如何解决从字典中获取值
|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。
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