CODEWITHSUNDEEP
iosobjective-cxcodensmutabledictionary
user2105624
user2105624

Reputation: 85

Can't get NSMutableDictionary to work (xcode)

My Objective-C experience is not good, I would love if someone can help with this.

There are some other code around but I believe I simplified this to just the problem. What I am trying to do is to save a double (packed to NSNumber) with a key, below is my code:

.h

@interface MyClass : something
{
    MyMap* usemap;
}
@end

@interface MyMap : something
@property (atomic, strong) NSMutableDictionary* mmap;
@end

.m

@implementation MyMap
@class MyClass;
NSMutableDictionary* mmap = [[NSMutableDictionary alloc] init];
@end

@implementation MyClass
MyMap* usemap = [MyMap alloc];

//-void { switch() { case x:
NSString* key = @"testkey";
NSNumber* value = [NSNumber numberWithDouble:1];
NSLog(@"Saving value: %@ to key: %@",value,key);
[usemap.mmap setObject:value forKey:key];
NSNumber* get = [usemap.mmap objectForKey:key];
NSLog(@"Saved value: %@ to key: %@",get,key);

Now this prints:

Saving value: 1 to key: testkey

Saved value: (null) to key: testkey

What am I missing? it should have saved the double number '1'.

Upvotes: 0

Views: 64

Answers (3)

Bilawal Baig
Bilawal Baig

Reputation: 332

You need to override MyClass init method and initialize MyMap in it usemap = [[MyMap alloc] init]. Then override MyMap init method and initialize mmap in it self.mmap = [[NSMutableDictionary alloc] init].

Do rest of the work in MyClass overridden init method. Here's a rough sketch:

.h

@interface MyClass : something
{
    MyMap* usemap;
}
@end

@interface MyMap : something
@property (atomic, strong) NSMutableDictionary* mmap;
@end

.m

@implementation MyMap
@class MyClass;

- (instancetype)init {
    if ((self = [super init]))
        self.mmap = [[NSMutableDictionary alloc] init];

    return self;
}

@end

@implementation MyClass

- (instancetype)init {

        if ((self = [super init]))
        {
              usemap = [[MyMap alloc] init];

              NSString* key = @"testkey";
              NSNumber* value = [NSNumber numberWithDouble:1];
              NSLog(@"Saving value: %@ to key: %@",value,key);
              [usemap.mmap setObject:value forKey:key];
              NSNumber* get = [usemap.mmap objectForKey:key];
              NSLog(@"Saved value: %@ to key: %@",get,key);
       }

   return self;
}
@end

Hope it helps!

Upvotes: 1

Jeffery Thomas
Jeffery Thomas

Reputation: 42588

Setting up the internals of a object is done with an -init method.

@implementation MyMap
@class MyClass;
// NO NO NO! don't even ask what this does
// NSMutableDictionary* mmap = [[NSMutableDictionary alloc] init];

// YES: Use -init to setup the initial state of an object.
- (instancetype)init {
    self = [super init];
    if (self != nil) {
        // NOTE: _mmap is the instance variable for the property self.mmap.
        _mmap = [[NSMutableDictionary alloc] init];
    }
    return self;
}
@end

Upvotes: 0

aircraft
aircraft

Reputation: 26876

Try this:

MyMap.h:

#import <UIKit/UIKit.h>

@interface MyMap : NSObject
@property (atomic, strong) NSMutableDictionary* mmap;
@end

MyMap.m:

#import "MyMap.h"

@interface MyMap ()

@end

@implementation MyMap

@end

ViewController.m:

MyMap *usemap = [[MyMap alloc] init];
usemap.mmap = [[NSMutableDictionary alloc] init];

NSString* key = @"testkey";
NSNumber* value = [NSNumber numberWithDouble:1];
NSLog(@"Saving value: %@ to key: %@",value,key);
[usemap.mmap setObject:value forKey:key];
NSNumber* get = [usemap.mmap objectForKey:key];
NSLog(@"Saved value: %@ to key: %@",get,key);

The result:

2017-01-21 20:48:59.563 TestOC[4161:50263] Saving value: 1 to key: testkey
2017-01-21 20:48:59.564 TestOC[4161:50263] Saved value: 1 to key: testkey

Upvotes: 0

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