- (NSString *)getAuthorizationHeader{
iKMAppDelegate *delegate = (iKMAppDelegate *)[UIApplication sharedApplication].delegate;
NSString *header = [NSString stringWithFormat:@"Bearer %@",delegate.appDataObject.oauth2AcessToken];
return header;
}
这个方法会在XCode9中收到警告
[UIApplication delegate] must be called from main thread only
解决方法
在主线程上无法访问UIApplication的委托,但您可以使用dispatch_sync轻松完成
- (NSString *)getAuthorizationHeader{
__block iKMAppDelegate *delegate;
if([NSThread isMainThread]) {
delegate = (iKMAppDelegate *)[UIApplication sharedApplication].delegate;
} else {
dispatch_sync(dispatch_get_main_queue(),^{
delegate = (iKMAppDelegate *)[UIApplication sharedApplication].delegate;
});
}
NSString *header = [NSString stringWithFormat:@"Bearer %@",delegate.appDataObject.oauth2AcessToken];
return header;
}
与dispatch_async相反,dispatch_sync函数将一直等到它传递的块完成后再返回.
使用dispatch_sync,有必要检查是否未从主线程执行该函数,这会导致死锁.