when the ALAssetsLibraryGroupsEnumerationResultsBlock function is trigger in ios - ios

Question

In my app i want to get the image and video from particular album.so i use ALAssetsLibraryGroupsEnumerationResultsBlock function for get the images and video from the particular Album.here i store the asset value in a nsmutablearray,i get that array values on viewdidLoad, but in viewdidload the array value is null.So when ALAssetsLibraryGroupsEnumerationResultsBlock is trigger.
Below is my code help me..
- (void)viewDidLoad {
[super viewDidLoad];
if (self.assetLibrary == nil) {
_assetLibrary = [[ALAssetsLibrary alloc] init];
}
if (self.groups == nil) {
_groups = [[NSMutableArray alloc] init];
} else {
[self.groups removeAllObjects];
}
[self loadAssetImages];
}
-(void)loadAssetImages{
NSLog(#"Load asset Image ");
ALAssetsLibraryAccessFailureBlock failureBlock = ^(NSError *error) {
UIAlertView * alert = [[UIAlertView alloc] initWithTitle:#"ERROR" message:[NSString stringWithFormat:#"No Albums Available"] delegate:nil cancelButtonTitle:#"Ok" otherButtonTitles:nil];
[alert show];
};
ALAssetsLibraryGroupsEnumerationResultsBlock listGroupBlock = ^(ALAssetsGroup *group, BOOL *stop) {
NSLog(#"Block");
if (group == nil)
{
return;
}
if ([[group valueForProperty:ALAssetsGroupPropertyName] isEqualToString:#"FlipDemo"]) {
[self.groups addObject:group];
[self loadImages];
return ;
}
if (stop) {
return;
}
};
NSLog(#"Block Out");
[self.assetLibrary enumerateGroupsWithTypes:ALAssetsGroupAll
usingBlock: listGroupBlock
failureBlock:failureBlock];
}
-(void)loadImages{
NSLog(#"Load Image000");
ALAssetsGroup *assetGroup;
for (assetGroup in self.groups)
{
for (int i = 0; i<[self.groups count]; i++)
{
[ assetGroup enumerateAssetsUsingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop)
{
if (result) {
if ([[result valueForProperty:ALAssetPropertyType] isEqualToString:ALAssetTypeVideo])
{
[videoOnly addObject:result];
}
else if ([[result valueForProperty:ALAssetPropertyType] isEqualToString:ALAssetTypePhoto])
{
[imgOnly addObject:result];
// NSLog(#"Photo");
}
}
}
];
}
}
}

Answer 1

The method is asynchronous. You can find the function detail in help document:
help document
(void)enumerateGroupsWithTypes:(ALAssetsGroupType)types
usingBlock:(ALAssetsLibraryGroupsEnumerationResultsBlock)enumerationBlock
failureBlock:(ALAssetsLibraryAccessFailureBlock)failureBlock
This method is asynchronous. When groups are enumerated, the user may be asked to confirm the application's access to the data; the method, though, returns immediately. You should perform whatever work you want with the assets in enumerationBlock.
end of help document
So, according your code, you can't get anything in your main thread. Because iOS get assets in another thread.
You can set a key-value observation to make main thread waiting for this asynchronous function.
1) set a property, for example: handleOverFindFlag
2) before execute the function: set handleOverFindFlag=NO
3) add Observer
[self addObserver:self forKeyPath:#"handleOverFindFlag" options:0 context:NULL];
4) set observing function:
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:
(NSDictionary *)change context:(void *)context
{
if([keyPath isEqualToString:#""])
{
//handle your findings
}
}
5) after doing this
[self removeObserver:self forKeyPath:#"handleOverFindFlag"];
You can find detail about Key-Value coding in help document.