NSOperationQueue 以及 NSOperation 在 iOS 5 下的问题

来源：互联网发布：泸州网络问政平台app 编辑：程序博客网时间：2024/05/21 17:35

近期将xcode升级到了4.2，SDK是 iOS5。在 iOS 5 下，以前可以正常工作的 NSOperation，会崩溃。崩溃的原因是：取消队列中的操作，但是该操作还没有开始。

解决这个问题的方法是：

在 start 方法中判断操作是否已经取消，如果取消，结束操作，没有取消，再执行操作。

在 cancel 方法中判断操作是否正在执行，如果在执行，结束操作，如果没有，修改操作的isCancelled状态。

头文件：

#import <Foundation/Foundation.h>@interface FMURLRequest : NSOperation {        BOOL _isReady;    BOOL _isCancelled;    BOOL _isExecuting;    BOOL _isFinished;}- (void)cancel;@end

实现文件：

#import "FMURLRequest.h"@interface FMURLRequest ()- (BOOL)isReady;- (BOOL)isExecuting;- (BOOL)isFinished;- (BOOL)isCancelled;- (BOOL)isConcurrent;- (void)start;- (void)finish;@end@implementation FMURLRequest- (id)init {        if ((self = [super init])) {        _isCancelled = NO;        _isExecuting = NO;        _isFinished = NO;        _isReady = YES;    }        return self;}- (void)dealloc {        [super dealloc];}#pragma -#pragma mark Operation Management & Super Class Methods- (BOOL)isReady {        return _isReady;}- (BOOL)isExecuting {        return _isExecuting;}- (BOOL)isFinished {        return _isFinished;}- (BOOL)isCancelled {        return _isCancelled;}- (BOOL)isConcurrent {        return YES;}- (void)start {if (![NSThread isMainThread]) {        [self performSelectorOnMainThread:@selector(start) withObject:nil waitUntilDone:NO];        return;    }        [self willChangeValueForKey:@"isExecuting"];    _isExecuting = YES;    [self didChangeValueForKey:@"isExecuting"];if ([self isCancelled]) {[self finish];return;}        // TODO: start operation}- (void)finish {        [self willChangeValueForKey:@"isExecuting"];    [self willChangeValueForKey:@"isFinished"];        _isExecuting = NO;    _isFinished = YES;        [self didChangeValueForKey:@"isExecuting"];    [self didChangeValueForKey:@"isFinished"];}- (void)cancel {        [self willChangeValueForKey:@"isCancelled"];    _isCancelled = YES;    [self didChangeValueForKey:@"isCancelled"];        if ([self isExecuting] == YES) {        // TODO: clean resource        [self finish];    }}@end