为什么我无法捕获此iOS AWS SDK网络错误？

Question

I'm using the AWS iOS SDK in my app, and I recently tested a no-network situation. This is my code:

dispatch_queue_t Q = dispatch_queue_create("ec2_instance_fetch", NULL);
dispatch_async(Q, ^{
    AmazonEC2Client *client = [[AmazonEC2Client alloc] initWithAccessKey:[ESCredentialsManager accessKey] withSecretKey:[ESCredentialsManager secretKey]];
    client.endpoint = [NSString stringWithFormat:@"https://%@", [ESRegionManager endpointForRegion:[ESRegionManager activeRegionObject]]];
    EC2DescribeInstancesResponse *response = [client describeInstances:[[EC2DescribeInstancesRequest alloc] init]];
    NSMutableArray *temp = @[].mutableCopy;
    for (EC2Reservation *reserv in response.reservations) {
        for (EC2Instance *instance in reserv.instances) {
            [temp addObject:instance];
        }
    }
    self.instances = temp;
    dispatch_async(dispatch_get_main_queue(), ^{
        [self.tableView reloadData];
    });
});

In a no connection situation, it throws this error:

 *** Terminating app due to uncaught exception 'AmazonClientException', reason: 'Error Domain=NSURLErrorDomain Code=-1009 "The Internet connection appears to be offline." UserInfo=0x16e55460 {NSErrorFailingURLStringKey=https://ec2.us-east-1.amazonaws.com/, NSErrorFailingURLKey=https://ec2.us-east-1.amazonaws.com/, NSLocalizedDescription=The Internet connection appears to be offline., NSUnderlyingError=0x16dea2c0 "The Internet connection appears to be offline."}'
*** First throw call stack:
(0x301adf4b 0x3a91c6af 0xbbae1 0xbb31d 0xba6c7 0xba177 0xbd3ab 0xa2bab 0x3adffd1b 0x3ae06273 0x3ae0606b 0x3ae06ce1 0x3ae06f59 0x3af41dbf 0x3af41c84)
libc++abi.dylib: terminating with uncaught exception of type AmazonServiceException
(lldb) 

So I tried to simply catch the error like this:

dispatch_queue_t Q = dispatch_queue_create("ec2_instance_fetch", NULL);
dispatch_async(Q, ^{
    @try {
        AmazonEC2Client *client = [[AmazonEC2Client alloc] initWithAccessKey:[ESCredentialsManager accessKey] withSecretKey:[ESCredentialsManager secretKey]];
        client.endpoint = [NSString stringWithFormat:@"https://%@", [ESRegionManager endpointForRegion:[ESRegionManager activeRegionObject]]];
        EC2DescribeInstancesResponse *response = [client describeInstances:[[EC2DescribeInstancesRequest alloc] init]];
        NSMutableArray *temp = @[].mutableCopy;
        for (EC2Reservation *reserv in response.reservations) {
            for (EC2Instance *instance in reserv.instances) {
                [temp addObject:instance];
            }
        }
        self.instances = temp;
        dispatch_async(dispatch_get_main_queue(), ^{
            [self.tableView reloadData];
        });
    }
    @catch (NSError *error) {
        NSLog(@"Error: %@", error);
    }
});

But it still fails with the same error, and the app crashes. Why can't I catch this error this way? How can I?

Answer 1

Don't catch NSError . Catch NSException .