创建NSDictionary

Question

在以下代码中，第一个日志语句按预期显示小数，但第二个日志语句为NULL。我做错了什么？

NSDictionary *entry = [[NSDictionary alloc] initWithObjectsAndKeys:
  @"x", [NSNumber numberWithDouble:acceleration.x],
  @"y", [NSNumber numberWithDouble:acceleration.y],
  @"z", [NSNumber numberWithDouble:acceleration.z],
  @"date", [NSDate date],
  nil];
NSLog([NSString stringWithFormat:@"%@", [NSNumber numberWithDouble:acceleration.x]]);
NSLog([NSString stringWithFormat:@"%@", [entry objectForKey:@"x"]]);

Answer 1

您正在交换插入对象和键的顺序：您需要首先插入对象，然后插入键，如下例所示。

NSDictionary *dict = [[NSDictionary alloc] initWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil];

Answer 2

新的Objective-c支持这种静态初始化的新语法。

@{key:value}

例如：

NSDictionary* dict = @{@"x":@(acceleration.x), @"y":@(acceleration.y), @"z":@(acceleration.z), @"date":[NSDate date]};

Answer 3

NSDictionary语法：

NSDictionary *dictionaryName = [NSDictionary dictionaryWithObjectsAndKeys:@"value1",@"key1",@value2",@"key2", nil];

示例：

NSDictionary *importantCapitals = [NSDictionary dictionaryWithObjectsAndKeys:
@"NewDelhi",@"India",@"Tokyo",@"Japan",@"London",@"UnitedKingdom", nil];
NSLog(@"%@", importantCapitals);

输出看起来像，

  

{India = NewDelhi;日本=东京; UnitedKingdom =伦敦; }