Whenever early versions of the AWS SDK for iOS encountered an error, they threw either an AmazonServerException or an AmazonClientException. This forced developers to surround any AWS-related code with @try/@catch blocks. This was not intuitive for many Objective-C developers and is not the recommended way to handle error conditions in the Cocoa Framework. Starting with the AWS SDK for iOS version 1.4.0, we introduced a new option to return NSError objects instead of throwing exceptions.

Turning Off the Exceptions

You can enable this option by importing AmazonErrorHandler.h and calling [AmazonErrorHandler shouldNotThrowExceptions]. We recommend that you make this call in the application:didFinishLaunchingWithOptions: application delegate method. Once this method is invoked, the error property in the AmazonResponse object contains an NSError object for any failed calls to AWS.

#import "AppDelegate.h"
#import <AWSiOSSDK/AmazonErrorHandler.h>

@implementation AppDelegate

-(BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    ...
    [AmazonErrorHandler shouldNotThrowExceptions];
    ...

Handling the Errors

Always confirm that the error property is nil before continuing.

S3GetObjectRequest  *getObjectRequest  = [[[S3GetObjectRequest alloc] initWithKey:YOUR_OBJECT_KEY withBucket:YOUR_BUCKET_NAME] autorelease];
S3GetObjectResponse *getObjectResponse = [s3Client getObject:getObjectRequest];
if(getObjectResponse.error != nil)
{
    NSLog(@"Error: %@", getObjectResponse.error);
    return;
}

// Do something with getObjectResponse.

For asynchronous calls with AmazonServiceRequestDelegate, the request:didFailWithError: delegate method is called instead of request:didFailWithServiceException:. Only one delegate method will be called in the case of error, never both. The delegate method called will match the kind of error behavior you desire: exceptions or errors.

-(void)request:(AmazonServiceRequest *)request didFailWithError:(NSError *)theError
{
    // Do something with theError.
}

-(void)request:(AmazonServiceRequest *)request didFailWithServiceException:(AmazonServiceException *)theException
{
    // This delegate method won't be called anymore. You can remove this delegate method from your apps.
}

Keeping the Exceptions

Today, the default behavior of the AWS SDK for iOS is to throw exceptions, but we plan to make NSError the default behavior in a future SDK release. If you prefer exceptions, and if you want to ensure that your current code continues to work even after the default behavior changes, call [AmazonErrorHandler shouldThrowExceptions] like so:

#import "AppDelegate.h"
#import <AWSiOSSDK/AmazonErrorHandler.h>

@implementation AppDelegate

-(BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    ...
    [AmazonErrorHandler shouldThrowExceptions];
    ...

All of our sample apps now use errors, so please take a look at any of our new samples for the details on how to handle errors.

As always, please let us know if you have any questions.