表达式不可分配，坐标属性来自MKAnnotation类委托 [英] Expression is not assignable, coordinate attribute from MKAnnotation class delegate

问题描述

我这样做是为了更好地解释我的烦恼。

I did this schema in order to explain better what is my troubles.

那么，我该如何解决呢？谢谢=）

So, what can I do to fix it? Thank you =)

推荐答案

CLLocationCoordinate2D c> struct ，即值类型。它通过价值传递，这是另一种说法复制的方式。如果您指定其栏位（例如经度），则只需修改副本;您的注释中的原始坐标将保持不变。

The CLLocationCoordinate2D is a struct, i.e. a value type. It is passed around by value, which is another way of saying "copying". If you assign its fields (e.g. longitude) all that would do is modifying a copy; the original coordinate inside your Annotation would remain intact. That is why the property is not assignable.

要修复此问题，您应该为纬度和经度添加单独的属性，并改为使用：

To fix this, you should add separate properties for latitude and longitude, and use them instead:

@interface Annotation : NSObject<MKAnnotation>
    @property (readwrite) CLLocationDegrees latitude;
    @property (readwrite) CLLocationDegrees longitude;
    @property (nonatomic,assign) CLLocationCoordinate2D coordinate;
    ...
@end

@implementation Annotation
    -(CLLocationDegrees) latitude {
        return _coordinate.latitude;
    }
    -(void)setLatitude:(CLLocationDegrees)val {
        _coordinate.latitude = val;
    }
    -(CLLocationDegrees) longitude{
        return _coordinate.longitude;
    }
    -(void)setLongitude:(CLLocationDegrees)val {
        _coordinate.longitude = val;
    }
@end

现在您的XML解析器代码可以： / p>

Now your XML parser code can do this:

if ([llave isEqualTo:@"lat"]) {
    puntoXML.latitude = [valor doubleValue];
} else if ([llave isEqualTo:@"lon"]) {
    puntoXML.longitude = [valor doubleValue];
} ...

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