How to save a text document in Cocoa with specified NSString encoding?

Question

I'm trying to create a simple text editor like Textedit for Mac OS X, but after many hours of research can't figure out how to correctly write my document's data to a file. I'm using the Cocoa framework and my application is document-based. Looking around in the Cocoa API I found a brief tutorial, "Building a text editor in 15 minutes" or something like this, that implements the following method to write the data to a file:

- (NSData *)dataOfType:(NSString *)typeName error:(NSError **)outError {
    [textView breakUndoCoalescing];
    NSAttributedString *string=[[textView textStorage] copy];
    NSData *data;
    NSMutableDictionary *dict=[NSDictionary dictionaryWithObject:NSPlainTextDocumentType forKey:NSDocumentTypeDocumentAttribute];
    data=[string dataFromRange:NSMakeRange(0,[string length]) documentAttributes:dict error:outError];
    return data;
}

This just works fine, but I'd like to let the user choose the text encoding. I guess this method uses an "automatic" encoding, but how can I write the data using a predefined encoding? I tried using the following code:

- (NSData *)dataOfType:(NSString *)typeName error:(NSError **)outError {
    [textView breakUndoCoalescing];
    NSAttributedString *string=[[textView textStorage] copy];
    NSData *data;
    NSInteger saveEncoding=[prefs integerForKey:@"saveEncoding"];
    // if the saving encoding is set to "automatic"
    if (saveEncoding<0) {
        NSMutableDictionary *dict=[NSDictionary dictionaryWithObject:NSPlainTextDocumentType forKey:NSDocumentTypeDocumentAttribute];
        data=[string dataFromRange:NSMakeRange(0,[string length]) documentAttributes:dict error:outError];
    // else use the encoding specified by the user
    } else {
        NSMutableDictionary *dict=[NSDictionary dictionaryWithObjectsAndKeys:NSPlainTextDocumentType,NSDocumentTypeDocumentAttribute,saveEncoding,NSCharacterEncodingDocumentAttribute,nil];
        data=[string dataFromRange:NSMakeRange(0,[string length]) documentAttributes:dict error:outError];
    }
    return data;
}

saveEncoding is -1 if the user didn't set a specific encoding, otherwise one of the encodings listed in [NSString availableStringEncodings]. But whenever I try to save my document in a different encoding from UTF8, the app crashes. The same happens when I try to encode my document with the following code:

NSString *string=[[textView textStorage] string];
data=[string dataUsingEncoding:saveEncoding];

What am I doing wrong? It would be great if someone knows how Textedit solved this problem.

kennytm kennytm · Accepted Answer · 2011-03-12T10:53:15

Perhaps you remember that NSDictionary can only store objects...

NSMutableDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:
  NSPlainTextDocumentType,
    NSDocumentTypeDocumentAttribute,
  [NSNumber numberWithInteger:saveEncoding],
    NSCharacterEncodingDocumentAttribute,
  nil];

How to save a text document in Cocoa with specified NSString encoding?

1 Answers