Silverlight 4: Bye bye ControlParameter

If you've been using Silverlight 4 and some of its ria stuff, you may have noticed that the ControlParameter has gone missing. Actually it has gone for good - and that's a good thing.

ControlParameter was a misfit, why? Look at the following (old) code:

<riaData:ControlParameter ParameterName="title"
                             ControlName="filterTextBox"
                             PropertyName="Text" />

Now there's no databinding, and that most certainly isn't the (new) .NET way. Check out below how it should look now, with Silverlight 4. Here we doe some data filtering with DomainDataSource.FilterDescriptor.

<riaControls:DomainDataSource Name="ExampleSource" QueryName="GetExampleQuery" AutoLoad="True">
<riaControls:DomainDataSource.FilterDescriptors>
<riaControls:FilterDescriptor PropertyPath="title"
Operator="Contains" Value="{Binding Text, ElementName=filterTextBox}">
</riaControls:FilterDescriptor>
</riaControls:DomainDataSource.FilterDescriptors>
<riaControls:DomainDataSource.DomainContext>
<domain:ExampleDataContext />
</riaControls:DomainDataSource.DomainContext>
</riaControls:DomainDataSource>

See, everything is well now. :-)

Silverlight 4: Drag and drop from desktop or image

Ok, Silverlight 4 is here and everyone's very happy and excited (well.. I think it's just more fun now to use Silverlight - especially with the nice toolkit, which can be found on codeplex). Yesterday I tried one of the new features and wow, it was pretty easy to implement drag and drop for Silverlight 4 applications.

So let's say you got a Listbox, like the following one

<ListBox x:Name="myListBox" />

Now you have to add e few things:

• Allow Drop with AllowTrop="True"
• An eventhandler for the Drop event
• And finally if you want eventhandlers for DragEnter and DragLeave

The whole thing should look like the following

<ListBox Name="myListBox" 
         AllowDrop="True" 
         Drop="myListBox_Drop" 
         DragEnter="myListBox_DragEnter" 
         DragLeave="myListBox_DragLeave" />

Lets talk about the "Drop" event for a moment. Drop supplies the event handler with the arguments from DragEventArgs: Take a look at it on MSDN. Here's how I handle the event

private void myListBox_Drop(object sender, DragEventArgs e)
{
 FileInfo[] droppedFiles = e.Data.GetData(DataFormats.FileDrop) as FileInfo[];

 for (int i = 0; i < droppedFiles.Length; i++)
 {
  this.myListBox.Items.Add(droppedFiles[i].Name);
                /* you have to access the data in the listbox via droppedFiles[i].OpenRead()
                   things like File.OpenRead(droppedFiles[i].FullName) won't work because
                   of the Silverlight 4 security model */
 }

 e.Handled = true;
}

Additionally you can use the DragEnter and DragLeave event to alert the user, that dragged files can be dropped on the object - just change the background colour or something like that (a border is quite nice as well).