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实现基于数组下标的属性访问模式

实现基于数组下标的属性访问模式

作者: 高思阳 | 来源:发表于2019-07-09 16:30 被阅读0次

    在iOS6.0以及OS X10.8之后,Apple引入了一套非正式协议(informal protocol)与Objective-C语法直接绑定。当你实现了这其中的方法之后即可使用数组下标来访问属性元素。

    在Foundation库中,NSArray类实现了- (id)objectAtIndexedSubscript:(NSUInteger)idx方法。因此,我们可以这么来访问数组元素:

    NSArray *arr = @[@100, @200, @300];
    NSNumber *num = arr[0];
    

    上述arr[0]就相当于[arr objectAtIndex:0]。

    而NSMutableArray在基于NSArray的基础上又实现了- (void)setObject:(id)anObject atIndexedSubscript:(NSUInteger)index方法。这样我们可以通过数组下标来读写相应元素,比如:

    NSMutableArray *arr = [NSMutableArray arrayWithArray:@[@100, @200, @300]];
    arr[2] = arr[0];
    

    而NSDictionary类实现了- (id)objectForKeyedSubscript:(id)key方法。这样我们能以数组下标的形式来访问相应键的值。比如:

    NSDictionary *dict = @{@"key" : @"value"};
    NSString *value = dict[@"key"];
    

    而NSMutableDictionary在NSDictionary类的基础上又实现了'- (void)setObject:(id)object forKeyedSubscript:(id < NSCopying >)aKey'方法。这样,我们能以数组下标的方式来读写相应键的值。比如:

    NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithDictionary:@{@"key":"@Hello"}];
    dict[dict[@"key"]] = @"world";
    

    下面我们通过实现这四个方法,自己实现一个能同时使用这四种下标方式访问模式的类。

    #import <Foundation/Foundation.h>
    
    @interface MyContainer : NSObject
    {
    @private
        NSMutableDictionary *mDict;
        NSMutableArray *mArray;
    }
    
    - (void)setObject:(id)object forKeyedSubscript:(id < NSCopying >)aKey;
    - (id)objectForKeyedSubscript:(id)key;
    - (void)setObject:(id)anObject atIndexedSubscript:(NSUInteger)index;
    - (id)objectAtIndexedSubscript:(NSUInteger)idx;
    
    @end
    
    @implementation MyContainer
    
    - (instancetype)init
    {
        self = [super init];
        
        mDict = [[NSMutableDictionary alloc] initWithDictionary:@{@"key1":@"value1", @"key2":@"value2"}];
        
        mArray = [[NSMutableArray alloc] initWithArray:@[@100, @200, @300, @400]];
        
        return self;
    }
    
    - (void)dealloc
    {
        if(mDict != nil)
        {
            [mDict removeAllObjects];
            [mDict release];
            mDict = nil;
        }
        
        if(mArray != nil)
        {
            [mArray removeAllObjects];
            [mArray release];
            mArray = nil;
        }
        
        [super dealloc];
    }
    
    - (void)setObject:(id)object forKeyedSubscript:(id < NSCopying >)aKey
    {
        [mDict setObject:object forKey:aKey];
    }
    
    - (id)objectForKeyedSubscript:(id)key
    {
        return [mDict objectForKey:key];
    }
    
    - (void)setObject:(id)anObject atIndexedSubscript:(NSUInteger)index
    {
        const NSUInteger length = [mArray count];
        if(index > length)
            return;
        
        if(index == length)
            [mArray addObject:anObject];
        else
            [mArray replaceObjectAtIndex:index withObject:anObject];
    }
    
    - (id)objectAtIndexedSubscript:(NSUInteger)idx
    {
        if(idx >= [mArray count])
            return nil;
        
        return [mArray objectAtIndex:idx];
    }
    
    @end
    
    
    int main (int argc, const char * argv[])
    {
        @autoreleasepool
        {
            // insert code here...
            
            MyContainer *cont = [[MyContainer alloc] init];
            
            cont[@"mykey"] = @"myvalye";
            
            NSLog(@"key1 is: %@", cont[@"key1"]);
            NSLog(@"key2 is: %@", cont[@"key2"]);
            NSLog(@"mykey is: %@", cont[@"mykey"]);
            
            cont[4] = @500;
            cont[2] = @-300;
            
            NSLog(@"The value[4] = %@", cont[4]);
            NSLog(@"The value[3] = %@", cont[3]);
            NSLog(@"The value[2] = %@", cont[2]);
        }
        
        return 0;
    }
    

    https://www.cnblogs.com/zenny-chen/p/3593660.html

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