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Clipboard handling with .NETBy Nishant SivakumarAn introduction to using the clipboard |
C#.NET 1.0, Win2K, WinXP, Dev
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The clipboard is where your data is stored when you copy or cut some text or an
image or a file or a folder. The clipboard is common across processes, which
means we can use the clipboard as a mechanism to transfer data between two
processes. Win32 gave us a Clipboard API with functions like OpenClipboard and
GetClipboardData which most of you might be familiar with. In .NET Microsoft
has encapsulated the functionality of most of these functions into some
classes. The most prominent of these classes is a class which has
been named aptly as Clipboard. It's a very simple class with just
two functions. In this article, we'll see how to copy/paste text, images
and also how to maintain clipboard data in multiple formats.
I'd like to thank James Johnson for his amazing help while I was fiddling with the clipboard. I didn't have a reference book to help me, but that didn't matter much as James more than made up for it. Poor Mike Dunn had to suffer some .NET talk when he walked into Bob's HungOut just as I was discussing an issue with James. Anyway let's get on with things now.
The Clipboard class has a SetDataObject
function which is used to insert clipboard data. It takes an Object as
argument in the single argument overload. In the other overload it takes
both an Object and a bool variable, which we can set
to true if we want the clipboard to persist even
after our application has exited. In our example program we'll use the
second overload as that seems to be the more common situation, where we
would want other programs to access what we have copied onto the
clipboard.
Clipboard.SetDataObject(textBox1.Text,true);
The Clipboard class also has a
GetDataObject function which returns an IDataObject.
The IDataObject interface has a function called
GetDataPresent which we use to determine if the
IDataObject has data of a specific format. We can
use the static fields of the DataFormats class to
verify that the format we expect is indeed available in the
IDataObject. If GetDataPresent returns
true, we can then use the GetData
function to retrieve the data format that we are expecting.
if(Clipboard.GetDataObject().GetDataPresent(DataFormats.Text))
textBox1.Text = Clipboard.GetDataObject().GetData(DataFormats.Text).ToString();
else
textBox1.Text = "The clipboad does not contain any text";
Observe how I have copied some text from Notepad and pasted it into our sample program. You can also copy text from our program and paste it into Notepad. And I hope you like my XP theme and colors as well.
This is exactly the same as in copying and pasting text except that
we use the DataFormats.Bitmap
format instead of DataFormats.Text
Clipboard.SetDataObject(pictureBox1.Image,true);
if(Clipboard.GetDataObject().GetDataPresent(DataFormats.Bitmap))
pictureBox1.Image = (Bitmap)Clipboard.GetDataObject().GetData(DataFormats.Bitmap);
I have copied from Paint Brush into our sample program. You can then
copy something else using Paint Brush, come back to our program, copy
the image and paste back into Paint Brush. The image has stretched a bit
because I have set the SizeMode property of
the Picture control to StretchImage.
There are situations where you are not sure what kind of data the target application of a copy/paste cycle is expecting in the clipboard. In such cases we can maintain multiple data formats in the clipboard, so that the target application can retrieve the data format it's expecting. In our sample, we'll copy both the text in the edit box as well as the image in the picture control into the clipboard. Now you can open Notepad and paste into it the text as well as open Paint Brush and paste into it the bitmap. I have provided a [Paste Both] button for ease of demonstration. Just run a second instance of the sample program and we can paste both the text and the image into the respective controls.
We make use of the DataObject class which
implements the IDataObject interface. We call the
SetData function twice, each time passing in a
different format data. We use the following override of the function :-
[ClassInterface(ClassInterfaceType.None)]
public virtual void SetData(
string format, //This indicates what type of data this is going to be
bool autoConvert, //Set this true to allow automatic data format conversions
object data //The actual data [which is in the format specified above]
);
The code is very straightforward. We create a DataObject
object, use SetData twice, once with the text and
then with the image, then we add this DataObject to
the clipboard.
DataObject m_data = new DataObject();
m_data.SetData(DataFormats.Text,true,textBox1.Text);
m_data.SetData(DataFormats.Bitmap,true,pictureBox1.Image);
Clipboard.SetDataObject(m_data,true);
Now you can paste both into Notepad as well as into any Graphics application that allows you to paste a Bitmap into it.
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Last Updated: 27 Apr 2002 Editor: Chris Maunder |
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