属性未在iOS 7中初始化 [英] Properties don't get initialized in iOS 7

问题描述

我正在为iOS 7开发，但是我仍然必须手动编写getter，否则我的属性就不会初始化.我试着手动合成那些属性，即使现在不再需要它了，但这也没有实现.

I'm developing for iOS 7 but I still have to manually write getters otherwise my properties just don't get initialized. I tried to manually synthesize those properties, even though that shouldn't be needed anymore, but that doesn't do it.

在下面的视图控制器中，我使用属性motionTracker，该属性从未初始化.我所有的项目都有相同的问题，所以我知道这是我的误解.

In my view controller below, I use the property motionTracker, which never gets initialized. I have the same issue with all my projects, so I know it's a misunderstanding on my part.

#import "ViewController.h"
#import "TracksMotion.h"

@interface ViewController ()

@property (weak, nonatomic) IBOutlet UIButton *startRecording;
@property (weak, nonatomic) IBOutlet UIButton *stopRecording;

@property (strong, nonatomic) TracksMotion *motionTracker;
@end

@implementation ViewController

@synthesize motionTracker = _motionTracker;

- (void)startMyMotionDetect
{
    [self.motionTracker startsTrackingMotion];
}

@end

motionTracker具有用于方法startsTrackingMotion的公共API，所以我不知道为什么这不起作用.

The motionTracker has a public API for the method startsTrackingMotion so I don't know why this doesn't work.

#import <Foundation/Foundation.h>
#import <CoreMotion/CoreMotion.h>

@interface TracksMotion : NSObject

- (void)startsTrackingMotion;

- (void)stopTrackingMotion;

@property (strong, nonatomic) CMMotionManager *motionManager;

@end

推荐答案

属性/实例变量不是为您神奇地初始化的.当你说:

Properties / instance variables are not magically initialized for you. When you say:

@property (strong, nonatomic) TracksMotion *motionTracker;

...您只是为实例变量保留内存空间(并通过@synthesize或自动合成生成getter和setter方法).在您放置之前，这里没有实际的TracksMotion对象.您必须编写代码才能做到这一点.您必须创建或获取 TracksMotion实例，并在某个时候将其分配给self.motionTracker，大概是在self生命周期的早期(在这种情况下，这是一个ViewController实例).在运行执行此操作的代码之前，self.motionTracker为零.

... you are just reserving memory space for an instance variable (and generating a getter and a setter method through @synthesize or autosynthesis). There is no actual TracksMotion object there until you put one there. You must write code to do that. You must create or obtain a TracksMotion instance and assign it to self.motionTracker at some point, presumably early in the life of self (in this case, that's a ViewController instance). Until you run code that does that, self.motionTracker is nil.

((您可能会感到困惑，因为它似乎自动初始化了出口 .例如，您已经获得@property (weak, nonatomic) IBOutlet UIButton *startRecording;并且可以肯定的是，self.startRecording是一个按钮.但是那是因为笔尖加载过程为您做了我要说的必须要做的事情:它从情节提要或.xib文件中创建一个按钮，并将其分配给该实例变量.)

(It is possible that you are being confused because it looks like outlets are automatically initialized. For example, you've got @property (weak, nonatomic) IBOutlet UIButton *startRecording; And sure enough, self.startRecording is a button. But that's because the nib-loading process does for you the very thing I'm saying you must do: it makes a button from the storyboard or .xib file, and assigns it to this instance variable.)

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