print barcode labels in vb.net Figure 10-12. Opening Notepad from Silverlight in C#

Creation PDF417 in C# Figure 10-12. Opening Notepad from Silverlight

A feature that users have grown very accustomed to in desktop applications is the ability to drag files directly onto the application and have some action take place. With web applications, in contrast, you ve always been restricted to browse functionality, which is not efficient or intuitive to users. Silverlight 4, however, supports the ability to drag files directly onto a Silverlight application. Currently this is limited to files, but you can see from the API that future releases of Silverlight will most likely support additional types. To enable drop functionality in your application, you need only enable one property on your UI element, AllowDrop. If you set AllowDrop to true on your element, your application can immediately access the drop target functionality. Once AllowDrop has been set, you have a number of events that will allow you to work with file(s) dropped onto your application. The DragEnter, DragLeave and DragOver events are fired during the drag process, but the primary event we are concerned with is the Drop event that occurs when a file is actually dropped onto our control.

The Drop event occurs when a file is dropped onto a control with AllowDrop enabled. This is the primary event that is used in enabling Silverlight as a drop target. From within the Drop event you can get information about the file list from the DropEventArgs.Data property. Let s get a closer look at enabling file drop in a Silverlight application by running through an example.

In this example, we ll create a simple Silverlight application that contains a TextBlock. We will then enable the application as a drop target and when a file is dropped, if it is a text document with extension *.txt, we will display the contents of the file in the TextBlock control. Let s get started. 1. Create a new Silverlight application in Visual Studio 2010. Name it SilverlightDropTarget and allow Visual Studio to create an ASP.NET web application called SilverlightDropTarget.Web to host your application. When the project is created, you should be looking at the MainPage.xaml file. First, set the AllowDrop property for the Grid to True. Then, within the LayoutRoot Grid of the Silverlight page, add a TextBlock named FileContents, and set the Margin to 10 and the TextWrapping property to Wrap. <Grid AllowDrop="True" x:Name="LayoutRoot" Background="White"> <TextBlock Margin="10" TextWrapping="Wrap" Name="FileContents" /> </Grid> 3. Now turn your attention to the code behind, MainPage.xaml.cs. First add a using reference to the System.IO namespace, then wire up the Drop event in the constructor.

public MainPage() { InitializeComponent(); LayoutRoot.Drop += new DragEventHandler(LayoutRoot_Drop); } 4. Next, in the LayoutRoot_Drop event, we ll start to work with the dropped file(s). First, we ll make certain that the data dropped on the application is not null. Next, we ll create an IDataObject set to the DragEventArgs.Data property passed into the event. We can then get the collection of files dropped using the GetData method. void LayoutRoot_Drop(object sender, DragEventArgs e) { if (e.Data != null) { IDataObject obj = e.Data; FileInfo[] files = obj.GetData(DataFormats.FileDrop) as FileInfo[]; } 5. }

Once we have a collection of files, we can create a foreach statement to step through each file within our collection. For each instance, we will inspect the file extension. If the extension is .txt, we will open the file using a StreamReader and read the contents of the file. Once we have read the contents, we will set that to the Text property of the FileContents TextBlock. void LayoutRoot_Drop(object sender, DragEventArgs e) { if (e.Data != null) { IDataObject obj = e.Data; FileInfo[] files = obj.GetData(DataFormats.FileDrop) as FileInfo[]; foreach (FileInfo file in files) { if (file.Extension.Equals(".txt")) { using (Stream stream = file.OpenRead()) { using (StreamReader reader = new StreamReader(stream)) { FileContents.Text = reader.ReadToEnd(); } } } } } }