我的应用有时会在后台崩溃并显示以下崩溃日志:
Nov 7 12:33:31 iPad backboardd[29] <Warning>: MyApp[3096] has active assertions beyond permitted time:
{(
<BKProcessAssertion: 0x14680c60> identifier: Called by MyApp, from -[AppDelegate applicationDidEnterBackground:] process: MyApp[3096] permittedBackgroundDuration: 180.000000 reason: finishTask owner pid:3096 preventSuspend preventIdleSleep preventSuspendOnSleep
)}
翻看其他questions我发现崩溃消息表明我没有正确结束任务,所以当它的时间到期时,操作系统结束它并使我的应用程序崩溃。
所以我添加了一些 NSLogs:
- (void)applicationDidEnterBackground:(UIApplication *)application
{
[self saveContext];
[Settings setCallLock:YES];
[self saveStuff];
if ([self isBackgroundTaskNeeded])
{
UIApplication* app = [UIApplication sharedApplication];
bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
[self pauseDownloads];
NSLog(@"Debug - Ending background task %d",bgTask);
[app endBackgroundTask:bgTask];
NSLog(@"Debug - Background task %d ended",bgTask);
bgTask = UIBackgroundTaskInvalid;
}];
NSLog(@"Debug - Starting background task %d",bgTask);
[self initBackground];
}
}
并发现任务在崩溃时被调用了两次:
Nov 7 12:30:02 iPad MyApp[3096] <Warning>: Debug - Starting background task 7
Nov 7 12:30:30 iPad MyApp[3096] <Warning>: Debug - Starting background task 8
Nov 7 12:33:26 iPad MyApp[3096] <Warning>: Debug - Ending background task 8
Nov 7 12:33:26 iPad MyApp[3096] <Warning>: Debug - Background task 8 ended
Nov 7 12:33:26 iPad MyApp[3096] <Warning>: Debug - Ending background task 0
Nov 7 12:33:26 iPad MyApp[3096] <Warning>: Debug - Background task 0 ended
我无法判断双重调用发生的时间和原因。所以问题是为什么任务被调用两次,有没有办法避免它?
编辑:
- (void) pauseDownloads
{
for (AFDownloadRequestOperation *operation in self.operationQueue.operations)
{
if(![operation isPaused])
{
[operation pause];
}
}
}
最佳答案
你应该在没有过期的情况下结束背景..
UIApplication* app = [UIApplication sharedApplication];
bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
[self pauseDownloads];
NSLog(@"Debug - Ending background task %d",bgTask);
[app endBackgroundTask:bgTask];
NSLog(@"Debug - Background task %d ended",bgTask);
bgTask = UIBackgroundTaskInvalid;
}];
NSLog(@"Debug - Starting background task %d",bgTask);
[self initBackground];
NSLog(@"Debug - Ending background task %d without expiration",bgTask);
[app endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
当应用程序进入前台时,将此平衡 endBackgroundTask
调用 -
- (void)applicationWillEnterForeground:(UIApplication *)application
{
if (bgTask != UIBackgroundTaskInvalid) {
NSLog(@"Debug - Ending background task %d without expiration (when applicationWillEnterForeground)",bgTask);
[app endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}
// Also, to counter expiration handler pauseDownloads call, consider resuming the downloads here (or applicationDidBecomeActive app delegate).
}
因为 - 过期处理程序 block {} 在后台任务过期时执行(通常最多 10 分钟,但不保证)。我假设您的实际后台任务是 [self initBackground];
,否则您应该将其放在代码块之外和 endBackgroundTask
调用之前。
(另一个潜在问题)
此外,我现在注意到您的 pauseDownloads 代码,当应用程序进入后台时,您似乎正在使用 NSOperationQueue 执行下载。在这种情况下,请确保在您完成下载或执行过期处理程序之前不会调用 endBackgroundTask
。换句话说,控件不会过早返回,这意味着您可能需要监视这些下载 NSOperation(s)。
关于IOs7 应用程序在后台崩溃,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/19839269/