在Objective-C中创建制表符分隔文件

Question

I found this snippet online to write, and then append data to a text file:

- (void)appendText:(NSString *)text toFile:(NSString *)filePath {

    // NSFileHandle won't create the file for us, so we need to check to make sure it exists
    NSFileManager *fileManager = [NSFileManager defaultManager];
    if (![fileManager fileExistsAtPath:filePath]) {

        // the file doesn't exist yet, so we can just write out the text using the 
        // NSString convenience method

        NSError *error = noErr;
        BOOL success = [text writeToFile:filePath atomically:YES encoding:NSUTF8StringEncoding error:&error];
        if (!success) {
            // handle the error
            NSLog(@"%@", error);
        }

    } 
    else {

        // the file already exists, so we should append the text to the end

        // get a handle to the file
        NSFileHandle *fileHandle = [NSFileHandle fileHandleForWritingAtPath:filePath];

        // move to the end of the file
        [fileHandle seekToEndOfFile];

        // convert the string to an NSData object
        NSData *textData = [text dataUsingEncoding:NSUTF8StringEncoding];

        // write the data to the end of the file
        [fileHandle writeData:textData];

        // clean up
        [fileHandle closeFile];
    }
}

This makes sense to me. I have a class that has 3 properties, of NSString, NSInteger, and NSString. When I try to use this method, I do this:

for (MyObject *ref in array) {
    NSString *stringToFile = [NSString stringWithFormat:@"%@\t%i\t%@", ref.ChrID, ref.Position, ref.Sequence];
    [self appendText:stringToFile toFile:filePath];
}

It doesn't look quite right. My data looks like this:

NSString *tab* NSInteger *single space* NSStringNSString *tab* NSInteger newline
NSStringNSString *tab* NSInteger newline 
NSStringNSString *tab* NSInteger newline
NSStringNSString *tab* NSInteger newline
NSStringNSString *tab* NSInteger newline
NSStringNSString *tab* NSInteger newline
NSStringNSString *tab* NSInteger newline
NSStringNSString *tab* NSInteger newline
...

I'm not sure what is going on to make it look like this. When I NSLog the data, it looks fine. But something with the first line gets messed up, and then everything seems to be off. Any thoughts? Thanks.

Answer 1

There are several issues with the method appendText :

• if the file does not exist, the first line is written with the NSString writeToFile method without the \\n

• following lines are written with the NSData writeData method

• it's very inefficient to use a filemanager to check for existence, get a filehandle, seek to EOF and then write just one line, omitting the close too. And repeating this for every following line.

So better do it this way:

• get the filehandle for writing, it will be created if it's not there yet

• seek to EOF

• do your loop with writeData for each line

• close the file