EXC_BAD_ACCESS 崩溃：self.x 与 _x
下面的代码不会
- (void) locationManager:(CLLocationManager *)manager didUpdateHeading:(CLHeading *)newHeading
{
_heading = newHeading.trueHeading;
NSLog(@"heading - %.2f", newHeading.trueHeading);
//NSLog(@"Updating heading - %f", newHeading.trueHeading);
}
像这个那样
- (void) locationManager:(CLLocationManager *)manager didUpdateHeading:(CLHeading *)newHeading
{
self.heading = newHeading.trueHeading;
NSLog(@"heading - %.2f", newHeading.trueHeading);
//NSLog(@"Updating heading - %f", newHeading.trueHeading);
}
崩溃有人可以解释为什么会出现这种情况吗？该属性看起来像：
@property (nonatomic, assign) float heading;
而且它永远不会在 init 方法中初始化，因为我不想存储一个值，直到它正确为止。现在是：
- (id) initUser
{
return [self init];
}
The following code does not crash
- (void) locationManager:(CLLocationManager *)manager didUpdateHeading:(CLHeading *)newHeading
{
_heading = newHeading.trueHeading;
NSLog(@"heading - %.2f", newHeading.trueHeading);
//NSLog(@"Updating heading - %f", newHeading.trueHeading);
}
where as this one does
- (void) locationManager:(CLLocationManager *)manager didUpdateHeading:(CLHeading *)newHeading
{
self.heading = newHeading.trueHeading;
NSLog(@"heading - %.2f", newHeading.trueHeading);
//NSLog(@"Updating heading - %f", newHeading.trueHeading);
}
Can someone explain why this is the case? The property looks like:
@property (nonatomic, assign) float heading;
Also it is never initialized in the init method because I don't want to store a value until it is right. Right now it is:
- (id) initUser
{
return [self init];
}
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声明属性后，应使用 @synthesize 告诉编译器生成 getter 和 setter 方法。默认情况下，这些方法被命名为 foo 和 setFoo，其中 foo 是变量的名称。另外，默认情况下，属性表示的变量与属性具有相同的名称，除非您使用 @synthesize foo=_foo 更改此名称以使用不同的命名实例变量。
After you declare a property, you should use
@synthesizeto tell the compiler to generate a getter and setter method. By default, these methods are named foo and setFoo, where foo is a name of the variable. Also, by default, the variable represented by the property has the same name as a property, unless you change this with @synthesize foo=_foo to use to a different named instance variable.