摘自：蘋果文檔
non-concurrrent
#import "LoadOperation.h"
// key for obtaining the current scan count
NSString *kScanCountKey = @"scanCount";
// key for obtaining the path of an image fiel
NSString *kPathKey = @"path";
// key for obtaining the size of an image file
NSString *kSizeKey = @"size";
// key for obtaining the name of an image file
NSString *kNameKey = @"name";
// key for obtaining the mod date of an image file
NSString *kModifiedKey = @"modified";
// NSNotification name to tell the Window controller an image file as found
NSString *kLoadImageDidFinish = @"LoadImageDidFinish";
@interface LoadOperation ()
{
NSURL *loadURL;
NSInteger ourScanCount;
}
@property (retain) NSURL *loadURL;
@end
@implementation LoadOperation
@synthesize loadURL;
// -------------------------------------------------------------------------------
// initWithPath:path
// -------------------------------------------------------------------------------
- (id)initWithURL:(NSURL *)url scanCount:(NSInteger)scanCount
{
self = [super init];
if (self)
{
self.loadURL = url;
ourScanCount = scanCount;
}
return self;
}
// -------------------------------------------------------------------------------
// isImageFile:filePath
//
// Uses LaunchServices and UTIs to detect if a given file path is an image file.
// -------------------------------------------------------------------------------
- (BOOL)isImageFile:(NSURL *)url
{
BOOL isImageFile = NO;
NSString *utiValue;
[url getResourceValue:&utiValue forKey:NSURLTypeIdentifierKey error:nil];
if (utiValue)
{
isImageFile = UTTypeConformsTo((__bridge CFStringRef)utiValue, kUTTypeImage);
}
return isImageFile;
}
// -------------------------------------------------------------------------------
// main:
//
// Examine the given file (from the NSURL "loadURL") to see it its an image file.
// If an image file examine further and report its file attributes.
//
// We could use NSFileManager, but to be on the safe side we will use the
// File Manager APIs to get the file attributes.
// -------------------------------------------------------------------------------
- (void)main
{
if (![self isCancelled])
{
// test to see if it's an image file
if ([self isImageFile:loadURL])
{
// in this example, we just get the file's info (mod date, file size) and report it to the table view
//
NSNumber *fileSize;
[self.loadURL getResourceValue:&fileSize forKey:NSURLFileSizeKey error:nil];
NSDate *fileCreationDate;
[self.loadURL getResourceValue:&fileCreationDate forKey:NSURLCreationDateKey error:nil];
NSDateFormatter* formatter = [[NSDateFormatter alloc] init];
[formatter setTimeStyle:NSDateFormatterNoStyle];
[formatter setDateStyle:NSDateFormatterShortStyle];
NSString *modDateStr = [formatter stringFromDate:fileCreationDate];
NSDictionary *info = [NSDictionary dictionaryWithObjectsAndKeys:
[self.loadURL lastPathComponent], kNameKey,
[self.loadURL absoluteString], kPathKey,
modDateStr, kModifiedKey,
[NSString stringWithFormat:@"%ld", [fileSize integerValue]], kSizeKey,
[NSNumber numberWithInteger:ourScanCount], kScanCountKey, // pass back to check if user cancelled/started a new scan
nil];
if (![self isCancelled])
{
// for the purposes of this sample, we're just going to post the information
// out there and let whoever might be interested receive it (in our case its MyWindowController).
//
[[NSNotificationCenter defaultCenter] postNotificationName:kLoadImageDidFinish object:nil userInfo:info];
}
}
}
}
@end
concurrrent
@interface MyOperation : NSOperation {
BOOL executing;
BOOL finished;
}
- (void)completeOperation;
@end
@implementation MyOperation
- (id)init {
self = [super init];
if (self) {
executing = NO;
finished = NO;
}
return self;
}
- (BOOL)isConcurrent {
return YES;
}
- (BOOL)isExecuting {
return executing;
}
- (BOOL)isFinished {
return finished;
}
@end
*****************
- (void)start {
// Always check for cancellation before launching the task.
if ([self isCancelled])
{
// Must move the operation to the finished state if it is canceled.
[self willChangeValueForKey:@"isFinished"];
finished = YES;
[self didChangeValueForKey:@"isFinished"];
return;
}
// If the operation is not canceled, begin executing the task.
[self willChangeValueForKey:@"isExecuting"];
[NSThread detachNewThreadSelector:@selector(main) toTarget:self withObject:nil];
executing = YES;
[self didChangeValueForKey:@"isExecuting"];
}
**************
- (void)main {
@try {
// Do the main work of the operation here.
[self completeOperation];
}
@catch(...) {
// Do not rethrow exceptions.
}
}
- (void)completeOperation {
[self willChangeValueForKey:@"isFinished"];
[self willChangeValueForKey:@"isExecuting"];
executing = NO;
finished = YES;
[self didChangeValueForKey:@"isExecuting"];
[self didChangeValueForKey:@"isFinished"];
}
