iOS 学习笔记4－NSDictionary 和 NSMutableDictionary

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       /*        字典：        存储的内存不是连续的，         key－value 对应，        */// 创建方法：        // 1.不常用，只有一组k－v        NSDictionary* dict1 = [NSDictionary dictionaryWithObject:@"1" forKey:@"a"];        NSLog(@"dict1 = %@", dict1);        // 2. 创建多个        NSDictionary* dict2 = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"1", @"2",@"3", nil] forKeys:[NSArray arrayWithObjects:@"a", @"b", @"c", nil]];        NSLog(@"dict2 = %@", dict2);                // 3. ios5以后的简便写法        NSDictionary* dict3 = @{@"a":@"1", @"b":@"2"};        NSLog(@"dict3 = %@", dict3);// 常用方法        // count        int count = [dict2 count];        NSLog(@"count = %d", count);                // key, value查找        NSString* value = [dict2 valueForKey:@"b"];        NSLog(@"value for b is %@", value);                NSString* value2 =  [dict2 objectForKey:@"b"];        NSLog(@"value2 for b is %@", value2);                        NSArray* allValues = [dict2 allValues];        NSLog(@"all values is %@", allValues);                        NSArray* allKeys= [dict2 allKeys];        NSLog(@"all keys are is %@", allKeys);                NSArray* array = [dict2 objectsForKeys:[NSArray arrayWithObjects:@"a", @"b", @"d", nil] notFoundMarker:@"Not Found"];        NSLog(@"array is %@", array);        //遍历字典        // for in 快速遍历        for(NSString* str in dict2){            NSLog(@"the key is %@, the value is %@", str, dict2[str]);        }        //2. 枚举器遍历        NSEnumerator* en = [dict2 keyEnumerator];        id key = nil;        while(key = [en nextObject]){            NSLog(@"key - %@", key);                    } //NSMutableDictionary        // 1. 添加        NSMutableDictionary* dict4 = [[NSMutableDictionary alloc] init]; // 不需要初始赋值，因为可以随时添加        [dict4 setObject:@"1" forKey:@"a"];        [dict4 setObject:@"2" forKey:@"b"];        [dict4 setObject:@"3" forKey:@"c"];        [dict4 setObject:@"4" forKey:@"d"];        // 2. 删除        [dict4 removeObjectForKey:@"a"];                [dict4 removeObjectsForKeys: [NSArray arrayWithObjects:@"a",@"b", nil]];                [dict4 removeAllObjects];
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