Leadtools.Codecs Namespace > RasterCodecs Class > LoadAsync Method : LoadAsync(Uri,LeadRect,Object) Method |
'Declaration Public Overloads Function LoadAsync( _ ByVal uri As Uri, _ ByVal tile As LeadRect, _ ByVal userState As Object _ ) As RasterImage
'Usage Dim instance As RasterCodecs Dim uri As Uri Dim tile As LeadRect Dim userState As Object Dim value As RasterImage value = instance.LoadAsync(uri, tile, userState)
This method loads a section of an image file (any format). The section begins is defined by tile rectangle.
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.
LEADTOOLS supports the following URI schemes:Scheme | Description |
---|---|
System.Uri.UriSchemeFile | Specifies that the URI is a disk file in local machine or universal naming convention (UNC) path. |
System.Uri.UriSchemeHttp | Specifies that the URI is accessed through the Hypertext Transfer Protocol (HTTP). |
System.Uri.UriSchemeHttps | Specifies that the URI is accessed through the Secure Hypertext Transfer Protocol (HTTPS). |
System.Uri.UriSchemeFtp | Specifies that the URI is accessed through the File Transfer Protocol (FTP). |
If uri points to a resource in a System.Uri.UriSchemeHttp, System.Uri.UriSchemeHttps or System.Uri.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 thread will not be blocked and the method will return instantly with an instance of Leadtools.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 Leadtools.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(String,LeadRect,Int32,CodecsLoadByteOrder,Int32,Int32,Object) 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.
The CodecsLoadOptions.AllPages property controls whether RasterCodecs will try to load all pages or just the first page if the image data contains multiple pages.
Imports Leadtools Imports Leadtools.Codecs Imports Leadtools.ImageProcessing Imports Leadtools.ImageProcessing.Color Imports Leadtools.Drawing Public Sub LoadAsyncUrl2Example() Dim codecs As New RasterCodecs() Dim srcFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp") Dim uri As New Uri(srcFileName) ' Load a random tile from the image asynchronously Dim tileRect As New LeadRect(100, 50, 200, 150) AddHandler codecs.LoadAsyncCompleted, AddressOf LoadAsyncUrl2Example_LoadAsyncCompleted Dim rasterImageObject As Object = codecs.LoadAsync(uri, tileRect, Nothing) ' 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. End Sub Private Sub LoadAsyncUrl2Example_LoadAsyncCompleted(ByVal sender As Object, ByVal e As CodecsLoadAsyncCompletedEventArgs) If e.Cancelled Then Console.WriteLine("User canceled") ElseIf Not IsNothing(e.Error) Then Console.WriteLine("Error: " + e.Error.Message) Else ' Everything is OK, get the image Dim image As RasterImage = e.Image Console.WriteLine("Image at {0} loaded OK, size: {1} by {2}, order: {3}, bits/pixel: {4}", e.Uri, image.Width, image.Height, image.Order, image.BitsPerPixel) image.Dispose() End If ' Unsubscribe to the event and dispose the RasterCodecs object Dim codecs As RasterCodecs = DirectCast(sender, RasterCodecs) RemoveHandler codecs.LoadAsyncCompleted, AddressOf LoadAsyncUrl2Example_LoadAsyncCompleted codecs.Dispose() End Sub Public NotInheritable Class LEAD_VARS Public Const ImagesDir As String = "C:\Users\Public\Documents\LEADTOOLS Images" End Class
using Leadtools; using Leadtools.Codecs; using Leadtools.ImageProcessing; using Leadtools.ImageProcessing.Color; public void LoadAsyncUrl2Example() { RasterCodecs codecs = new RasterCodecs(); string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp"); Uri uri = new Uri(srcFileName); // Load a random tile from the image asynchronously LeadRect tileRect = new LeadRect(100, 50, 200, 150); codecs.LoadAsyncCompleted += new EventHandler<CodecsLoadAsyncCompletedEventArgs>(LoadAsyncUrl2Example_LoadAsyncCompleted); object rasterImageObject = codecs.LoadAsync(uri, tileRect, 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 LoadAsyncUrl2Example_LoadAsyncCompleted(object sender, CodecsLoadAsyncCompletedEventArgs e) { if (e.Cancelled) { Console.WriteLine("User canceled"); } else if (e.Error != null) { Console.WriteLine("Error: " + e.Error.Message); } else { // Everything is OK, get the image RasterImage image = e.Image; Console.WriteLine("Image at {0} loaded OK, size: {1} by {2}, order: {3}, bits/pixel: {4}", e.Uri, image.Width, image.Height, image.Order, image.BitsPerPixel); image.Dispose(); } // Unsubscribe to the event and dispose the RasterCodecs object RasterCodecs codecs = sender as RasterCodecs; codecs.LoadAsyncCompleted -= new EventHandler<CodecsLoadAsyncCompletedEventArgs>(LoadAsyncUrl2Example_LoadAsyncCompleted); codecs.Dispose(); } static class LEAD_VARS { public const string ImagesDir = @"C:\Users\Public\Documents\LEADTOOLS Images"; }