As RasterImage

'Usage

Dim instance As RasterCodecs
Dim fileName As String
Dim pageNumber As Integer
Dim userState As Object
Dim value As RasterImage
 
value = instance.LoadAsync(fileName, pageNumber, userState)

public RasterImage LoadAsync( 
   string fileName,
   int pageNumber,
   object userState
)

- (void)loadFileAsync:(NSString *)file 
           pageNumber:(NSInteger)pageNumber 
           completion:(void (^)(LTRasterImage * __nullable image, NSError * __nullable error))completion

 function Leadtools.Codecs.RasterCodecs.LoadAsync(String,Int32,Object)( 
   fileName ,
   pageNumber ,
   userState 
)

public:
RasterImage^ LoadAsync( 
   String^ fileName,
   int pageNumber,
   Object^ userState
)

Parameters

fileName: A String containing the name of the image file to load.
pageNumber: The 1-based page number.
userState: A user-defined object that is passed to the method invoked when the asynchronous operation completes.

Return Value

The RasterImage object that this method loads. See remarks for the usage of this object.

The file can be in any supported image file format and bits per pixel, whether compressed or uncompressed.

This method will load a single page from a multi-page file. The resulting image will have the same bits/pixel and color order value of the image as it was stored in the file.

LEADTOOLS will attempt to load corrupted files so you can see at least a portion of the image. For these images, the load methods succeed, but LoadStatus will return an error code.

Use the CodecsLoadOptions class to set up other load option parameters before calling this method.

Support for 12 and 16-bit grayscale images is only available in the Document/Medical Imaging editions.

For supported formats, refer to Summary of All Supported Image File Formats.

LEADTOOLS loads all PDF files as Raster PDF uncompressed RasterImageFormat.RasPdf, regardless of the compression and color space used when saving the file.

The RasterCodecs class supports loading image files asynchronously using the LoadAsync methods. When calling any of these methods, the caller thread will not be blocked and the method will return instantly with an instance of RasterImage that is in a loading status (RasterImage.IsLoading set to true). You should not use the other properties of this object while the object is in loading status.

When the RasterCodecs object finishes loading the image, the various properties of the RasterImage will be populated with the image information and data and the RasterImage.IsLoading property will be set to false.

Do not poll the RasterImage.IsLoading property to determine whether the image has finished loading. Instead, subscribe to the LoadAsyncCompleted event to get notification when the LoadAsync operation has completed and whether any errors occurred.

The LoadAsyncCompleted event data will also contain the same object returned from LoadAsync so you do not have to keep the original object in your application.

This example will query the number of pages from a file and then load them.

C#
Visual Basic
WinRT C#
WinRT JavaScript
Silverlight C#
Silverlight VB

Copy Code

Imports Leadtools
Imports Leadtools.Codecs
Imports Leadtools.ImageProcessing
Imports Leadtools.ImageProcessing.Color
Imports Leadtools.Drawing
Imports Leadtools.Svg

Class LoadPagesFromFileAsyncTestData
   Public PageCount As Integer
   Public PageNumber As Integer
End Class
Private Shared Sub LoadPagesFromFileAsyncTest(fileName As String)
   ' Create a new RasterCodecs instance, we will dispose it when the images finish loading
   Dim rasterCodecs As New RasterCodecs()

   ' Create the data
   Dim data As New LoadPagesFromFileAsyncTestData()

   ' Get the number of pages
   data.PageCount = rasterCodecs.GetTotalPages(fileName)
   Console.WriteLine("Number of pages in the file is {0}", data.PageCount)

   ' Load all pages asynchrounsly
   data.PageNumber = 1

   ' Start with the first page, then load next when operation finishes
   AddHandler rasterCodecs.LoadAsyncCompleted, AddressOf rasterCodecs_LoadAsyncCompleted
   rasterCodecs.LoadAsync(fileName, data.PageNumber, data)
End Sub

Private Shared Sub rasterCodecs_LoadAsyncCompleted(sender As Object, e As CodecsLoadAsyncCompletedEventArgs)
   ' A page is loaded, show info
   Dim data As LoadPagesFromFileAsyncTestData = CType(e.UserState, LoadPagesFromFileAsyncTestData)
   Console.WriteLine("Page {0} loaded", data.PageNumber)

   ' If there is an error, show it
   If Not IsNothing(e.Error) Then
      Console.WriteLine("Error {0}", e.Error.Message)
   End If

   ' Dispose the image
   If Not IsNothing(e.Image) Then
      e.Image.Dispose()
   End If

   ' Get the raster codecs instance
   Dim rasterCodecs As RasterCodecs = CType(sender, RasterCodecs)

   If data.PageNumber < data.PageCount Then
      ' Load next
      Console.WriteLine("Load next")
      data.PageNumber = data.PageNumber + 1
      rasterCodecs.LoadAsync(e.FileName, data.PageNumber, data)
   Else
      ' Finished loading, clean up
      Console.WriteLine("Finished")
      RemoveHandler rasterCodecs.LoadAsyncCompleted, AddressOf rasterCodecs_LoadAsyncCompleted
      rasterCodecs.Dispose()
   End If
End Sub

using Leadtools;
using Leadtools.Codecs;
using Leadtools.ImageProcessing;
using Leadtools.ImageProcessing.Color;
using Leadtools.Svg;

class LoadPagesFromFileAsyncTestData
{
   public int PageCount;
   public int PageNumber;
}
private static void LoadPagesFromFileAsyncTest(string fileName)
{
   // Create a new RasterCodecs instance, we will dispose it when the images finish loading
   RasterCodecs rasterCodecs = new RasterCodecs();

   // Create the data
   LoadPagesFromFileAsyncTestData data = new LoadPagesFromFileAsyncTestData();

   // Get the number of pages
   data.PageCount = rasterCodecs.GetTotalPages(fileName);
   Console.WriteLine("Number of pages in the file is {0}", data.PageCount);

   // Load all pages asynchrounsly
   data.PageNumber = 1;

   // Start with the first page, then load next when operation finishes
   rasterCodecs.LoadAsyncCompleted += new EventHandler<CodecsLoadAsyncCompletedEventArgs>(rasterCodecs_LoadAsyncCompleted);
   rasterCodecs.LoadAsync(fileName, data.PageNumber, data);
}

private static void rasterCodecs_LoadAsyncCompleted(object sender, CodecsLoadAsyncCompletedEventArgs e)
{
   // A page is loaded, show info
   LoadPagesFromFileAsyncTestData data = e.UserState as LoadPagesFromFileAsyncTestData;
   Console.WriteLine("Page {0} loaded", data.PageNumber);

   // If there is an error, show it
   if (e.Error != null)
      Console.WriteLine("Error {0}", e.Error.Message);

   // Dispose the image
   if (e.Image != null)
      e.Image.Dispose();

   // Get the raster codecs instance
   RasterCodecs rasterCodecs = sender as RasterCodecs;

   if (data.PageNumber < data.PageCount)
   {
      // Load next
      Console.WriteLine("Load next");
      data.PageNumber++;
      rasterCodecs.LoadAsync(e.FileName, data.PageNumber, data);
   }
   else
   {
      // Finished loading, clean up
      Console.WriteLine("Finished");
      rasterCodecs.LoadAsyncCompleted -= new EventHandler<CodecsLoadAsyncCompletedEventArgs>(rasterCodecs_LoadAsyncCompleted);
      rasterCodecs.Dispose();
   }
}

Target Platforms

Reference

RasterCodecs Class
RasterCodecs Members
Overload List
Loading and Saving Images
Loading and Saving Large TIFF / BigTIFF Files
Speeding Up 1-Bit Documents
Fast File Info