iOS:dispatch_get_global_queue QOS_CLASS_BACKGROUND在7.1.2崩溃

Question

我有以下代码片段,通过使用块获取联系人:

if (&ABAddressBookCreateWithOptions != NULL) {
            CFErrorRef error = nil;

            addressBook = ABAddressBookCreateWithOptions(NULL, &error);

            ABAddressBookRequestAccessWithCompletion(addressBook, ^(bool granted, CFErrorRef error) {

                dispatch_sync(dispatch_get_main_queue(), ^{
                        if (error) {
                            //...
                        } else if (!granted) {
                            //...
                        } else {
                            // access granted
                          //...
                        }
                    });
                });

它适用于两者7.1.2和8.1.3版本.

然而,当我试图改变dispatch_get_main_queue到dispatch_get_global_queue(QOS_CLASS_BACKGROUND, 0)它的工作原理上8.1.3却崩溃上7.1.2

if (&ABAddressBookCreateWithOptions != NULL) {
                CFErrorRef error = nil;

                addressBook = ABAddressBookCreateWithOptions(NULL, &error);

                ABAddressBookRequestAccessWithCompletion(addressBook, ^(bool granted, CFErrorRef error) {
                        dispatch_sync(dispatch_get_global_queue(QOS_CLASS_BACKGROUND, 0), ^{ // BAD ACCESS
                    if (error) {
                                //...
                            } else if (!granted) {
                                //...
                            } else {
                                // access granted
                              //...
                            }
                        });
                    });

Answer 1

该QOS_CLASS_标识符的iOS 8引入您需要使用DISPATCH_QUEUE_PRIORITY_,如果你想支持的iOS 7的标识符.