DRAG AND DROP SYSTEM DESIGNER THAT GENERATE CODES CODE

Here's the complete method:Ĭopy Code public delegate void AssignImageDlgt() The rest of the OnDragEnter method handles this logic, in addition to determining whether we set the drag effect to Copy. loading the image into the application is a time consuming process, and I don't want to bog the application's main thread down by loading it.what if the image being dragged is already the same image the application is displaying?.This is a good example that illustrates that sometimes you'll have to manage the data intelligently. Now that we have the filename, what do we do with it? In my application, I'd like to display a small image to give the user some feedback, showing the picture about to be dropped onto the application. If all is well, the method returns true, indicating success, along with the filename. Once I've done all this verification, I can get the filename, extract the extension, and confirm that it's either '.jpg', '.bmp', or '.png'. Verify that there is only one datum being dropped (rather than a collection of filenames) and, while probably overkill, I want to verify that the data type of this one and only one entry is a string. The object returned is actually an Array, as evident in the watch window: We see that 'FileName' is one of the acceptable formats, so I'm going to request that data in the FileName format. When dropping an image, there are several formats that the data supports, which can be inspected in the debugger: Second, I get the data based on the filename. bmp') )įirst, I test whether the source allows copying of the data. String ext=Path.GetExtension(filename).ToLower() If ( (data.Length = 1) & (data.GetValue( 0) is String) ) If ( (e.AllowedEffect & DragDropEffects.Copy) = DragDropEffects.Copy)Īrray data=((IDataObject)e.Data).GetData( ' FileName') as Array As a result, the OnDragEnter method starts like this:Ĭopy Code protected bool GetFilename( out string filename, DragEventArgs e) is the data in a format that my application accepts?Īnd in particular, the application accepts images dragged from Explorer, so I'm interested in the filename.can the object be copied into my application?.

In my example, I'm interested in two things: KeyState - can be used to inspect the state of the SHIFT, CTRL, and ALT keys as well as mouse buttons.Effect - the target effect that we want to set for this object.Data - The IDataObject that actually contains the data in which we are interested.What we're primarily interested in is whether the source allows copying or moving. AllowedEffect - The operations that are allowed by the source of the drag event.The DragEventArgs contains several properties that we are interested in:

set the Effect property to indicate whether the item will be copied or moved to the control.

perform any initialization you may need to handle the data.

inspect the DragEventArgs to see the DataObject being dragged onto your control is something you can accept.

This is simple enough-this event fires when the mouse enters a control in which d&d is enabled. Since we're adding d&d capability to the form, we can use the designer to add our methods for the four events we're almost always interested in: The next step is to wire-up the d&d events (note that the PictureBox control doesn't show these events either in the designer, but yes, they are there and you can use them). In any case, since the demonstration application doesn't do anything else besides display an image, it makes sense in this case to enable d&d for the form rather than just the PictureBox. Yet, this doesn't mean that you can't manually assign this property! It seems like the PictureBox is the only control that doesn't expose this property, for no reason that I found. You won't be able to do drag and drop operations if this is missing (in fact, the program will display an error message if you try to run it-not by the program's doing, but by. The very first step is to ensure that your Main method is designated with the attribute. I've decided to illustrate d&d with a simple, single image viewer capable of viewing JPG, BMP, and PNG files. While simple, there are some things that I discovered when writing a little demonstration program, so I decided to write a beginner's tutorial on d&d.

DRAG AND DROP SYSTEM DESIGNER THAT GENERATE CODES HOW TO

Amazingly, I couldn't find one-all the examples I found seemed to deal with tree controls or didn't deal specifically with how to use d&d. I'm working on something now where I'd like to use that feature, and so I went searching for a simple example of how d&d works. Believe it or not, I've never written an application that's needed to use drag & drop.

Drag and drop system designer that generate codes