[Drawkit] any help with read/write

[Brad Larson]

On Aug 7, 2008, at 9:50 PM, James Maxwell wrote:

> In particular, I'm wondering how to get a DKDrawingDocument-based  
> app to save to my own file type, extension, and all that. I have it  
> working, for now, just using the defaults of "Drawing" and  
> ".drawing", but I'd like to get my own file type and extension  
> implemented.
>
> A quick list of steps would be a huge help.
>

First, you'll want to create a category on DKDrawing that will handle  
your custom file format.  Within that category, create two methods, a  
class method that takes in an NSData object and returns a new  
DKDrawing, and an instance method that returns an NSData object.  The  
first is your loading method, the second your saving one.

Next, you'll need to set up the file extension or UTI to use in your  
application's Info.plist.  To set up a simple file extension, go to  
your Xcode project, click on the Targets tab, click on your  
application's target, and click the Get Info button.  In the  
inspector, go to the Properties tab and add a new document type.  Give  
it a name (for example "Pattern"), leave the UTI field blank, set the  
appropriate extension (or extensions) for this file format, set the  
class to be your new custom document class, give it an icon, and set  
the type to Editor or Viewer as appropriate.

UTIs are a little more involved, and require you to edit the  
Info.plist.  Find the Info.plist in your source files, right-click on  
it, and choose to open it as a plain-text file.  You'll need to add  
XML to export your UTI definition similar to the following:

	<key>UTExportedTypeDeclarations</key>
	<array>
		<dict>
			<key>UTTypeConformsTo</key>
			<array>
				<string>public.xml</string>
			</array>
			<key>UTTypeDescription</key>
			<string>SonoPlot's proprietary XML pattern file type</string>
			<key>UTTypeIdentifier</key>
			<string>com.sonoplot.pattern</string>
			<key>UTTypeTagSpecification</key>
			<dict>
				<key>public.filename-extension</key>
				<array>
					<string>pattern</string>
				</array>
			</dict>
		</dict>
	</array>

This example is for our custom XML-based file format.  Repeat the same  
steps as for setting up a new file extension type, only this time fill  
in the UTI using the one you exported in your Info.plist.   
Unfortunately, UTIs don't always work the way you want, such as when  
another application on your system has claimed the same file extension  
as your application.

Finally, you'll want to call the DKDrawingDocument class methods  
bindFileExportType:toSelector: and bindFileImportType:toSelector: to  
associate your file loading and saving methods from your custom  
category with the new filetype or UTI.  For example, I do

NSString*		kSPPatternDocumentType = @"Pattern";
NSString*		kSPPatternDocumentUTI = @"com.sonoplot.pattern";

[[self class] bindFileExportType:kSPPatternDocumentType  
toSelector:@selector(dataForPattern)];
[[self class] bindFileExportType:kSPPatternDocumentUTI  
toSelector:@selector(dataForPattern)];
[[self class] bindFileImportType:kSPPatternDocumentType  
toSelector:@selector(drawingWithPattern:)];
[[self class] bindFileImportType:kSPPatternDocumentUTI  
toSelector:@selector(drawingWithPattern:)];

in my document's init: method.  I'm going to move that out of there,  
because it only needs to be called once on the start of the program,  
not with each new document.

For a working example of this, I direct you to the code for the beta  
of SonoDraw that we have out there.  I posted this earlier, but I can  
repeat:

The source code is available for download from
http://www.sonoplot.com/sites/default/files/SonoDraw/SonoDrawBeta1.zip
and a compiled binary can be downloaded from
http://www.sonoplot.com/sites/default/files/SonoDraw/SonoDrawBeta1-Binary.zip

Example .pattern files that you can load with the software are also  
available at
http://www.sonoplot.com/sites/default/files/SonoDraw/SamplePatterns.zip

I'm getting close to releasing the final version of this, and I'll be  
sure to post that when it's done.
______________________
Brad Larson
SonoPlot, Inc.
3030 Laura Lane, Suite 120
Middleton, WI 53562