C# 4 and .NET 4

editing a Text Document: The Capseditor example ❘ OC37
longest. For both height and width, you will also want to make an allowance for a small margin around the
displayed document to make the application look more attractive.
The following is the method that calculates the document size:
private void CalculateDocumentSize()
{
if (!documentHasData)
{
documentSize = new Size(100, 200);
}
else
{
documentSize.Height = (int)(nLines*lineHeight) + 2*(int)margin;
uint maxLineLength = 0;
foreach (TextLineInformation nextWord in documentLines)
{
uint tempLineLength = nextWord.Width;
if (tempLineLength > maxLineLength)
{
maxLineLength = tempLineLength;
}
}
maxLineLength += 2*margin;
documentSize.Width = (int)maxLineLength;
}
AutoScrollMinSize = documentSize;
}
code download CapsEditor.sln
This method first checks whether there is any data to be displayed. If there is not, then you cheat a bit and
use a hard-coded document size, which is big enough to display the big red warning.
If you had wanted to really do it properly, you would have used MeasureString() to check how big that
warning actually is.
When you have worked out the document size, you tell the Form instance what the size is by setting the
Form.AutoScrollMinSize property. When you do this, something interesting happens behind the scenes.
In the process of setting this property, the client area is invalidated and a Paint event is raised, for the
very sensible reason that changing the size of the document means scrollbars will need to be added or
modified and the entire client area will almost certainly be repainted. Why is that interesting If you look
back at the code for LoadFile(), you will realize that the call to Invalidate() in that method is actually
redundant. The client area will be invalidated anyway when you set the document size. The explicit call to
Invalidate() was left in the LoadFile() implementation to illustrate how you should normally do things.
In fact, in this case, calling Invalidate() again will only needlessly request a duplicate Paint event.
However, this in turn illustrates how Invalidate() gives Windows the chance to optimize performance.
The second Paint event will not, in fact, get raised: Windows will see that there is a Paint event already
sitting in the queue and will compare the requested invalidated regions to see if it needs to do anything to
merge them. In this case, both Paint events will specify the entire client area, so nothing needs to be done,
and Windows will quietly drop the second Paint request. Of course, going through that process will take
up a little bit of processor time, but it will be a negligible amount of time compared to how long it takes to
actually do some painting.
onPaint()
Now that you have seen how CapsEditor loads the file, it’s time to look at how the painting is done:
protected override void OnPaint(PaintEventArgs e)
{
base.OnPaint(e);
Graphics dc = e.Graphics;
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