创建NSDictionary [英] Creating an NSDictionary

问题描述

在以下代码中，第一个日志语句按预期显示小数，但第二个日志为NULL。

In the following code, the first log statement shows a decimal as expected, but the second logs NULL. What am I doing wrong?

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"]]);

推荐答案

您正在交换插入对象的顺序键：您需要首先插入对象，然后按如下例所示的键。

You are exchanging the order in which you insert objects and key: you need to insert first the object, then the key as shown in the following example.

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

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