问题
I have a Silverlight control containing an image. I want the user to be able to drag the image out of the Silverlight application and drop it anywhere they would be able to drop an image. For example, to the Desktop or to a PowerPoint slide or Word document. Everything that I have read thus far says it cannot be done but I find that hard to believe. I'm very new to Silverlight and RIA development so any help would be much appreciated.
Below is the code sample in my WinForm Form but the drag never starts.
string[] aString = { imagePath };
DataObject data = new DataObject(DataFormats.FileDrop, aString);
data.SetData(DataFormats.StringFormat, imagePath);
DoDragDrop(data, DragDropEffects.Copy);
回答1:
Well the trouble is that a drag operation in Silverlight doesn't have simple access to anything outside the browser (by design). Depending on the user's settings you even have to get explicit permission for clipboard operations and sandboxed temporary file storage. This really sounds like a task better suited to a WPF application (perhaps with web deployment?) or some other desktop application technology.
However, that being said here are some things you could try/consider:
- Silverlight/Javascript/ActiveX combination hosted in Internet Explorer
- Silverlight 5 "Out of Brower" & P/Invoke (I heard P/Invoke will be supported when Silverlight 5 comes out)
- Silverlight connecting to a web service running on the same computer (crazy, but you didn't ask for "not crazy", you asked for possible)
I am not very familiar with drag and drop in the Win32 API so it would take a lot of research and experimentation before I could confirm that this was even possible (and I can already tell you it isn't practical).
Edit: Based on the extra information you provided about the question I suspect it is possible to do what you are attempting. First, are you using WPF or WinForms? I assume WPF but one of your comments says WinForms. I wasn't very familiar with WPF drag/drop operations, but having looked into it, I think your code is on the right path. I created a WPF application and initiated a drag during a KeyDown event. This meant that the mouse button was not necessarily pressed. If I initiated the DragDrop while the button was down it worked. If I initiated while the mouse button wasn't down, I had to push the mouse button down and the drag operation would start (this was unexpected since I assumed the mouse would have to already be down). If I pressed the mouse down outside the application, then gave the WPF app focus (ALT+Tab), then initiated the DragDrop while the mouse button was still down, it didn't work. I got a reference to the MouseDevice and checked the LeftButton property, and the state was showing as "Released" even though the button was still being held down. It seems the key here is the way drag/drop interacts with internal mouse state. You might have to find a way to set the mouse state (maybe with the UI Automation API?). At this point it should be painfully obvious that this whole thing is a hack (even though it is probably possible to get it to work somehow).
回答2:
The solution we came up with was as follows. The RIA i.e. Silverlight sends a message to our Desktop application WinForms with the path of the image to drag along with the bounding rectangle in screen coordinates that we want to start the drag from. The Desktop code creates and places a Panel over the area that we want to drag from. This panel is where we use DoDragDrop to initiate the native drag when the user left clicks. Since this panel is placed outside and above the silverlight control, everything works perfect. Sandbox defeated.
回答3:
I have been working on some Silverlight apps for the past few months and fully investigated your exact requirements only to find it was not possible. I believe you can drag from the file system, from Silverlight control to control, but not to the file system.
Does Silverlight 4 support drag and drop from app to desktop?
http://msdn.microsoft.com/en-us/library/dd772166%28v=vs.95%29.aspx
来源：https://stackoverflow.com/questions/7168357/i-want-to-drag-an-image-from-a-silverlight-uielement-and-drop-it-on-the-users-de