Dynamically reference variables/objects/arrays etc - ios

Question

This seems such an easy task, at least it is in VB.net. I simply need to reference an array based on a string that is passed to a method. When a view controller loads a method is called and a string is passed. A URL will be created based on this string and JSON will be fetched from it. What I want is for the method to populate an appropriate array based on this passed string.
Here we see the method "goGetData" being called in class "getData" with one of three string parameters "workshop/speaker/exhibitor":
- (void)viewDidLoad
{
[getData goGetData:#"workshop"];
[getData goGetData:#"speaker"];
[getData goGetData:#"exhibitor"];
getData *getDataInstance = [[getData alloc] init];
NSArray *newTablesArray = getDataInstance.jsonAllTables;
NSLog(#"Json currently = %#", newTablesArray);
[super viewDidLoad];
[[self myTableView]setDelegate:self];
[[self myTableView]setDataSource:self];
arrayTable =[[NSMutableArray alloc]init];
}
For example if "goGetDate" is fired with "speaker" I would need the speaker data to be fetched and then the "_jsonSpeaker" array to be populated. Here is my attempt so far to reference and populate the arrays based on what string was passed in the method call:
#import "getData.h"
#implementation getData
+(void)goGetData:(NSString *)requestedTable
{
getData *getDataInstance = [[getData alloc] init];
[getDataInstance buildArray];
[getDataInstance fetchData:requestedTable];
}
-(void)buildArray{
// I tried putting the arrays in an array but still do no know how to reference them
_jsonAllTables = [[NSMutableArray alloc] initWithObjects:_jsonExhibitor, _jsonSpeaker, _jsonWorkshop, nil];
}
-(void)fetchData:(NSString *)requestedTable{
NSString *varCurrentTable;
varCurrentTable = [NSString stringWithFormat:#"_json%#", requestedTable];
NSString *requestedURL;
requestedURL = [NSString stringWithFormat:#"http://testapi.website.com/api/%#", requestedTable];
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:requestedURL]];
[NSURLConnection sendAsynchronousRequest:request queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
{
if (response){
NSHTTPURLResponse *newResp = (NSHTTPURLResponse*)response;
if (newResp.statusCode == 200) {
// STUFF FOR TESTING NSLog(#"Response to request: %# is: %i GOOD", requestedURL, newResp.statusCode);
if ([data length] >0 && error == nil)
{
// STUFF FOR TESTING NSUInteger indexOfArray = [_jsonAllTables indexOfObject:varCurrentTable];
// STUFF FOR TESTING NSString *objectAtIndexOfArray = [_jsonAllTables objectAtIndex:indexOfArray];
// This is the part I think I am stuck on:
// "CURRENT TABLE TO BE POPULATED" = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];
}
else if ([data length] == 0 && error == nil)
{
NSLog(#"Nothing was downloaded");
}
else if (error != nil)
{
NSLog(#"Error: %#", error);
}
} else if (newResp.statusCode == 404){
NSLog(#"Response to request: %# is: %i BAD - URL incorrect", requestedURL, newResp.statusCode);
} else {
// add more returned status error handling here
}
}else{
NSLog(#"No response received");
}
}];
}
#end
Thanks,
Added for clarification on what I am trying to achieve: To save a LOT of writing out the same thing over and over is the following possibly in Obj-c (please excuse the mish-mash of languages)
NSArray *ListOfTables = [NSArray arrayWithObjects:#"Speaker", #"Exhibitor", #"Workshop", nil];
For i as int = 0 to ListOfTables.count{
[self fetchData:(ListOfTables.objectAtIndex = i) withCompletion:^(NSArray* objects, NSError*error){
dispatch_async(dispatch_get_main_queue(), ^{
if (objects) {
self.(ListOfTables.objectAtIndex = i) = objects;
}
else {
NSLog(#"Error: %error", error);
}
});
}];
i++;
Next
};
Notice i don't call a separate method for each table, instead I call the same method but with different table name parameter each time. I can't seem to find a working example with such placeholders in Xcode.

Answer 1

You probably want a method which is asynchronous and returns the result via a completion handler:
typedef void(^completion_t)(NSArray* objects, NSError*error);
-(void)fetchData:(NSString *)tableName
withCompletion:(completion_t)completionHandler;
Usage:
- (void) foo {
[self fetchData:tableName1 withCompletion:^(NSArray* objects, NSError*error){
dispatch_async(dispatch_get_main_queue(), ^{
if (objects) {
self.table1 = objects;
}
else {
NSLog(#"Error: %error", error);
}
});
}];
[self fetchData:tableName2 withCompletion:^(NSArray* objects, NSError*error){
dispatch_async(dispatch_get_main_queue(), ^{
if (objects) {
self.table2 = objects;
}
else {
NSLog(#"Error: %error", error);
}
});
}];
[self fetchData:tableName3 withCompletion:^(NSArray* objects, NSError*error){
dispatch_async(dispatch_get_main_queue(), ^{
if (objects) {
self.table3 = objects;
}
else {
NSLog(#"Error: %error", error);
}
});
}];
}
Implementation:
typedef void(^completion_t)(NSArray* objects, NSError* error);
-(void)fetchData:(NSString *)tableName
withCompletion:(completion_t)completionHandler
{
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:tableName]];
// Setup HTTP headers, e.g. "Accept: application/json", etc.
...
[NSURLConnection sendAsynchronousRequest:request
queue:[[NSOperationQueue alloc] init]
completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
{
NSError* err = error;
NSArray* objects; // final result array as a representation of JSON Array
if (response) {
NSHTTPURLResponse *newResp = (NSHTTPURLResponse*)response;
if (newResp.statusCode == 200) {
if ([data length] >0 && error == nil)
{
NSError* localError;
objects = ... // Use NSJSONSerialization to obtain a representation
if (objects) {
if (completionHandler) {
completionHandler(object, nil);
}
return;
}
else {
err = localError;
}
}
else {
err = ...
}
}
}
if (objects == nil) {
assert(err);
if (completionHandler) {
completionHandler(nil, err);
}
}
}];
}
Asynchronous Loop
Another example, for loading a bunch of data:
First, implemented a method which is an "asynchronous loop":
typedef void(^completion_t)(id result, NSError* error);
- (void) fetchObjectsWithTableNames:(NSMutableArray*)tableNames
completion:(completion_t)completionHandler;
This method is, itself asynchronous, thus the completion handler.
Usage:
- (void) foo
{
NSArray* tableNames = #[#"A", #"B", #"C"]; // possibly 1000
[self fetchObjectsWithTableNames:[tableNames mutableCopy]:^(id result, NSError*error){
if (error) {
NSLog(#"Error: %#", error);
}
else {
// finished fetching a bunch of datas with result:
NSLog(#"Result: %#", result);
}
}];
}
Implementation
- (void) fetchObjectsWithTableNames:(NSMutableArray*)tableNames
completion:(completion_t)completionHandler;
{
if ([tableNames count] > 0) {
NSString* name = [tableNames firstObject];
[tableNames removeObjectAtIndex:0];
[self fetchData:name withCompletion:^(NSArray* objects, NSError*error){
if (objects) {
[self.tables addObject:objects];
[self fetchObjectsWithTableNames:tableNames completion:completionHandler];
}
else {
// handle error
}
}];
}
else {
// finished
if (completionHandler) {
completionHandler(#"finished", nil);
}
}
}