Check ALAssetsLibrary empty or not - iphone

Question

I am using ALAssetsLibrary and app getting crashed when it is empty.How do i check whether it is empty or not?.
-(void)getLastImageName1
{
// if (val < 10) {
// NSLog(#"getLastImageName1\n");
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
// Enumerate just the photos and videos group by using ALAssetsGroupSavedPhotos.
last =1;
[library enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
// Within the group enumeration block, filter to enumerate just photos.
[group setAssetsFilter:[ALAssetsFilter allPhotos]];
if (last == 1) {
// NSLog(#"last\n");
last++;
// Chooses the photo at the last index
[group enumerateAssetsAtIndexes:[NSIndexSet indexSetWithIndex:[group numberOfAssets]-1] options:0 usingBlock:^(ALAsset *alAsset, NSUInteger index, BOOL *innerStop) {
// The end of the enumeration is signaled by asset == nil.
if (alAsset) {
NSString *lastImgNew = alAsset.defaultRepresentation.filename;
// NSLog(#"current img name %#\n",lastImgNew);
NSString *plistPath1 = [DOCUMENT_DIR_PATH stringByAppendingPathComponent:#"previouslastimagename.plist"];
NSArray *lastImg = [NSArray arrayWithContentsOfFile:plistPath1];
// NSLog(#"get pre lastimg %#\n",lastImg);
// NSArray *lastImg = [[DBModel database]getPreviousName];
// NSLog(#"get lastImg %#\n",lastImg);
if ([lastImg count] != 0) {
// NSLog(#"count\n");
if ([[lastImg objectAtIndex:0] isEqualToString:lastImgNew]) {
// NSLog(#"img eql\n");
// UIAlertView *alert = [[UIAlertView alloc]initWithTitle:#"" message:#"equal" delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil, nil];
// [alert show];
[self hideImage];
// }
}
else
{
// UIAlertView *alert = [[UIAlertView alloc]initWithTitle:#"" message:[NSString stringWithFormat:#"pre %# current %#",[lastImg objectAtIndex:0],lastImgNew] delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil, nil];
// [alert show];
// NSLog(#"img not eql\n");
[self performSelectorOnMainThread:#selector(displayAlert) withObject:nil waitUntilDone:YES];
}
}
}
}];
}
} failureBlock: ^(NSError *error) {
// Typically you should handle an error more gracefully than this.
// NSLog(#"No groups");
}];
The line which after last++ variable.I am checking lastimage with newscreenshot image to not allow user to use app after taking screenshot

Answer 1

This is the line that is giving you the error:
[NSIndexSet indexSetWithIndex:[group numberOfAssets]-1]
If there are zero assets then you are setting the index to -1. You can wrap that enum block in a conditional to test if numberOfAssets > 0 before proceeding. Also, there are other questions you may find helpful to look at here. Ex.: How to get the latest photo in iPhone Library?