Using GCD in performSelectorInBackground: , How this action get an exception? - ios

Question

When I call "performSelectorInBackground" to process some action asynchronously.
My code struct is like:
[self performSelectorInBackground:#selector(AddTheAdditionalDataSourceToTableView) withObject:nil];
and AddTheAdditionalDataSourceToTableView's code struct is like :
-(void)AddTheAdditionalDataSourceToTableView
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
...
dispatch_async(dispatch_get_current_queue(), ^{
...
});
...
});
}
and after the viewController call 'popViewController', dealloc will never be called!!!
I know I can just call 'AddTheAdditionalDataSourceToTableView' directly. it will process asynchronously and it works fine. dealloc will called when the viewController did disappear.But I don't know why calling it using "performSelectorInBackground" will cause this exception above.
: (
- (void)reloadTableViewDataSource
{
// should be calling your tableviews data source model to reload
// put here just for demo
[self performSelectorInBackground:#selector(reFreshTableView) withObject:nil];
//[self reFreshTableView];
}
- (void)reFreshTableView
{
NSString *myPoint = [self currentLocationPoint];
if (!myPoint || [myPoint isEqualToString:#""]) {
[self enableButtons];
[tableView tableViewDidFinishedLoading];
return;
}
Interface *interface = [[Interface alloc]init];
/* 默认从page 1开始刷新数据 */
[self disableButtons];
_interface = (id)interface;
interface.delegate = self;
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
[interface aroundInfoFromServiceInterface:_distanceType
withTableType:_tableType
withSortType:_sortType
withPageNum:1
withNumPerPage:NumberOfCellInOneRequest withPoint:myPoint];
});
//[interface release];
//[tableView flashMessage:#"hahahah"];
}
- (void)aroundInfoFromServiceInterface:(NSInteger)distance
withTableType:(NSInteger)tableType
withSortType:(NSInteger)sortType
withPageNum:(NSInteger)pageNum
withNumPerPage:(NSInteger)numPerPage
withPoint:(NSString *)myPiont
{
RequestData *data1 = [RequestData requestData:[NSString stringWithFormat:#"%d", distance] key:#"aroundDistant"];
RequestData *data2 = [RequestData requestData:[NSString stringWithFormat:#"%d", tableType] key:#"itemType"];
RequestData *data3 = [RequestData requestData:[NSString stringWithFormat:#"%d", sortType] key:#"sortType"];
RequestData *data4 = [RequestData requestData:[NSString stringWithFormat:#"%d", pageNum] key:#"pageNum"];
RequestData *data5 = [RequestData requestData:[NSString stringWithFormat:#"%d", numPerPage] key:#"numPerPage"];
RequestData *data6 = [RequestData requestData:[NSString stringWithFormat:#"%#", myPiont] key:#"mappoint"];
NSLog(#"%# , %# , %# , %# , %# , %#" , [NSString stringWithFormat:#"%d", distance] ,[NSString stringWithFormat:#"%d", tableType] ,[NSString stringWithFormat:#"%d", sortType] , [NSString stringWithFormat:#"%d", pageNum], [NSString stringWithFormat:#"%d", numPerPage] , [NSString stringWithFormat:#"%#", myPiont]);
NSArray *tempArray = [NSArray arrayWithObjects:data1, data2, data3, data4, data5, data6, nil];
DataFromService *dataFromService = [[[DataFromService alloc]init]autorelease];
dispatch_async(dispatch_get_main_queue(), ^{
NSString *strContent = [dataFromService requestData:tempArray fromURL:tableType == 0?AROUND_FRIEND_INFO_URL:AROUND_FISHING_STORE_AND_AREA_INFO_URL];
NSArray *responseArray = (NSArray *)[self checkRequestResponse:strContent];
if (responseArray) {
NSMutableArray *tempArray = [[NSMutableArray alloc]init];
switch (tableType) {
case TableType_FrinedsAround:
tempArray = [[FormatData shareInstance] formatDictToFriendsAround:responseArray];
break;
case TableType_FishingStoreAround:
tempArray = [[FormatData shareInstance] formatDictToFishingStoreAround:responseArray];
break;
case TableType_FishingAreaAround:
tempArray = [[FormatData shareInstance] formatDictToFishingAreaAround:responseArray];
break;
default:
break;
}
if (self.delegate && [self.delegate respondsToSelector:#selector(requestDataSuccess:responses:)]) {
[self.delegate requestDataSuccess:self responses:tempArray];
return;
}
}
});
}

Answer 1

dispatch_get_current_queue()
Gets a background queue, because you are using performSelectorInBackground, it gets called from a background queue.
dispatch_get_main_queue()
dispatch_async returns immediately, so you don't need to use performSelectorInBackground:. You can just call dispatch_async directly:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
...
dispatch_async(dispatch_get_main_queue(), ^{
...
});
...
});