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GetInformationAsync(string,bool,int,object) Method

Summary
Gets the image information from a disk file asynchronously.
Syntax
C#
VB
Objective-C
C++
public CodecsImageInfo GetInformationAsync( 
   string fileName, 
   bool totalPages, 
   int pageNumber, 
   object userState 
) 
Public Overloads Function GetInformationAsync( _ 
   ByVal fileName As String, _ 
   ByVal totalPages As Boolean, _ 
   ByVal pageNumber As Integer, _ 
   ByVal userState As Object _ 
) As CodecsImageInfo 
- (void)imageInformationForFileAsync:(NSString *)file  
                          totalPages:(BOOL)totalPages  
                          pageNumber:(NSInteger)pageNumber  
                          completion:(void (^)(LTCodecsImageInfo * __nullable info, NSError * __nullable error))completion 
public: 
CodecsImageInfo^ GetInformationAsync(  
   String^ fileName, 
   bool totalPages, 
   int pageNumber, 
   Object^ userState 
)  

Parameters

fileName
String containing the input file name to query.

totalPages
true to query the file for total number of pages; false, otherwise.

pageNumber
The page number to query. Pass 1 for the first page (default).

userState
A user-defined object that is passed to the method invoked when the asynchronous operation completes.

Return Value

A CodecsImageInfo object that contains the information about the specified image. See remarks about 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<CodecsImageInfo> GetInformationAsync(ILeadStream stream, bool totalPages, int pageNumber).

Specifying true for totalPages can cause the process to be slow for files with large number of pages.

The RasterCodecs class supports getting information on image files asynchronously using the GetInformationAsync methods. When calling any of these methods, the caller thread will not be blocked and the method will return instantly with an instance CodecsImageInfo that is in a loading status (CodecsImageInfo.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 getting the information about the file, the various properties of the CodecsImageInfo will be populated with the image file information and the CodecsImageInfo.IsLoading property will be set to false.

It is recommended that you do not poll for the CodecsImageInfo.IsLoading property to determine whether the image information has been collected. Instead, subscribe to the GetInformationAsyncCompleted event to get notification on when the GetInformationAsync operation is completed and whether any errors occurred.

The GetInformationAsyncCompleted event data will also contain the same object returned from GetInformationAsync so you do not have to keep the original object in your application. userState will be passed to the CodecsGetInformationAsyncCompletedEventArgs.UserState member of the GetInformationAsyncCompleted event data.

Example
C#
using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing; 
using Leadtools.ImageProcessing.Color; 
using Leadtools.Svg; 
 
 
public void GetInformationAsyncFileExample() 
{ 
	string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Image1.cmp"); 
 
	RasterCodecs codecs = new RasterCodecs(); 
 
	// Now get information about the file asynchronously 
	codecs.GetInformationAsyncCompleted += new EventHandler<CodecsGetInformationAsyncCompletedEventArgs>(GetInformationAsyncFileExample_GetInformationAsyncCompleted); 
	object imageInfoObject = codecs.GetInformationAsync(srcFileName, true, 1, null); 
 
	// Notice that the returned imageInfoObject is a CodecsImageInfo with IsLoading set to true at this point 
	// The IsLoading will be false (and hence, the object will be usable) when the GetInformationAsyncCompleted 
	// fires. 
} 
 
private void GetInformationAsyncFileExample_GetInformationAsyncCompleted(object sender, CodecsGetInformationAsyncCompletedEventArgs e) 
{ 
	if (e.Cancelled) 
	{ 
		Console.WriteLine("User canceled"); 
	} 
	else if (e.Error != null) 
	{ 
		Console.WriteLine("Error: " + e.Error.Message); 
	} 
	else 
	{ 
		// Get the image info 
		CodecsImageInfo info = e.Info; 
		Console.WriteLine("Image info obtainted asynchronously:\n{0}", info.ToString()); 
		info.Dispose(); 
	} 
 
	// Unsubscribe to the event and dispose the RasterCodecs object 
	RasterCodecs codecs = sender as RasterCodecs; 
	codecs.GetInformationAsyncCompleted -= new EventHandler<CodecsGetInformationAsyncCompletedEventArgs>(GetInformationAsyncFileExample_GetInformationAsyncCompleted); 
	codecs.Dispose(); 
} 
 
static class LEAD_VARS 
{ 
   public const string ImagesDir = @"C:\LEADTOOLS21\Resources\Images"; 
} 
Requirements

Target Platforms

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