CODEWITHSUNDEEP
objective-ciosjson
mnort9
mnort9

Reputation: 1820

Accessing JSON Data in Objective C

I've downloaded my JSON Data, but I'm having trouble accessing a specific object. From my JSON data, I'm trying to pull the most recent value from variableName = "Elevation of reservoir water surface above datum, ft";

Here is my code:

- (void)viewWillAppear:(BOOL)animated {
[super viewDidAppear:animated];

NSURL *url = [NSURL URLWithString:@"http://waterservices.usgs.gov/nwis/iv/?sites=02334400&period=P7D&format=json"]; 

NSData *jsonData = [NSData dataWithContentsOfURL:url];
if (jsonData != nil) {
    NSError *error = nil;

    id result = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error: &error];

    if (error == nil)
        NSLog(@"%@", result);
}
}

Edited: It's too much data to print the output, but here is how I access the object in JS. I can't seem to write a working for statement that will do the same in Obj-C:

 var d = JSON.parse(responseText);
    for (var i = 0; i < d.value.timeSeries.length; i++) {
        if (d.value.timeSeries[i].variable.variableName == 'Elevation of reservoir      water surface above datum, ft') {
            var result = d.value.timeSeries[i].values[0].value[d.value.timeSeries[i].values[0].value.length - 1];
            console.log(result);
        }

Upvotes: 0

Views: 1567

Answers (2)

Rexeisen
Rexeisen

Reputation: 236

One thing that you may consider is using a tool to generate model classes for you. That way you can use dot accessors to make your life a little bit easier. In the Mac App Store JSON Accelerator or Objectify are pretty good options. You then pipe the NSDictionary into those model classes and it's pretty easy.

Upvotes: 0

Paul.s
Paul.s

Reputation: 38728

This is pretty ugly but it should give you something to start with:

NSArray *timeSeries = [JSON valueForKeyPath:@"value.timeSeries"];

[timeSeries enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
    NSString *variableName = [obj valueForKeyPath:@"variable.variableName"];

    if ([variableName isEqualToString:@"Elevation of reservoir water surface above datum, ft"]) {

        NSArray      *values = [obj valueForKey:@"values"];
        NSDictionary *value  = [values objectAtIndex:0];

        values = [value objectForKey:@"value"];
        value  = [values lastObject];

        NSLog(@"%@", [value objectForKey:@"value"]);
    }
}];

Note

There is no validation/range checking of any kind I'll leave that as an exercise for you to do

Upvotes: 2

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