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@dhoerl dhoerl/HowTo.txt
Created Jan 27, 2012

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Converting a NSDictionary to a Binary PList
When I posted this on Apple’s Cocoadev listserver, I never did get pointers to code to convert a NSDictionary to a binary formatted plist, but did get pointers to look at NSPropertyListSerialization - something I had already (mis)read a few times.
The description for the dataFromPropertyList class method seems confusing if you don't understand that you can create a property list with no keys: that is, you can create one with a single compliant object, and the key becomes "root".
So, in the unlikely event that some else someday has the same mental block, here is actual tested code that takes a NSDictionary and creates a binary plist file:
NSDictionary *dict;
char *payload = "This is the payload";
dict = [NSDictionary dictionaryWithObjectsAndKeys:
@"Hello world", @"greeting",
[NSData dataWithBytes:payload length:strlen(payload)], @"payload",
[NSNumber numberWithInt:10], @"result",
nil ];
// get a text representation, for comparison
[dict writeToFile:@"/tmp/text.plist" atomically:NO];
NSString *err = nil;
NSData *plist;
NSFileManager *manager;
BOOL ret;
manager = [NSFileManager defaultManager];
plist = [NSPropertyListSerialization dataFromPropertyList:dict
format:NSPropertyListBinaryFormat_v1_0
errorDescription:&err];
if(plist == nil) {
NSLog(@"NSPropertyListSerialization error: %@", err);
return -1;
}
ret = [manager createFileAtPath:@"/tmp/binary.plist" contents:plist attributes:nil];
if(ret == NO) {
NSLog(@"Create failed");
return -1;
}
Just to prove to myself that yes, you can create a property list with other objects like NSNumbers or raw NSData, I added these two tests:
plist = [NSPropertyListSerialization dataFromPropertyList:[NSNumber numberWithInt:1]
format:NSPropertyListBinaryFormat_v1_0
errorDescription:&err];
if(plist == nil) {
NSLog(@"NSPropertyListSerialization error: %@", err);
return -1;
}
ret = [manager createFileAtPath:@"/tmp/tst1.plist" contents:plist attributes:nil];
if(ret == NO) {
NSLog(@"Create failed");
return -1;
}
plist = [NSPropertyListSerialization dataFromPropertyList:[NSData dataWithBytes:payload length:strlen(payload)]
format:NSPropertyListBinaryFormat_v1_0
errorDescription:&err];
if(plist == nil) {
NSLog(@"NSPropertyListSerialization error: %@", err);
return -1;
}
ret = [manager createFileAtPath:@"/tmp/tst2.plist" contents:plist attributes:nil];
if(ret == NO) {
NSLog(@"Create failed");
return -1;
}
Then, Ken Thomases (on Cocoadev) provided a shorter version, by having the NSData instance write the file. Jean-Daniel Dupas suggested using CFPropertyListWriteToStream to bypass the intermediate NSData object (a speed and memory footprint improvement). Here is the above code wrapped in a short command line test program:
int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
NSString *err = nil;
NSData *plist;
NSDictionary *dict;
char *payload = "This is the payload";
dict = [NSDictionary dictionaryWithObjectsAndKeys:
@"Hello world", @"greeting",
[NSData dataWithBytes:payload length:strlen(payload)], @"payload",
[NSNumber numberWithInt:10], @"result",
nil ];
// 1 - get a XML (text) file representation
[dict writeToFile:@"/tmp/text.plist" atomically:NO];
// get a binary file representation - creates an additional NSData in memory object
plist = [NSPropertyListSerialization dataFromPropertyList:dict
format:NSPropertyListBinaryFormat_v1_0
errorDescription:&err];
if(plist == nil) {
NSLog(@"NSPropertyListSerialization error: %@", err);
return -1;
}
// 2 - have the NSData object save a binary representation
[plist writeToFile:@"/tmp/binary1.plist" atomically:NO];
// get a binary file representation - no additional memory footprint
// NOTE: documentation does not state it, but NSOutputStream creates the file if it does not yet exist
NSOutputStream *str = [NSOutputStream outputStreamToFileAtPath:@"/tmp/binary2.plist" append:NO];
if(str == nil) {
NSLog(@"cannot create output stream");
return -1;
}
// 3 - stream a binary representation
[str open];
CFIndex idx = CFPropertyListWriteToStream(dict, (CFWriteStreamRef)str, kCFPropertyListBinaryFormat_v1_0, (CFStringRef *)&err);
if(idx == 0) {
NSLog(@"CFPropertyListWriteToStream error: %x %@", err, err);
return -1;
}
[str close];
[pool drain];
return 0;
}
Hope this is of use to someone else.
@dhoerl

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commented Jan 27, 2012

Originally posted in 2008 on my iWeb site (iWeb is going away soon).

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