无法让 NSMutableDictionary 工作 (xcode)

Question

我的 Objective-C 体验不好，如果有人可以帮助我，我会很高兴。

周围还有一些其他代码，但我相信我已将其简化为问题所在。我想做的是用一个键保存一个双精度数（打包到 NSNumber），下面是我的代码：

.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);

现在打印：

Saving value: 1 to key: testkey

Saved value: (null) to key: testkey

我错过了什么？它应该保存双数“1”。

Answer 1

试试这个：

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);

结果：

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

Answer 2

您需要覆盖 MyClass init 方法并在其中初始化 MyMap usemap = [[MyMap alloc] init]。然后覆盖 MyMap init 方法并在其中初始化 mmap self.mmap = [[NSMutableDictionary alloc] init].

在 MyClass 覆盖的 init 方法中完成其余工作。这是一个粗略的草图：

.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

希望对您有所帮助！

Answer 3

设置对象的内部结构是使用 -init 方法完成的。

@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

无法让 NSMutableDictionary 工作 (xcode)

Can't get NSMutableDictionary to work (xcode)

xcode

objective-c

nsmutabledictionary

ios