9: Working with Data in Silverlight in Visual Studio .NET

Encoder QR-Code in Visual Studio .NET 9: Working with Data in Silverlight

isoStore = IsolatedStorageFileGetUserStoreForApplication()) { using (IsolatedStorageFileStream isoStream = new IsolatedStorageFileStream("UserCredentialstxt", FileModeCreate, isoStore)) { using (StreamWriter writer = new StreamWriter(isoStream)) { writerWrite(userUserName + "|" + userPasswordHash); } } } }

The preceding code snippet illustrates using the IsolatedStorageFile class and the IsolatedStorageFileStream class to work with Isolated Storage The following code snippet illustrates using the same classes to determine if the UserCredentialstxt file exists in Isolated Storage If it does exist, the contents of the file are read

// determine if the user's credentials exist in isolated storage using (IsolatedStorageFile isoStore = IsolatedStorageFileGetUserStore ForApplication()) { using (IsolatedStorageFileStream isoStream = new IsolatedStorageFileStream("UserCredentialstxt", FileModeOpen, isoStore)) { using (StreamReader reader = new StreamReader(isoStream)) { // read the credentials string[] sb = readerReadLine()Split('|'); // do we have credentials if (sbLength > 0) { // if the credentials exist, parse them out and authenticate them userUserName = sb[0]; userPassword = sb[1]; // authenticate svcAuthenticateUserAsync(userUserName, userPassword); } } } }

The preceding section mentioned that Silverlight, on its own accord, cannot access the user s local file system This behavior is a security precaution to prevent malicious scripts from taking advantage of a user s machine through the Silverlight plug-in Silverlight 3 introduces a Save As File dialog that can be used to save files to the user s local file system Silverlight includes a companion Open File dialog that can be used to, not surprisingly, open files from the user s local file system Upon first glance, this may seem like a contradiction of the IO interaction security precaution taken with isolated storage However, the Save As File dialog and the Open File dialog can be displayed only through user interaction, such as the user clicking a button to initiate the save/open file process Additionally, the Save As File dialog and the Open File dialog do not expose any information about the user s file system to a Silverlight application but simply provide a stream for writing data to and reading data from based on the user s selection The Save As File dialog and the Open File dialog are not utilized in Silverlight XAML but are controlled programmatically In the following markup, a simple form displays text contents in a Textbox and displays two buttons one for opening a file and one for saving a file:

<UserControl x:Class="L0905Page" xmlns="http://schemasmicrosoftcom/winfx/2006/xaml/presentation" xmlns:x="http://schemasmicrosoftcom/winfx/2006/xaml" xmlns:d="http://schemasmicrosoftcom/expression/blend/2008" xmlns:mc="http://schemasopenxmlformatsorg/markupcompatibility/2006" mc:Ignorable="d" d:DesignWidth="400" Height="88"> <Grid x:Name="LayoutRoot" Background="White" Height="88" VerticalAlignment="Top"> <ScrollViewer Margin="8,8,8,33" d:LayoutOverrides="VerticalAlignment"> <TextBox x:Name="txtData" Height="Auto" Width="Auto" Text="" TextWrapping="Wrap"/> </ScrollViewer> <Button x:Name="btnOpen" Height="Auto" Margin="0,0,91,7" VerticalAlignment="Bottom" Width="91" Content="open" HorizontalAlignment="Right" RenderTransformOrigin="0486,-0045" Click="btnOpen_Click" d:LayoutOverrides="VerticalAlignment" /> <Button x:Name="btnSave" Height="Auto" Margin="0,0,8,7" VerticalAlignment="Bottom" Content="save" Width="79" HorizontalAlignment="Right" Click="btnSave_Click" d:LayoutOverrides="VerticalAlignment" /> </Grid> </UserControl>

Figure 9-3

The code used to open a file from the file system is shown in the following code listing The Silverlight form is shown in Figure 9-3

private void btnOpen_Click(object sender, RoutedEventArgs e) { OpenFileDialog dialog = new OpenFileDialog() { Filter = "Text Files|*txt|All Files|**", FilterIndex = 1 }; if (dialogShowDialog() == true) { FileInfo openFile = dialogFile; StreamReader reader = openFileOpenText(); txtDataText = readerReadToEnd(); readerClose(); } }

Finally, the code used to save the contents of the form Textbox to a local text file is shown here:

private void btnSave_Click(object sender, RoutedEventArgs e) { SaveFileDialog dialog = new SaveFileDialog() { DefaultExt = "txt", Filter = "Text Files|*txt|All Files|**", FilterIndex = 1 }; if (dialogShowDialog() == true) {

using (Stream saveStream = dialogOpenFile()) { // write the data byte[] data = EncodingUnicodeGetBytes (txtDataText); saveStreamWrite(data, 0, dataLength); saveStreamClose(); } } }

Silverlight 3 provides multiple methods for binding user interface controls and components directly to business objects and data sources This is known as data binding Under the data binding umbrella, the user interface component is called the target, whereas the data source is called the source A key user interface control used to display tabular data to users, the DataGrid control, was illustrated in 8 The DataGrid control can be easily data bound by assigning the data source to the ItemsSource property of the DataGrid control A few other user interface controls may also be easily and directly data bound to a source, including the Listbox control and the Combobox control