In my case, I need to query from 3 map layers and get non-graphic information data and display them in 3 table lists.
I tried to use NSOperationQueue to manage
- (NSOperation *)executeWithQuery:(AGSQuery *)query;
But this returned NSOperation is already running, thus cannot be added to NSOperationQueue.
Below is how I roughly achieved but I really think it's a bad practice, because for this case I created 3 booleans and 3 AGSQueryTasks for 3 queries, and more variables will be needed if need to query from more layers.
I hope you guys can have a better way to introduce.
@interface MultipleQueryTest () <AGSQueryTaskDelegate>
{
BOOL _multipleQueryStart;
BOOL _flagQueryOperationAComplete;
BOOL _flagQueryOperationBComplete;
BOOL _flagQueryOperationCComplete;
AGSQueryTask *_queryTaskA;
AGSQueryTask *_queryTaskB;
AGSQueryTask *_queryTaskC;
NSArray *_resultA;
NSArray *_resultB;
NSArray *_resultC;
}
@end
@implementation MultipleQueryTest
- (IBAction)btnGoTapped:(id)sender
{
_multipleQueryStart = YES;
// query A
NSURL *layerAURL = [self getURLForLayer: eLayerA];
NSArray *outFieldsA = [NSArray arrayWithObjects:@field1, @field2, ... nil];
NSOperation *queryOpA = [self startQuyerOperationWithURL:layerAURL outFields:outFieldsA operationType:eOperationTypeA];
quryOpA.name = @operationA;
_flagQueryOperationACompleted = NO;
// query B
NSURL *layerBURL = [self getURLForLayer: eLayerB];
NSArray *outFieldsB = [NSArray arrayWithObjects:@field1, @field2, ... nil];
NSOperation *queryOpB = [self startQuyerOperationWithURL:layerBURL outFields:outFieldsB operationType:eOperationTypeB];
quryOpB.name = @operationB;
_flagQueryOperationBCompleted = NO;
// query C
NSURL *layerCURL = [self getURLForLayer: eLayerC];
NSArray *outFieldsC = [NSArray arrayWithObjects:@field1, @field2, ... nil];
NSOperation *queryOpC = [self startQuyerOperationWithURL:layerCURL outFields:outFieldsC operationType:eOperationTypeC];
quryOpC.name = @operationC;
_flagQueryOperationCCompleted = NO;
}
- (NSOperation *)startQuyerOperationWithURL:(NSURL *)layerURL outFields:(NSArray *)outFields operationType:(eOperationType)opType
{
AGSQuery *query = [AGSQuery query];
query.outSpatialReference = self.mapView.spatialReference;
query.outFields = outFields;
query.returnGeometry = NO;
AGSQueryTask queryTaskObj = [[AGSQueryTask alloc] initWithURL: layerURL];
queryTaskObj.delegate = self;
if (opType == eOperationTypeA)
{
_queryTaskA = queryTaskObj;
return [_queryTaskA executeWithQuery:query];
}
else if (opType == eOperationTypeB)
{
_queryTaskB = queryTaskObj;
return [_queryTaskB executeWithQuery:query];
}
else if (opType == eOperationTypeC)
{
_queryTaskC = queryTaskObj;
return [_queryTaskC executeWithQuery:query];
}
else
return nil;
}
#pragma mark - AGSQueryTaskDelegate
- (void)queryTask:(AGSQueryTask *)queryTask operation:(NSOperation *)op didExecuteWithFeatureSetResult:(AGSFeatureSet *)featureSet
{
if (_multipleQueryStart)
{
if ([op.name isEqualToString:@operationA]) {
_resultA = featureSet.features;
_flagQueryOperationACompleted = YES;
_queryTaskA = nil;
}
else if ([op.name isEqualToString:@operationB]) {
_resultB = featureSet.features;
_flagQueryOperationBCompleted = YES;
_queryTaskB = nil;
}
else if ([op.name isEqualToString:@operationC]) {
_resultC = featureSet.features;
_flagQueryOperationCCompleted = YES;
_queryTaskC = nil;
}
if (_flagQueryOperationACompleted && _flagQueryOperationBCompleted && _flagQueryOperationCCompleted)
{
NSLog(@All list received.......);
_multipleQueryStart = NO;
}
return;
@}
}
@end
