用于读写临时数据的方法

bool writeApplicationData(NSData *data, NSString *fileName)
{
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
if (!documentsDirectory) {
NSLog(@"Documents directory not found!");
return NO;
}
NSString *appFile = [documentsDirectory stringByAppendingPathComponent:fileName];
return ([data writeToFile:appFile atomically:YES]);
}

NSData *applicationDataFromFile(NSString *fileName)
{
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *appFile = [documentsDirectory stringByAppendingPathComponent:fileName];
NSData *myData = [[[NSData alloc] initWithContentsOfFile:appFile] autorelease];
return myData;
}