print barcode in crystal report vb.net Event in Visual Basic .NET

Maker Quick Response Code in Visual Basic .NET Event

Fires when the image source is downloaded and decoded with no failure. You can use this event to determine the size of an image before rendering it. If the imagedecode fails for any reason, this event does not fire. Once this event fires, the PixelHeight and PixelWidth properties are guaranteed to be valid.

DownloadProgress Reports the progress of the image download. The EventArgs class is DownloadProgressEventArgs and contains a Progress property that reports either a 0 (indicating that the image is possibly in the process of downloading) or a 1 (indicating that the image has finished downloading). ImageFailed Fires when the image cannot be downloaded or the image format is invalid. The event handler is passed an ExceptionRoutedEventArgs instance, which has ErrorException (the thrown Exception) and ErrorMessage properties.

If you don t specify a width or height for an image, it will display without any modifications to the image s natural width and height. The Image control has a property named Stretch (it is also a

dependency property) that controls how an image conforms to a container. The Stretch property can have one of the following four Stretch type enum values: None: The image maintains its original size. Fill: The image completely fills the output area, both vertically and horizontally. The image might appear distorted because the aspect ratio is not preserved. Uniform: The image fills the output area, both vertically and horizontally, but maintains its aspect ratio. This is the default value. UniformToFill: The image is scaled to completely fill the output area, but its aspect ratio is maintained. You can see the result of the various Stretch values in Figure 4-1. Reading left to right and top to bottom, Stretch takes on the values None, Fill, Uniform, and UniformToFill.

Figure 4-1. A visual demonstration of each Stretch value The image is 100 80, so we can see how the image is treated in a 200 200 square area. The bounding box for the image is defined on the Image control. <Image Source="target.png" Stretch="None" Height="200" Width="200"/> The image is left completely unaltered when Stretch is set to None it maintains its size of 100 80. When Stretch is set to Fill, the image appears distorted because it is taller than it is wide. For Uniform, the image now almost doubles in size. It doesn t quite fill its bounding box because it is maintaining its aspect ratio. Finally, UniformToFill is similar to Uniform but the image is scaled to the full size of the

bounding box. While this specific image can still be completely seen, it is possible that the image will be cut off either horizontally or vertically in order to simultaneously fill its bounding box and maintain its aspect ratio. Let s take a closer look at these capabilities by implementing a sample application image viewer. In this sample application, a list box will contain several ListBoxItem instances, each containing an image scaled down by setting its width/height (we re using only one source image, but for a serious image browser, you might want to store thumbnails separately due to image file size). When a specific image is clicked, the image is shown at full size. The resulting user interface is shown in Figure 4-2.

Figure 4-2. User interface for an image viewer using a list box Here we first define the Grid control with two columns and one row, as shown here: <Grid x:Name="LayoutRoot" Background="White"> <Grid.ColumnDefinitions> <ColumnDefinition Width="100"/> <ColumnDefinition Width="*"/> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition/>

</Grid.RowDefinitions> </Grid> Now I created a Sample folder under the ImageViewer project and added four JPEG images from the Sample Pictures folder that comes as part of Windows 7. Rename them 001.jpg to 004.jpg and set each image BuildAction property to Resource. Go back to the XAML code and add a list box to the first column of the Grid (using Grid.Column) and add these four images as ListBoxItems to the list box. Here notice that the SelectionChanged event is integrated with code-behind. <ListBox x:Name="thumbnailList" Width="100" Grid.Column="0" SelectionChanged="thumbnailList_SelectionChanged"> <ListBox.Items> <ListBoxItem> <Image Source="Sample/001.jpg" Width="75" Height="50" </ListBoxItem> <ListBoxItem> <Image Source="Sample/002.jpg" Width="75" Height="50" </ListBoxItem> <ListBoxItem> <Image Source="Sample/003.jpg" Width="75" Height="50" </ListBoxItem> <ListBoxItem> <Image Source="Sample/004.jpg" Width="75" Height="50" </ListBoxItem> </ListBox.Items> </ListBox>