为什么在那里保存和加载文件代码可在iPhone模拟器上运行但在设备上失败

Question

(void) loadDataFromDisk
{
    NSMutableData *data = [[NSMutableData alloc] initWithContentsOfFile:[self pathToDataFile]];
    NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];


    _cells = [[unarchiver decodeObjectForKey:@"Board"] retain];

    [unarchiver release];
    [data release]; 
}

(void) saveDataToDisk
{   
    NSMutableData *data = [NSMutableData alloc];
    NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
    [archiver encodeObject:_cells forKey:@"Board"];

    [archiver finishEncoding];

    [data writeToFile:[self pathToDataFile] atomically:YES];

    //[array release];  
    [data release];
    //NSMutableData 
}

(BOOL)gameDataExists
{
    return [[NSFileManager defaultManager] fileExistsAtPath:[self pathToDataFile]];
}

(NSString *)pathToDataFile
{
    NSString *path = [[NSBundle mainBundle] bundlePath];
    return [path stringByAppendingPathComponent: GAME_DAT];
}

the code above worked on simulator but failed on device.it seems like that the file can not be found after i exit and reload my app. And if i implement the pathToDataFile like this:

(NSString *)pathToDataFile
{
    NSArray * path = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory , NSUserDomainMask, YES);
    NSString *docDir = [path objectAtIndex:0];
    return [docDir stringByAppendingPathComponent:GAME_DAT];
}

the file save and reload worked on device ,but the drawRect method i implemented in my view can not be called after i called [self setNeedsDisplay].

chris Can

Answer 1

The bundle path is read-only on the device but read-write on the emulator. On the device any attempts to write there will therefore fail.

Your second approach to use document directory should solve the problem.

I don't know why [self setNeedsDisplay] doesn't work for you but it's likely unrelated to this problem.

There is one error I noticed in your code:

NSMutableData *data = [NSMutableData alloc];

Should be:

NSMutableData *data = [[NSMutableData alloc] init];

You should also release the archiver at the end of the saveDataToDisk method.