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LoadPicture Event

Summary

Occurs when a picture object has been finished loading its source image.

Syntax
C#
VB
Java
Objective-C
C++
public event EventHandler<AnnLoadPictureEventArgs> LoadPicture 
Public Event LoadPicture As EventHandler(Of AnnLoadPictureEventArgs) 
@property (nonatomic,assign) id<LTAnnRenderingEngineDelegate> delegate; 
public void addLoadPictureEventListener(AnnLoadPictureEventListener listener) 
public void removeLoadPictureEventListener(AnnLoadPictureEventListener listener) 
public:  
   event EventHandler<AnnLoadPictureEventArgs^>^ LoadPicture 

Event Data

The event handler receives an argument of type AnnLoadPictureEventArgs containing data related to this event. The following AnnLoadPictureEventArgs properties provide information specific to this event.

PropertyDescription
AnnObject Gets the owner annotation object.

Remarks

AnnLoadPictureEventArgs In the LEADTOOLS Annotation framework, the source image in picture objects is not loaded till render time. For example, when you first render an annotation object that contains a picture, such as the AnnHotspotObject or AnnPointObject, the framework will load the image in AnnPicture.Source in the background. While the image is loading, the framework will use a placeholder rectangle to render the object position and size. When the image is fully loaded, the framework will fire the LoadPicture event and renders the new image instead of the placeholder.

LoadingPictureStroke and LoadingPictureFill are the objects to use for stroking and filling the placeholder rectangle. The default values are a white stroke on a black background.

The LoadPicture event contains data about the picture that finished loading such as the Picture object itself and the owner AnnObject. Also, the event data contains the Error property that will be populated if an error occurred.

Loading an image in the background is an efficient and easy way to start drawing an annotation object without waiting for all the resources to be available in the browser. This is especially true if the object contains a picture with a source URL on a server machine and takes a few seconds to download.

Example

This example will create a picture from a resource in a remote server and use it with a hotspot annotation object. It will then uses automation to start drawing the object as the image is being loaded.

C#
using LeadtoolsExamples.Common; 
using Leadtools.Annotations.Automation; 
using Leadtools.Annotations.Engine; 
using Leadtools.Annotations.Rendering; 
using Leadtools.Codecs; 
using Leadtools.Annotations.WinForms; 
 
public void AnnRenderingEngine_LoadPicture() 
{ 
   // get the current rendering engine 
   AnnRenderingEngine renderingEngine = _automation.AutomationControl.RenderingEngine; 
 
   // Change the default loading object placeholder to be a green border with semi-transparent background 
   AnnStroke stroke = AnnStroke.Create(AnnSolidColorBrush.Create("Green"), LeadLengthD.Create(1)); 
   AnnBrush fill = AnnSolidColorBrush.Create("rgba(0, 0, 0, 0.5)"); 
 
   renderingEngine.LoadingPictureStroke = stroke; 
   renderingEngine.LoadingPictureFill = fill; 
 
   // Hook to the LoadPicture event 
   renderingEngine.LoadPicture += renderingEngine_LoadPicture; 
 
   // Create a new AnnHotspotObject with a picture from a remote server 
   double inch = 720; 
   AnnHotspotObject hotspot = new AnnHotspotObject(); 
   // Add the object at location 1,1 inch with size 4,2 inches 
   hotspot.Rect = LeadRectD.Create(1 * inch, 1 * inch, 4 * inch, 2 * inch); 
   // Set its picture 
   AnnPicture picture = new AnnPicture("ms-appx:///Assets/Logo.png"); 
   hotspot.Picture = picture; 
 
   // Add it to the container 
   AnnContainer container = _automation.Container; 
   container.Children.Add(hotspot); 
 
   _automation.Invalidate(LeadRectD.Empty); 
} 
 
void renderingEngine_LoadPicture(object sender, AnnLoadPictureEventArgs e) 
{ 
   // Check if an error occurred 
   if (e.Error != null) 
   { 
      // Show info about the error 
      string str = e.Error.Message; 
      str += "\nSource: " + e.Picture.Source; 
      str += "\nOwner object: " + e.AnnObject.FriendlyName; 
      Debug.WriteLine(str); 
   } 
} 

Requirements

Target Platforms

Help Version 20.0.2019.3.11
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Leadtools.Annotations.Engine Assembly