cocoa - 使用 NSUserDefaults 存储图像坐标

Question

我正在我的应用程序中移动图像，运行良好。问题是，当用户返回该 View 时，我想将图像保留在适当的位置。目前，我使用字符串来固定图像中心:

NSString *centre = NSStringFromCGPoint(image.center);

我有一个名为 theCentre 的 NSUserDefault 变量:

theCentre = [NSUserDefaults standardUserDefaults];

我尝试使用以下方法保存:

[theCentre setObject:centre forKey:@"centre"];

当我输出日志时，我得到以下内容:

{280, 320}

这太棒了。在 viewDidLoad 中，我尝试了完全相同的日志，它正在返回(null)。我认为这意味着它没有正确保存中心。我是否在这里遗漏了一些基本的东西，因为我在应用程序的其他地方使用了 NSUserDefaults 并且它一直工作正常。非常感谢。
编辑:这是尝试帮助调试的整个代码:)

-(void)getBounds
{
lowerBoundX = 250;
upperBoundX = 310;
lowerBoundY = 290;
upperBoundY = 350;

}

#pragma mark -
#pragma mark UIPanGestureRecognizer selector

- (void) dragGesture:(UIPanGestureRecognizer *) panGesture
{
 [self getBounds];

CGPoint translation = [panGesture translationInView:self.view];

switch (panGesture.state) {
    case UIGestureRecognizerStateBegan:{
        originalCentre = dragImage.center;
    }
        break;
    case UIGestureRecognizerStateChanged:{
        dragImage.center = CGPointMake(dragImage.center.x + translation.x,
                                       dragImage.center.y + translation.y);

    }
        break;
    case UIGestureRecognizerStateEnded:{            
        if (((dragImage.center.x >= lowerBoundX) && (dragImage.center.y >= lowerBoundY) &&
            (dragImage.center.x <= upperBoundX) && (dragImage.center.y <= upperBoundY))) {

            dragImage.center = CGPointMake(280, 320);
            [dragImage setUserInteractionEnabled:NO];

            theCentre = [NSUserDefaults standardUserDefaults];

        NSString *centre = NSStringFromCGPoint(dragImage.center);

            [theCentre setObject:centre forKey:@"centre"];

            NSLog(@"%@", [theCentre objectForKey:@"centre"]);
            [theCentre synchronize];

            break;
        }
        [UIView animateWithDuration:0.5 
                         animations:^{
                             dragImage.center = originalCentre;
                         }
                         completion:^(BOOL finished){
                         }];
    }
        break;
    default:
        break;
}

[panGesture setTranslation:CGPointZero inView:self.view];
}

-(IBAction)clear{
[UIImageView animateWithDuration:0.5 animations:^{
dragImage.center = CGPointMake(100, 200);
}];

[dragImage setUserInteractionEnabled:YES];
}

- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view.

NSLog(@"%@", [theCentre objectForKey:@"centre"]);

UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(dragGesture:)];

[dragImage addGestureRecognizer:panGesture];

[dragImage setUserInteractionEnabled:YES];

}

Answer 1

数据保存在 NSUserDefaults首先被缓存，因此它不能立即从 NSUserDefaults 的其他实例中使用。数据会按照某些预定义的事件/时间间隔定期保存。但是您可以通过调用 synchronize 来强制数据同步。像这样:

NSString *theCenter = NSStringFromCGPoint(image.center);
theCenter = [NSUserDefaults standardUserDefaults];
[theCenter setObject:centre forKey:@"center"];
[theCenter synchronize];