记一种页面loading动画实现套路

一、需求

1. 首次进入这个页面需要有一个loading动画，当首次加载出错时，需要展示一个错误页，点击错误页可以重新加载，重新加载也需要loading动画。

2. 去到下级页面再返回此页面时，需要重新请求数据刷新页面，这次请求数据时不需要loading动画，且请求数据出错时，也不需要展示错误页，页面保持原样。

以上需求，我们如何实现这样的loading动画逻辑呢？

二、实现

直接上代码：

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self setUpUI];
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    //isMovingToParentViewController是iOS 5 之后系统提供的API
    BOOL needLoadingAnimation = self.isMovingToParentViewController;
    [self requestDataAnimated:needLoadingAnimation];
}

- (void)requestDataAnimated:(BOOL)animated
{
    //1.根据animated添加loading动画
    if (animated) {
        [IGPageLoadingView showInPageView:self.view];
    }
    [IGNetworkManager requestWithReq:nil successCallback:^(NSInteger resultCode, NSString *resultMsg, id body) {
        //2.请求成功后移除loading动画
        [IGPageLoadingView removeFromPageView:self.view];
        [self refresh];
    } failedCallback:^(NSInteger resultCode, NSString *resultMsg, id body) {
        //3.请求失败也要移除loading动画
        [IGPageLoadingView removeFromPageView:self.view];
        //4.根据animated添加错误页
        if (animated) {
            [IGPageErrorView showInPageView:self.view tapAction:^{
                [self requestDataAnimated:YES];
            }];
        }
    }];
}

代码解析：

1. 在viewWillAppear中发起请求，这样每一次进入页面都会刷新，再根据isMovingToParentViewController来判断是否为首次进入，首次进入则添加loading动画。

2. 请求数据方法添加animated参数，根据animated来判断是否添加loading动画。

3. 如果是一个简单页面，不需要每次进入都刷新，也不要支持下拉刷新，则loading动画添加方法如下：

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self setUpUI];
    [self requestData];
}

- (void)requestData
{
    //1.添加loading动画
    [IGPageLoadingView showInPageView:self.view];
    [IGNetworkManager requestWithReq:nil successCallback:^(NSInteger resultCode, NSString *resultMsg, id body) {
        //2.请求成功后移除loading动画
        [IGPageLoadingView removeFromPageView:self.view];
        [self refresh];
    } failedCallback:^(NSInteger resultCode, NSString *resultMsg, id body) {
        //3.请求失败添加错误页（添加错误页会自动移除loading动画）
        [IGPageErrorView showInPageView:self.view tapAction:^{
            [self requestData];
        }];
    }];
}

 

三、知识扩展

iOS 5 之后，UIViewController新增以下4个方法：

/*
  These four methods can be used in a view controller's appearance callbacks to determine if it is being
  presented, dismissed, or added or removed as a child view controller. For example, a view controller can
  check if it is disappearing because it was dismissed or popped by asking itself in its viewWillDisappear:
  method by checking the expression ([self isBeingDismissed] || [self isMovingFromParentViewController]).
*/

#if UIKIT_DEFINE_AS_PROPERTIES
@property(nonatomic, readonly, getter=isBeingPresented) BOOL beingPresented NS_AVAILABLE_IOS(5_0);
@property(nonatomic, readonly, getter=isBeingDismissed) BOOL beingDismissed NS_AVAILABLE_IOS(5_0);

@property(nonatomic, readonly, getter=isMovingToParentViewController) BOOL movingToParentViewController NS_AVAILABLE_IOS(5_0);
@property(nonatomic, readonly, getter=isMovingFromParentViewController) BOOL movingFromParentViewController NS_AVAILABLE_IOS(5_0);
#else
- (BOOL)isBeingPresented NS_AVAILABLE_IOS(5_0);
- (BOOL)isBeingDismissed NS_AVAILABLE_IOS(5_0);

- (BOOL)isMovingToParentViewController NS_AVAILABLE_IOS(5_0);
- (BOOL)isMovingFromParentViewController NS_AVAILABLE_IOS(5_0);
#endif

看接口注释能知道，如果通过presentViewController方法弹出的Modal ViewController，则首次viewWillAppear时isBeingPresented为YES，如果是UITabBarController、UINavigationController等的子视图，则首次viewWillAppear时isMovingToParentViewController为YES，反之为NO。我们通过demo来验证，在此我直接贴上结果：

2019-01-15 15:52:52.996965+0800 test[87924:3898152] 
RootViewController, isBeingPresented = NO isMovingToParentViewController = NO
2019-01-15 15:52:53.011739+0800 test[87924:3898152] 
ModalVC: isBeingPresented = YES isMovingToParentViewController = NO
2019-01-15 15:52:53.017630+0800 test[87924:3898152] 
 TestVC: isBeingPresented = NO isMovingToParentViewController = YES
// 去到下级页面再返回
2019-01-15 15:52:55.875078+0800 test[87924:3898152] 
 TestVC: isBeingPresented = NO isMovingToParentViewController = NO

在对应VC的viewWillAppear方法进行打印，TestVC是导航栈上的vc，可以看到结果和官方注释一致。同时发现window的rootViewController的isBeingPresented和isMovingToParentViewController 都是 NO。isBeingDismissed和isMovingFromParentViewController同理。

最后感谢大家的阅读，欢迎指出问题和提出建议。