最近項目需求，一個界面有多個請求，希望請求完才做操作，這時候我很快會想到用請求隊列。
1.創(chuàng)建線程組
dispatch_group_t group = dispatch_group_create();
2.然后一下子請求了五個請求，如下：
dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//請求1
? ? ? ?[self Request1];
});
dispatch_group_async(group,?dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,?0),?^{
? ? ? [self Request2];
});
dispatch_group_async(group,?dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,?0),?^{
? ? ? [self Request3];
});
dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
[self Request4];
});
dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
[self Request5];
});
dispatch_group_notify(group,?dispatch_get_main_queue(),?^{
//界面刷新
? ? [_orderDetailTableView reloadData];
});
自信滿滿的以為完事了，結(jié)果運行一看發(fā)現(xiàn)界面上的數(shù)據(jù)沒有刷新出來
上下滑動多次數(shù)據(jù)才出來，這時候我在想哪里出問題，原來造成的問題為多個請求均加載完成，但界面已在未得到數(shù)據(jù)前提前刷新導(dǎo)致界面空白。
這時候我想起了用GCD中信號量dispatch_semaphore進行實現(xiàn)
dispatch_semaphore信號量為基于計數(shù)器的一種多線程同步機制。用于解決在多個線程訪問共有資源時候，會因為多線程的特性而引發(fā)數(shù)據(jù)出錯的問題。
如果semaphore計數(shù)大于等于1，計數(shù)-1，返回，程序繼續(xù)運行。如果計數(shù)為0，則等待。
dispatch_semaphore_signal(semaphore)為計數(shù)+1操作。dispatch_semaphore_wait(sema,DISPATCH_TIME_FOREVER)為設(shè)置等待時間
//獲取箱子詳情
- (void)Request1
{
//創(chuàng)建信號量并設(shè)置計數(shù)默認(rèn)為0
dispatch_semaphore_t sema = dispatch_semaphore_create(0);
[[NetTool sharedNetTool]GetShipmentDetailWithBindMark:self.blinder ExpressCode:self.experid Success:^(id obj) {
[[TipViewTool sharedTipViewTool]stopanimal:self];
if (reqSuccess)
{
//計數(shù)+1操作
dispatch_semaphore_signal(sema);
for(NSDictionary * dic in? obj[@"Data"])
{
ShopingDetailMod * mod = [ShopingDetailMod new];
[mod setValuesForKeysWithDictionary:dic];
[self.boxDetailArr addObject:mod];
}
if(self.boxDetailArr.count>0)
{
ShopingDetailMod * mod =self.boxDetailArr[0];
if (mod.NotMergeChargeDetails.count==0)
{
self.ExpressBoxState = @"2";
}
}
}
} Failure:^(NSError *error) {
}];
//若計數(shù)為0則一直等待
dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
}
ok.,完美解決問題，數(shù)據(jù)出來了
