从字典中获取值

问题描述

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stRs232Timer* pEvent;
pEvent = (stRs232Timer*)[m_cAppIdMap objectForKey:[NSNumber numberWithUnsignedShort:wTimerIds]];

我收到EXC_BAD_ACCESS错误。为什么会这样？ 编辑：

-(BOOL)createTimer
{
    stRs232Timer*   pEvent = malloc(sizeof(stRs232Timer));

    pEvent->bPersistent = YES;                              // setup timer structure
    //pEvent->pStack      = pStack;
    pEvent->wAppTimerId = 95;
    pEvent->uPeriod     = 50;
    pEvent->bStopped    = NO;
    pEvent->uExpirationTime = 10;

    NSLog(@\"bPersistent:%d\",pEvent->bPersistent);
    NSLog(@\"wAppTimerId:%d\",pEvent->wAppTimerId);
    NSLog(@\"uPeriod:%d\",pEvent->uPeriod);
    NSLog(@\"bStopped:%d\",pEvent->bStopped);


    NSData* myData = [NSData dataWithBytes:(void*)pEvent length:sizeof(stRs232Timer*)];

    wTimerId = 99;
    pEvent->uPeriod = 51;
    myData = [NSData dataWithBytes:(void*)pEvent length:sizeof(stRs232Timer*)];
    [m_cAppIdMap setobject:myData forKey:[NSNumber numberWithUnsignedShort:wTimerId]];
    wTimerId = 96;
    pEvent->uPeriod = 52;
    myData = [NSData dataWithBytes:(void*)pEvent length:sizeof(stRs232Timer*)];
    [m_cAppIdMap setobject:myData forKey:[NSNumber numberWithUnsignedShort:wTimerId]];
    wTimerId = 97;
    pEvent->uPeriod = 53;
    myData = [NSData dataWithBytes:(void*)pEvent length:sizeof(stRs232Timer*)];
    [m_cAppIdMap setobject:myData forKey:[NSNumber numberWithUnsignedShort:wTimerId]];
    wTimerId = 98;
    pEvent->uPeriod = 54;
    myData = [NSData dataWithBytes:(void*)pEvent length:sizeof(stRs232Timer*)];
    [m_cAppIdMap setobject:myData forKey:[NSNumber numberWithUnsignedShort:wTimerId]];
    wTimerId = 95;
    pEvent->uPeriod = 55;
    myData = [NSData dataWithBytes:(void*)pEvent length:sizeof(stRs232Timer*)];
    [m_cAppIdMap setobject:myData forKey:[NSNumber numberWithUnsignedShort:wTimerId]];

    NSLog(@\"The dictionary count Now is:%d\",[m_cAppIdMap count]);
    NSLog(@\"The dictionary values Now is:\");
    NSLog(@\"%@\",m_cAppIdMap);


    [m_cPendingEventList addobject:myData];
    NSLog(@\"EventList:%@\",m_cPendingEventList);

    [self StopTimer:99];

return YES;
}

-(BOOL)StopTimer:(unsigned short)wTimerIds
{
    NSLog(@\"Into the StopTimer!!\");
    stRs232Timer* pEvent;
    BOOL bReturn = NO;
    pEvent = (stRs232Timer*)[m_cAppIdMap objectForKey:[NSNumber numberWithUnsignedShort:wTimerIds]];

    if ([theLock tryLock]) {
        int cnts = [m_cAppIdMap count];
        NSLog(@\"The count is:%d\",cnts);
           if(pEvent!=nil)
            {
                pEvent->bStopped = YES;
                [m_cAppIdMap removeObjectForKey:[NSNumber numberWithUnsignedShort:wTimerIds]];
                bReturn = YES;
            }
    }
    NSLog(@\"My Dictionary value Now is:%@\",m_cAppIdMap);
    [theLock unlock];
    return bReturn;
}

我调试了代码，以查看导致此异常的位置。[m_cAppIdMap removeObjectForKey：[NSNumber numberWithUnsignedShort：wTimerIds]]; 在stopTimer里面。 stRs232Timer是指向使用NSData作为NSObject存储在NSDictionary上的结构的指针。     

解决方法

您确定代码崩溃了吗？如果

wTimerIds

是一个无符号的short，则如果键不存在，则字典将返回

nil

。即使未定义字典，向“ 3”对象发送消息也是有效的，因此不会导致崩溃。 因此，我认为： 1.飞机坠毁在其他地方 2.

wTimerIds

不是无符号的短路     ,

m_cAppIdMap

可能已过早释放。您可以运行探查器（使用“僵尸”工具），如果是这种情况，您将在尝试调用objectForKey时收到一条错误消息，指出一条消息已发送到已释放的对象，您将收到一条错误消息。