iPhone 3.0 指南针：如何获取航向？
我对 Objective-C 比较陌生，而且还不太了解它，所以我对这个可能非常业余的问题表示歉意。
我正在尝试从 CLHeading 和 CLLocationDirection 获取磁航向。 但是，我收到这行代码的编译错误：
locationLabel.text = [[[location course] magneticHeading] stringValue];
错误是：
warning: invalid receiver type 'CLLocationDirection'
error: cannot convert to a pointer type
我真的不明白我在这里做错了什么。 请帮忙！
I'm relatively new to Objective-C and really don't know much about it yet, so I apologise for what is probably a really amateurish question.
I'm trying to get the magnetic heading from CLHeading and CLLocationDirection. However I'm getting compile errors for this line of code:
locationLabel.text = [[[location course] magneticHeading] stringValue];
The errors are:
warning: invalid receiver type 'CLLocationDirection'
error: cannot convert to a pointer type
I don't really understand what I'm doing wrong here. Please help!
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以下是使用指南针所需的步骤。
1）检查可用性：如果位置管理器的
headingAvailable属性为YES，则可以使用指南针。2) 使用位置管理器方法
-(void) startUpdatingHeading开始接收您正在搜索的信息3) 使用委托方法实际检索此信息（不要忘记将自己设置为委托）
希望这有帮助。
Here are the steps needed to use the compass.
1) check the availability: if the
headingAvailableproperty of the location manager is YES, then you can use the compass.2) use the location manager method
-(void) startUpdatingHeadingto begin receiving the information you are searching for3) actually retrieve this information using the delegate method (do not forget to set yourself as the delegate)
Hope this helps.
MagneticHeading 是 CLLocationDirection 类型，它只是基本数据类型“double”的 typedef。 在您的示例中，您尝试向非对象的对象发送消息！ 您应该像这样简单地格式化双精度数：
locationLabel.text = [NSString stringWithFormat:@"Heading %.3f", [[location course]MagneticHeading]];magneticHeading is of CLLocationDirection type, which is simply a typedef for the primitive data type "double". In your example you are trying to send a message to something that is not an object ! You should simply format the double like so:
locationLabel.text = [NSString stringWithFormat:@"Heading %.3f", [[location course] magneticHeading]];您如何分配和初始化
位置？ 确保location定义为(CLLocationDirection *)而不仅仅是(CLLocationDirection)。How are you allocating and initializing
location? Make surelocationis defined as a(CLLocationDirection *)and not just a(CLLocationDirection).