Question

sorry if this question has already come up but I couldn’t find anything that addressed the specific problem I’m having here.

I’m working in objective-c on iOS and I have declared an NSMutableDictionary instance variable, a property for it, synthesized it, and allocated space for it in my init method:

SettingsViewController.h

@interface SettingsViewController : UITableViewController <UIAlertViewDelegate> {
    NSMutableDictionary *settingsData;
    UISwitch *emailSwitch;
    UISwitch *phoneSwitch;
    NSMutableData *receivedData;
}

@property (nonatomic, retain) NSMutableDictionary *settingsData;
@property (nonatomic, retain) UISwitch *emailSwitch;
@property (nonatomic, retain) UISwitch *phoneSwitch;
@property (nonatomic, retain) NSMutableData *receivedData;

SettingsViewController.m init method

@synthesize settingsData, emailSwitch, phoneSwitch, receivedData;

# the initialization method, where settingsData is allocated
- (id)initWithStyle:(UITableViewStyle)style {
    self = [super initWithStyle:style];
    if (self) {
        self.navigationItem.title = @"Settings";
        [[self navigationItem] setRightBarButtonItem:[[[UIBarButtonItem alloc]     initWithTitle:@"Done" style:UIBarButtonItemStyleDone target:self action:@selector(doneEditing:)] autorelease]];
        settingsData = [[NSMutableDictionary alloc] init];
    }
    return self;
}

The potion of the method in SettingsViewController.m that uses settingsData (it’s just a very simple parser for a block of data formatted key=value&):

NSMutableString *element = [NSMutableString string];
NSMutableString *value = [NSMutableString string];
bool cap_element = true;
char index;
for (int i = 0; i < [response length]; i++) {
    index = [response characterAtIndex:i];
    if (cap_element && index != '=') {
        [element appendFormat:@"%c", index];
        continue; // skip back to the top
    }
    if (index == '=') {
        cap_element = false;
        continue;
    }
    if (!cap_element && index != '&') {
        [value appendFormat:@"%c", index];
        continue;
    }
    if (index == '&') {
        // store the value in the dict and move onto the next element
        # this output is always correct...
        NSLog(@"Key:%@, Value:%@", element, value);
        [self.settingsData setObject:value forKey:element];
        # ...as is this (the value printed above matches the result here)
        NSLog(@"Result:%@", [settingsData objectForKey:element]);
        [value setString:@""];
        [element setString:@""];
        cap_element = true;
    }
    # but this will output an empty string (username prints correctly above)
    NSLog(@"%@", [self.settingsData objectForKey@"username"]);

The first 2 NSLog() comments output as expected, but as soon as I leave the for loop all of the keys remain and their values become empty strings (so output reads username = “” instead of username = “tester”). I would understand this if the dictionary was not initialized, but I take care of that in the init method shown above. What am I missing?

Answer 1

In the dictionary you are storing a reference to the “value” and “element” variables, not a copy. When you set them to empty string:

[value setString:@""];
[element setString:@""];

you also are updating the values in the dictionary as well.

EDIT: To solve, change this line:

[self.settingsData setObject:value forKey:element];

to this to create new strings (stringWithString should give you autoreleased values):

[self.settingsData setObject: [NSString stringWithString: value] forKey: [NSString stringWithString: element]];