LoadAsync(Uri,int,object) Method

Summary

Loads the specified page from an image URL using default options asynchronously.

Syntax

C++/CLI

Python

public RasterImage LoadAsync( 
   Uri uri, 
   int pageNumber, 
   object userState 
)

public: 
RasterImage^ LoadAsync(  
   Uri^ uri, 
   int pageNumber, 
   Object^ userState 
)

def LoadAsync(self,uri,pageNumber,userState):

Parameters

uri
The Uri containing the input image data.

pageNumber
1-based page number to load.

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.

Remarks

NOTE: This topic is part of RasterCodecs Async support using the .NET System.ComponentMode.AsyncOperation model. For .NET async/await, use Task<RasterImage> LoadAsync(ILeadStream stream, int pageNumber).

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 multipage 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 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.

LEADTOOLS supports the following URI schemes:

Scheme	Description
UriSchemeFile	Specifies that the URI is a disk file in local machine or universal naming convention (UNC) path.
UriSchemeHttp	Specifies that the URI is accessed through the Hypertext Transfer Protocol (HTTP).
UriSchemeHttps	Specifies that the URI is accessed through the Secure Hypertext Transfer Protocol (HTTPS).
UriSchemeFtp	Specifies that the URI is accessed through the File Transfer Protocol (FTP).

If uri points to a resource in a UriSchemeHttp, UriSchemeHttps or UriSchemeFtp, then this RasterCodecs will attempt to download image data in an iterative fashion by creating a temporary buffer. The size of this buffer can be determined and changed by setting up the UriOperationBufferSize prior to calling this method.

For authenticity and proxy settings, refer to UriOperationCredentials and UriOperationProxy.

The RasterCodecs class supports loading image files asynchronously using the LoadAsync methods. When calling any of these methods, the caller's 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.

Example

using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing; 
using Leadtools.ImageProcessing.Color; 
using Leadtools.Svg; 
 
 
public void LoadAsyncCompletedExample() 
{ 
   string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp"); 
   Uri uri = new Uri(srcFileName); 
 
   RasterCodecs codecs = new RasterCodecs(); 
 
   // Now load the image asynchronously 
   codecs.LoadAsyncCompleted += new EventHandler<CodecsLoadAsyncCompletedEventArgs>(LoadAsyncCompletedExample_LoadAsyncCompleted); 
   object rasterImageObject = codecs.LoadAsync(uri, null); 
 
   // Notice that the returned rasterImageObject is a RasterImage with IsLoading set to true at this point 
   // The IsLoading will be false (and hence, the object will be usable) when the LoadAsyncCompleteted 
   // fires. 
} 
 
private void LoadAsyncCompletedExample_LoadAsyncCompleted(object sender, CodecsLoadAsyncCompletedEventArgs e) 
{ 
   if (e.Cancelled) 
   { 
      Debug.WriteLine("User canceled"); 
   } 
   else if (e.Error != null) 
   { 
      Debug.WriteLine("Error: " + e.Error.Message); 
   } 
   else 
   { 
      // Everything is OK, get the image 
      RasterImage image = e.Image; 
      Debug.WriteLine("Image at {0} loaded OK, size: {1} by {2}", e.Uri, image.Width, image.Height); 
      image.Dispose(); 
   } 
 
   // Unsubscribe to the event and dispose the RasterCodecs object 
   RasterCodecs codecs = sender as RasterCodecs; 
   codecs.LoadAsyncCompleted -= new EventHandler<CodecsLoadAsyncCompletedEventArgs>(LoadAsyncCompletedExample_LoadAsyncCompleted); 
   codecs.Dispose(); 
} 
 
static class LEAD_VARS 
{ 
   public const string ImagesDir = @"C:\LEADTOOLS22\Resources\Images"; 
}

Requirements

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

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