使用Xcode进行模拟时,PerformFetchWithCompletionHandler调用两次

Question

在Xcode 7.0.1中,"模拟背景"获取命令导致performFetchWithCompletionHandler两次触发.

这是一个Xcode调试错误,还是在运行应用程序发布版本的设备上发生这种情况.

立即更新我们有Xcode 7.1.1,仍然performFetchWithCompletionHandler被调用两次.由于我不确定这是否也"在野外"发生,如果我的提取动作已经在运行,我将保持状态.

- (void)application:(UIApplication *)application performFetchWithCompletionHandler:(nonnull void (^)(UIBackgroundFetchResult))completionHandler {
    if (self.performingFetch) {
        return completionHandler(UIBackgroundFetchResultNoData);
    }
    self.performingFetch = YES;
    ...
    self.performingFetch = NO;
}

Answer 1

我通过在应用程序委托中声明一个静态布尔值来解决这个问题，然后使用该布尔值来执行一次后台提取

if (!runOnce)
{
    [submission startSubmissionProcessWithCompletetionHandler:^(UIBackgroundFetchResult result){
        NSDate *fetchStart = [NSDate date];

        completionHandler(result);

        NSDate *fetchEnd = [NSDate date];
        NSTimeInterval timeElapsed = [fetchEnd timeIntervalSinceDate:fetchStart];
        NSLog(@"Background Fetch Duration: %f seconds", timeElapsed);
    }];
    runOnce = YES;
}
else
{
    completionHandler(UIBackgroundFetchResultNoData);
    runOnce = NO;
}