An NSValueTransformer that decompresses NSData into an NSString using my NSData+Bzip2 category (see NSDataPlusBzip). It is reversible. � BryanWoods

// Bzip2ValueTransformer.h @interface Bzip2ValueTransformer : NSValueTransformer

@end

// Bzip2ValueTransformer.m #import “Bzip2ValueTransformer.h” #import “NSData+Bzip2.h”

@implementation Bzip2ValueTransformer

• (Class) transformedValueClass { return [NSString class]; }

• (BOOL) allowsReverseTransformation { return YES; }

• (id) transformedValue:(id)data { // decompress return [[[NSString alloc] initWithData:[data bunzip2] encoding:NSUTF8StringEncoding] autorelease]; }

• (id) reverseTransformedValue:(id)string { // compress return string dataUsingEncoding:NSUTF8StringEncoding] bzip2]; }

@end

---

To give an idea of how it’s used, my test project is just a Cocoa Document-based Application with an [[NSTextView bound (�la CocoaBindings) to an NSData in MyDocument. Selecting Bzip2ValueTransformer in the Bindings palette in Interface Builder handles all of the heavy lifting.

// MyDocument.h @interface MyDocument : NSDocument { NSData * text; }

@end

// MyDocument.m #import “MyDocument.h” #import “Bzip2ValueTransformer.h”

@implementation MyDocument

• (void) initialize { [NSValueTransformer setValueTransformer:Bzip2ValueTransformer new] autorelease] forName:@”Bzip2ValueTransformer”]; }

• (void) dealloc { [text release]; [super dealloc]; }

• ([[NSString *) windowNibName { return @”MyDocument”; }

• (NSData *) dataRepresentationOfType:(NSString *)type { return text; }

• (BOOL) loadDataRepresentation:(NSData *)data ofType:(NSString *)type { text = [data retain]; return (text != nil); }

@end