使用NSFileHandle创建文件后清空文档目录

Question

I'm writing an application for the Apple watch. I'm using the following method (from this SE answer ) to write to a log file:

- (void) writeLogWith: (NSString *) content {

    //Get the file path
    NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
    NSString *fileName = [documentsDirectory stringByAppendingPathComponent:@"whathappened.md"];

    //create file if it doesn't exist
    if(![[NSFileManager defaultManager] fileExistsAtPath:fileName])
        [[NSFileManager defaultManager] createFileAtPath:fileName contents:nil attributes:nil];

    //append text to file (you'll probably want to add a newline every write)
    NSFileHandle *file = [NSFileHandle fileHandleForUpdatingAtPath:fileName];
    [file seekToEndOfFile];
    [file writeData:[content dataUsingEncoding:NSUTF8StringEncoding]];
    [file closeFile];

    return;
}

I'm running it by plugging in my phone and running it directly on my watch. The function is definitely executing (I've stepped thought with the debugger) and it also knows that the file exists and doesn't repeatedly try and create it.

Xcode tells me that the file information is:

Printing description of documentsDirectory:
/var/mobile/Containers/Data/PluginKitPlugin/8503AD6C-6EC9-4522-A867-27109B01B615/Documents
Printing description of documentsDirectory:
(NSString *) documentsDirectory = 0x16d66890
Printing description of fileName:
(NSString *) fileName = 0x16d66950
Printing description of fileName:
/var/mobile/Containers/Data/PluginKitPlugin/8503AD6C-6EC9-4522-A867-27109B01B615/Documents/whathappened.md

I'd like to know if it's writing things correctly, but when I look at the container (following these SE answers ), the documents directory is empty.

My question is: where did my file go? And how can I find it?

Answer 1

I think what might be giving you problems is the NSFileHandle object. I have written thousands upon thousands of files to the documents folder and I have never used NSFileHandle to do this. Simply use the built in method on NSString to write your string to the file path.

Try this:

NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSString *filePath = [[documentsDirectory stringByAppendingPathComponent:@"whathappened"] stringByAppendingPathExtension:@"md"];

if (![[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
    [[NSFileManager defaultManager] createFileAtPath:filePath contents:nil attributes:nil];
}

NSString *string = @"The String You Want To Write.";

NSError *error;
[string writeToFile:filePath atomically:false encoding:NSUTF8StringEncoding error:&error];

if (error) {
    NSLog(@"There was an error writing file\n%@", error.localizedDescription);
}

if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
    NSLog(@"File exists :)");
}
else {
    NSLog(@"File does not exist :(");
}

Answer 2

From other research, the answer appears to be:

If you are storing a file on the Apple Watch, it is stored in it's own container, which isn't visible via xcode.

It indeed, appears to be related to this bug report: https://openradar.appspot.com/radar?id=5021353337946112 , found via this SE: How to export shared container of an iOS App with Xcode6.2?